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Chen, Song [Verfasser]. "Large scale structures and radio galaxy survey / Song Chen." Bielefeld : Universitätsbibliothek Bielefeld, 2015. http://d-nb.info/1078112479/34.
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MacDonald, Emily Christine. "Large scale structure in the Oxford-Dartmouth thirty degree survey." Thesis, University of Oxford, 2004. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.409816.
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Ratcliffe, Andrew. "Large scale structure in the Durham/UKST Galaxy Redshift Survey." Thesis, Durham University, 1996. http://etheses.dur.ac.uk/5345/.
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The initial results from the Durham/UKST Galaxy Redshift Survey are presented here. Using this redshift survey the luminosity, clustering and dynamical properties of galaxies in the Universe are investigated. The 3-D distribution of galaxies in the Durham/UKST survey appears "cellular” on 50-100h(^-1) Mpc scales (where h is Hubble's constant in units of 100 kms(^-1) Mpc(^-1)) and is clearly more complex than a simple 1-D periodic pattern. The optical galaxy luminosity function of the Durham/UKST survey is estimated and can be fit by a Schechter function. Comparison with other determinations of the luminosity function shows good agreement, favouring a flat faint end slope to M(_b J) ~ -14.The redshift space 2-point correlation function clustering statistic is estimated from the Durham/UKST survey. Comparison with previous estimates from other redshift surveys again shows good agreement and the Durham/UKST survey gives a detection of large scale power above and beyond that of the standard cold dark matter cosmological model on 10-40h(^-1)Mpc scales. The projected correlation function is also estimated from the Durham/UKST survey and is compared with models for the real space 2-point correlation function. To estimate this real space correlation function directly, a new application of the Richardson-Lucy inversion technique is developed, tested and then applied to the Durham/UKST survey. The effects of redshift space distortions on the 2-point correlation function are investigated and modelled in the non-linear and linear regimes. The 1-D pairwise velocity dispersion of galaxies is measured to be 416 ± 36 kms(^-1) which, while being consistent with the canonical value of ~ 350 kms(^-1) is slightly smaller than recently measured values. However, this value is inconsistent with the ~ 1000 kms(^-1) value as measured in the standard cold dark matter cosmological model at a high level of significance. The ratio of the mean mass density of the Universe, Ω, and the linear bias factor, b (relating the galaxy and light distributions), is then calculated to be Ω(^0.6)/b = 0.45 ± 0.38. This favours either an open (Ω < 1) and unbiased (b = 1) Universe or a flat (Ω = 1) and biased (b ~ 2) Universe.
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Rezaie, Mehdi. "Robust Measurements of the Large-Scale Clustering of Galaxy Survey Data." Ohio University / OhioLINK, 2009. http://rave.ohiolink.edu/etdc/view?acc_num=ohiou1626320867298365.
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Rezaie, Mehdi. "Robust Measurements of the Large-Scale Clustering of Galaxy Survey Data." Ohio University / OhioLINK, 2021. http://rave.ohiolink.edu/etdc/view?acc_num=ohiou1626320867298365.
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Lautenschläger, Thea, Mawunu Monizi, Macuntima Pedro, Mandombe José Lau, Makaya Futuro Bránquima, Christin Heinze, and Christoph Neinhuis. "First large-scale ethnobotanical survey in the province of Uíge, northern Angola." BioMed Central, 2018. https://tud.qucosa.de/id/qucosa%3A31820.
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Background: Angola suffered a long-lasting military conflict. Therefore, traditional knowledge of plant usage is still an important part of cultural heritage, especially concerning the still very poor health care system in the country. Our study documents for the first time traditional knowledge of plant use of local Bakongo communities in the northern province of Uíge on a large scale with a focus on medicinal plants and puts data in context to different parameters of age, gender and distance to the provincial capital.
Methods: Field work was carried out during nine field trips in 13 municipalities between October 2013 and October 2016. In 62 groups, 162 informants were interviewed. Herbarium specimens were taken for later identification. Database was analysed using Relative Frequency of Citations, Cultural Importance Index, and Informant Consensus Factor. Furthermore, significances of influence of age, gender and distance were calculated.
Results: Our study presents 2390 use-reports, listing 358 species in 96 plant families, while just three out of 358 mentioned species are endemic to Angola about one-fifth are neophytes. The larger the distance, the higher the number of use citations of medical plants. Although women represent just a fifth of all citations (22%), their contribution to medicinal plants was proportionally even higher (83%) than those of men (74%). Fifty percent of all plants mentioned in the study were just listed by men, 12% just by women. We made some new discoveries, for example. Gardenia ternifolia seems to be promising for treatment of measles, and Annona stenophylla subsp. cuneata has never been ethnobotanically nor phytochemically investigated.
Conclusions: While the study area is large, no significant influence of the distance in regard to species composition in traditional healer’s concepts of the respective village was pointed out. Although several plants were just mentioned by women or men, respectively, no significant restriction to gender-specific illnesses in medical plant use could be found. Merely concerning the age of informants, a slight shift could be detected.
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Marinello, Batalla Gabriel Esteban Eugenio. "Re-assessment of the large scale structure in the 2dF galaxy redshift survey." Tesis, Universidad de Chile, 2011. http://repositorio.uchile.cl/handle/2250/102565.
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Magíster en Ciencias, Mención AstronomíaLa distribución de galaxias a gran escala define una compleja red de filamentos, murallas y vacíos de galaxias, situándose los cúmulos de galaxias en la intersección de filamentos. A dicha red se la conoce como “Estructura a Gran Escala” (LSS por su sigla en inglés), cuya forma general y relación entre sus componentes provee información sobre la distribución general de materia, que depende del modelo cosmológico, y la formación de las galaxias, siendo necesario perfeccionar continuamente su caracterización en la medida que hay avances significativos en las bases de datos o en los métodos de análisis. Nuestro trabajo esta basado en el reciente catálogo VOCLUDET de cúmulos y grupos de galaxias, construido en forma automatizada a partir del catálogo de corrimientos al rojo de galaxias llamado “2-degree Galaxy Redshift Survey” (2dFGRS) mediante el metodo geometrico de Voronoi, el cual consta de dos secciones, una norte, del North Galactic Pole (NGP), y una sur, del South Galactic Pole (SGP). La utilización de cúmulos de galaxias en el trazado de la LSS tiene las ventajas, frente al uso directo de las galaxias, por no estar ellos afectados por el efecto distorsionador llamado “Dedos de Dios” (Fingers-of-God) y porque se pueden estimar individualmente sus masas totales. A partir de un análisis exhaustivo del catálogo VOCLUDET, se definio una muestra de 745 cúmulos caracterizados por altos valores de su dispersión de velocidad (HVDCS por su sigla en inglés), > 400 km/s, correspondientes por lo tanto preferentemente a cúmulos masivos. Nuestro análisis indica que las propiedades de los cumulos de esta muestra no presentan un efecto de selección importante con la distancia, hasta aquella correspondiente a z~0.15, por lo que en este trabajo hemos limitado el mapeo de la LSS hasta z~0.15. Incluimos el catalogo de la muestra HVDCS en este trabajo, que consiste en el listado de los siguientes parametros calculados: ascensión recta, declinación, redshift, distancia comóvil, Ngal, v , masa virial, radio promedio. Para obtener el trazado de la estructura a gran escala hemos calculado, en 3 dimensiones, el Árbol Recubridor Mínimo (Minimal Spanning Tree, MST), el cual es un trazador cuantitativo y objetivo de la LSS, revelando la estructura filamentaria de las cadenas a las cuales pertenecen los cúmulos de la muestra HVDCS. El análisis de las propiedades del MST de la distribución de estos cúmulos indica que la topología global de su distribución espacial es consistente con una distribución con una geometría filamentaria a escalas mayores que la distancia promedio entre cúmulos y de una geometría tipo plano a escalas más pequeñas. Usando el mismo MST, realizamos una búsqueda sistemática de supercúmulos en el 2dFGRS. Nuestro catálogo de supercúmulos en el 2dFGRS consiste en 55 y 73 detecciones de supercúmulos en las secciones NGP y SGP, respectivamente. Se estimó la significancia estadística de cada supercúmulo y se extrajo una muestra de supercúmulos de alta significancia en su detección, consistente de 35 y 49 supercúmulos en el NGP y SGP, respectivamente. Hemos encontrado que la mayoría de los supercúmulos identificados tienen algún grado de correspondencia con aquellos de catálogos de supercúmulos previos en el volumen del 2dFGRS. Del estudio de la geometría y población de nuestros supercúmulos encontramos que los supercúmulos pobres, constituidos por menos de 10 cúmulos de galaxias, son muy numerosos y filamentarios, formado por simples cadena de cúmulos, mientras que los superćumulos ricos son muy escasos, con un gran número de cúmulos y poseyendo en su interior cadenas de cúmulos “tipo araña”. Incluimos el catalogo de los supercúmulos encontrados en este trabajo, que consiste en el listado de los siguientes parámetros calculados: ascensión recta, declinación, redshift, distancia comóvil, Ncl, p-value del test de significancia, cúmulos miembros, filamentariedad del grafo, largos de los ejes principales y volumen del elipsoide envolvente, y los descriptores de forma y la triaxialidad.
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Ward, Alexander P. "Modelling Response Patterns for A Large-Scale Mail Survey Study Using Mixture Cure Models." The Ohio State University, 2019. http://rave.ohiolink.edu/etdc/view?acc_num=osu1555587554123989.
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Manzoor, Numan, and Umar Shahzad. "Information Visualization for Agile Development in Large‐Scale Organizations." Thesis, Blekinge Tekniska Högskola, Sektionen för datavetenskap och kommunikation, 2012. http://urn.kb.se/resolve?urn=urn:nbn:se:bth-3094.
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Context: Agile/lean development has been successful situations where small teams collaborate over long periods of time with project stakeholders. Unclear is how such teams plan and coordinate their work in such situations where inter-dependencies with other projects exist. In large organizations, scattered teams and complex team structure makes it difficult for every stakeholder to have a clear understanding of project information. These factors make it difficult for large‐scale organizations to adopt the agile/lean development paradigm. Objectives: The goal of conducting this study is to find the information visualization techniques that ease or resolve the challenges of agile development in large-scale organizations. The study reports the challenges of agile development and information visualization techniques in literature and reported by industrial experts. Additionally, proposed a guideline that how information visualization technique can be used to ease or resolve related challenge of agile development. Methods: For this particular study, two research methodologies are used; Systematic Literature Review (SLR) and Industrial Survey. Two SLRs are performed for finding 1) challenges of agile development and 2) information visualization techniques in agile development. Data sources like Engineering Village (Inspec/ Compendex), IEEE Explore digital library, ACM digital library, Science Direct, ISI-Web of knowledge; Scopus were used to select primary study. Industrial survey was conducted in order to obtain empirical evidence to our findings. In survey, mainly questions were related to challenges of agile development and information visualization techniques practiced by industrial experts. Results: 84 different challenges of agile development found in literature and by applying grounded theory we found 9 distinct categories of challenges. There were 55 challenges reported by industrial experts in survey which later grouped into 10 distinct challenges. 45 information visualization techniques found in literature and grouped into 21 distinct technologies. There were 47 different information visualization techniques reported by industrial experts. When we grouped these techniques there were 9 distinct technologies found by applying open, axial and selective coding of grounded theory Conclusions: Systematic Literature Review and Industrial Survey confirmed that information visualization techniques can be used to ease or resolve challenges of agile development. Along with other visualization techniques, Data Flow Diagrams, UML, Use Case Diagrams, Burn Down Charts, Scrum Story Board, Kanban Boards and Gantt Chart are highly reported techniques found through systematic literature review and later confirmed by industrial experts. On the other hand, through survey we found that industrial experts mainly rely on informal and customized information visualization techniques to visualize information.
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Sánchez, C., J. Clampitt, A. Kovacs, B. Jain, J. García-Bellido, S. Nadathur, D. Gruen, et al. "Cosmic voids and void lensing in the Dark Energy Survey Science Verification data." OXFORD UNIV PRESS, 2017. http://hdl.handle.net/10150/623046.
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Cosmic voids are usually identified in spectroscopic galaxy surveys, where 3D information about the large-scale structure of the Universe is available. Although an increasing amount of photometric data is being produced, its potential for void studies is limited since photometric redshifts induce line-of-sight position errors of >= 50 Mpc h(-1)which can render many voids undetectable. We present a new void finder designed for photometric surveys, validate it using simulations, and apply it to the high-quality photo-z redMaGiC galaxy sample of the DES Science Verification data. The algorithm works by projecting galaxies into 2D slices and finding voids in the smoothed 2D galaxy density field of the slice. Fixing the line-of-sight size of the slices to be at least twice the photo-z scatter, the number of voids found in simulated spectroscopic and photometric galaxy catalogues is within 20 per cent for all transverse void sizes, and indistinguishable for the largest voids (R-v >= 70 Mpc h(-1)). The positions, radii, and projected galaxy profiles of photometric voids also accurately match the spectroscopic void sample. Applying the algorithm to the DES-SV data in the redshift range 0.2 < z < 0.8, we identify 87 voids with comoving radii spanning the range 18-120 Mpc h(-1), and carry out a stacked weak lensing measurement. With a significance of 4.4 sigma, the lensing measurement confirms that the voids are truly underdense in the matter field and hence not a product of Poisson noise, tracer density effects or systematics in the data. It also demonstrates, for the first time in real data, the viability of void lensing studies in photometric surveys.
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Ding, Zhejie. "Systematics Study and Detection of Baryon Acoustic Oscillations from Future Galaxy Survey and Weak Lensing Survey." Ohio University / OhioLINK, 2019. http://rave.ohiolink.edu/etdc/view?acc_num=ohiou1554330484538948.
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Kwan, J., C. Sánchez, J. Clampitt, J. Blazek, M. Crocce, B. Jain, J. Zuntz, et al. "Cosmology from large-scale galaxy clustering and galaxy–galaxy lensing with Dark Energy Survey Science Verification data." OXFORD UNIV PRESS, 2017. http://hdl.handle.net/10150/623270.
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We present cosmological constraints from the Dark Energy Survey (DES) using a combined analysis of angular clustering of red galaxies and their cross-correlation with weak gravitational lensing of background galaxies. We use a 139 deg(2) contiguous patch of DES data from the Science Verification (SV) period of observations. Using large-scale measurements, we constrain the matter density of the Universe as Omega(m) = 0.31 +/- 0.09 and the clustering amplitude of the matter power spectrum as sigma(8) = 0.74 +/- 0.13 after marginalizing over seven nuisance parameters and three additional cosmological parameters. This translates into S-8 = sigma(8)(Omega(m)/0.3)(0.16) = 0.74 +/- 0.12 for our fiducial lens redshift bin at 0.35 < z < 0.5, while S-8 = 0.78 +/- 0.09 using two bins over the range 0.2 < z < 0.5. We study the robustness of the results under changes in the data vectors, modelling and systematics treatment, including photometric redshift and shear calibration uncertainties, and find consistency in the derived cosmological parameters. We show that our results are consistent with previous cosmological analyses from DES and other data sets and conclude with a joint analysis of DES angular clustering and galaxy-galaxy lensing with Planck Cosmic Microwave Background data, baryon accoustic oscillations and Supernova Type Ia measurements.
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Wang, Jianqiang. "Estimating the distance distribution of subpopulations and testing observation outlyingness for a large-scale complex survey." [Ames, Iowa : Iowa State University], 2008.
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Alpaslan, Mehmet. "The cosmic web unravelled : a study of filamentary structure in the Galaxy and Mass Assembly survey." Thesis, University of St Andrews, 2014. http://hdl.handle.net/10023/4906.
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I have investigated the properties of the large scale structure of the nearby Universe using data from the Galaxy and Mass Assembly survey (GAMA). I generated complementary halo mass estimates for all groups in the GAMA Galaxy Group Catalogue (G³C) using a modified caustic mass estimation algorithm. On average, the caustic mass estimates agree with dynamical mass estimates within a factor of 2 in 90% of groups. A volume limited sample of these groups and galaxies are used to generate the large scale structure catalogue. An adapted minimal spanning tree algorithm is used to identify and classify structures, detecting 643 filaments that measure up to 200 Mpc/h, each containing 8 groups on average. A secondary population of smaller coherent structures, dubbed `tendrils,' that link filaments together or penetrate into voids are also detected. On average, tendrils measure around 10 Mpc/h and contain 6 galaxies. The so-called line correlation function is used to prove that tendrils are real structures rather than accidental alignments. A population of isolated void galaxies are also identified. The properties of filaments and tendrils in observed and mock GAMA galaxy catalogues agree well. I go on to show that voids from other surveys that overlap with GAMA regions contain a large number of galaxies, primarily belonging to tendrils. This implies that void sizes are strongly dependent on the number density and sensitivity limits of the galaxies observed by a survey. Finally, I examine the properties of galaxies in different environments, finding that galaxies in filaments tend to be early-type, bright, spheroidal, and red whilst those in voids are typically the opposite: blue, late-type, and more faint. I show that group mass does not correlate with the brightness and morphologies of galaxies and that the primary driver of galaxy evolution is stellar mass.
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Ahmadi, Parisa. "Analysis of traffic patterns for large scale outdoor events : A case study of Vasaloppet ski event." Thesis, KTH, Trafik och logistik, 2012. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-96506.
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Vasaloppet is a cross country ski event which has been held in Sweden for about 50 years. Now more than 50,000 people of different ages participate in various cross country ski races during the Vasaloppet winter week in Dalarna County. This increasing demand needs good traffic and transportation planning to avoid congestion and provide safe, on time and environmentally friendly transportation for participants and visitors to the area. The key for a good event traffic planning is reliable and up-to-date traffic data which is not available for the Vasaloppet winter week. This study is an attempt to collect traffic data in order to find the movement patterns in the area and estimate origin-destination matrices for the main event of Vasaloppet week. Based on resources and time limitation it was decided to use a web-base d participants’ survey in order to collect traffic data. The link to the survey was sent to email address of a sample of 5000 participants. About 64% of the participants drove from their home town to the area and about 31 percent travelled by bus. Train and airplane have a very small share in travel mode to the area. Malungsälen, Mora and Älvdalen are three municipalities in Dalarna County with the highest share in accommodating participants. On the day of the race, bus and car have approximately the same share in travel mode with 45% and 47% respectively.
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Saro, A., S. Bocquet, J. Mohr, E. Rozo, B. A. Benson, S. Dodelson, E. S. Rykoff, et al. "Optical-SZE scaling relations for DES optically selected clusters within the SPT-SZ Survey." OXFORD UNIV PRESS, 2017. http://hdl.handle.net/10150/624426.
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We study the Sunyaev-Zel'dovich effect (SZE) signature in South Pole Telescope (SPT) data for an ensemble of 719 optically identified galaxy clusters selected from 124.6 deg(2) of the Dark Energy Survey (DES) science verification data, detecting a clear stacked SZE signal down to richness lambda similar to 20. The SZE signature is measured using matched-filtered maps of the 2500 deg(2) SPT-SZ survey at the positions of the DES clusters, and the degeneracy between SZE observable and matched-filter size is broken by adopting as priors SZE and optical mass-observable relations that are either calibrated using SPT-selected clusters or through the Arnaud et al. (A10) X-ray analysis. We measure the SPT signal-to-noise zeta - lambda relation and two integrated Compton-y Y500-lambda relations for the DES-selected clusters and compare these to model expectations that account for the SZE-optical centre offset distribution. For clusters with lambda > 80, the two SPT-calibrated scaling relations are consistent with the measurements, while for the A10-calibrated relation the measured SZE signal is smaller by a factor of 0.61 +/- 0.12 compared to the prediction. For clusters at 20 < lambda < 80, the measured SZE signal is smaller by a factor of similar to 0.20-0.80 (between 2.3 sigma and 10 sigma significance) compared to the prediction, with the SPT-calibrated scaling relations and larger lambda clusters showing generally better agreement. We quantify the required corrections to achieve consistency, showing that there is a richness-dependent bias that can be explained by some combination of (1) contamination of the observables and (2) biases in the estimated halo masses. We also discuss particular physical effects associated with these biases, such as contamination of. from line-of-sight projections or of the SZE observables from point sources, larger offsets in the SZE-optical centring or larger intrinsic scatter in the lambda-mass relation at lower richnesses.
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Sánchez, Alonso Carles. "Dark energy properties from the combination of large-scale structure and weak gravitational lensing in the dark energy survey." Doctoral thesis, Universitat Autònoma de Barcelona, 2017. http://hdl.handle.net/10803/457878.
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Aquesta tesi doctoral es centra en l’extracció d’informació cosmològica utilitzant cartografiats de galàxies fotomètrics, en particular el Dark Energy Survey (DES), tot minimitzant l’impacte dels efectes sistemàtics predominants. La tesi inclou treball tant en les fases inicials com finals de l’anàlisi de dades de DES, des del càlcul de desplaçaments cap al vermell (redshifts) fotomètrics i tests als possibles efectes sistemàtics en la mesura de formes de galàxies, a l’estimació de paràmetres cosmològics utilitzant la combinació d’informació d’estructura a gran escala i lents gravitacionals febles.
A la tesi es presenta la primera demostració de la fiabilitat dels redshifts fotomètrics obtinguts amb la càmera de DES, utilitzant un conjunt nombrós d’algoritmes i dades del període de validació de la ciència de DES (Science Verification, SV) conjuntament amb dades de cartografiats espectroscòpics com ara VVDS, zCOSMOS i ACES. En aquesta part presentem una àmplia comparació de mètodes de càlcul de redshifts fotomètrics utilitzant dades reals de DES.
Respecte a lents gravitacionals febles, a la tesi es caracteritza la senyal al voltant de galàxies per una varietat de mostres, incloent testatge exhaustiu d’efectes sistemàtics i l'estudi del biaix de galàxies, el qual descriu com les galàxies poblen halos de matèria fosca. A part de l'ús de galàxies com a lents, també s’estudia la senyal de lent gravitacional produïda per buits còsmics, per primer cop en un cartografiat fotomètric, utilitzant un nou algoritme per trobar buits que s’ha dissenyat en aquesta tesi concretament per tals conjunts de dades, i que s’ha aplicat aplicar també a l'estudi de l’efecte anomenat Sachs-Wolfe.
Com a peça central de la tesi, es presenten les mesures de correlacions angulars de galàxies i de lents gravitacionals febles al voltant de galàxies vermelles lluminoses en el conjunt de dades DES-SV i es combinen per produir el primer anàlisi cosmològic de la combinació d’estructura a gran escala i lents gravitacionals a DES. Els resultats no són competitius amb els del satèl·lit Planck (DES-SV comprèn només aproximadament 3% de la mostra de dades final de DES) però és consistent amb anàlisis independents amb les mateixes dades i estableix un marc en el modelat i tractament d'errors sistemàtics per combinacions futures de mesures a DES i a la generació pròxima de cartografiats de de galàxies com LSST, WFIRST i Euclid.This PhD thesis is focused on extracting cosmological information from photometric galaxy surveys, in particular the Dark Energy Survey, while minimizing the impact of dominant systematic errors. The thesis includes work on both the first and last stages of survey data analysis, from photometric redshifts (photo-z’s) and shear systematics testing to cosmological parameter estimation using large-scale structure (LSS) and weak gravitational lensing (WL). I performed the first assessment of the photo-z capabilities of the DES Camera by using an extensive set of photo-z algorithms, and data from the DES Science Verification (SV) period matched to spectroscopic data from surveys like VVDS, zCOSMOS and ACES. That part provides a thorough comparison between training and template-based photo-z methods using real data. On WL, I characterized the galaxy-galaxy lensing signal for a variety of galaxy samples, including exhaustive systematics testing and the study of the galaxy bias, which describes the way galaxies populate dark matter halos. Beyond the usage of galaxies as lenses, I also studied the lensing signal produced by cosmic voids, for the first time in a photometric survey, using a new void finder I designed specifically for such data sets, and which has been applied as well to the study of the Integrated Sachs-Wolfe effect. As a major piece of work in the thesis, I measured the angular galaxy clustering and galaxy-galaxy lensing of luminous red galaxies in the DES-SV sample and combined them to conduct the first cosmological analysis from the combination of LSS and WL probes in DES. The results are not competitive with those from Planck (DES-SV comprises only about 3% of the final DES data sample) but show consistency with the DES cosmic shear analysis and establish a benchmark in the modeling and treatment of systematic errors for future combinations of probes in DES and the next generation of galaxy surveys like LSST, WFIRST and Euclid.
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Pensa, Francesco <1981>. "Marine biodiversity survey in the Northern Red Sea: a large-scale monitoring carried out in collaboration with volunteer divers." Doctoral thesis, Alma Mater Studiorum - Università di Bologna, 2013. http://amsdottorato.unibo.it/5832/.
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Concerns over global change and its effect on coral reef survivorship have highlighted the need for long-term datasets and proxy records, to interpret environmental trends and inform policymakers. Citizen science programs have showed to be a valid method for collecting data, reducing financial and time costs for institutions. This study is based on the elaboration of data collected by recreational divers and its main purpose is to evaluate changes in the state of coral reef biodiversity in the Red Sea over a long term period and validate the volunteer-based monitoring method. Volunteers recreational divers completed a questionnaire after each dive, recording the presence of 72 animal taxa and negative reef conditions. Comparisons were made between records from volunteers and independent records from a marine biologist who performed the same dive at the same time. A total of 500 volunteers were tested in 78 validation trials. Relative values of accuracy, reliability and similarity seem to be comparable to those performed by volunteer divers on precise transects in other projects, or in community-based terrestrial monitoring. 9301 recreational divers participated in the monitoring program, completing 23,059 survey questionnaires in a 5-year period. The volunteer-sightings-based index showed significant differences between the geographical areas. The area of Hurghada is distinguished by a medium-low biodiversity index, heavily damaged by a not controlled anthropic exploitation. Coral reefs along the Ras Mohammed National Park at Sharm el Sheikh, conversely showed high biodiversity index. The detected pattern seems to be correlated with the conservation measures adopted. In our experience and that of other research institutes, citizen science can integrate conventional methods and significantly reduce costs and time. Involving recreational divers we were able to build a large data set, covering a wide geographic area. The main limitation remains the difficulty of obtaining an homogeneous spatial sampling distribution.
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Bautista, Julian Ernesto. "Baryon acoustic oscillations in the large scale structures of the universe as seen by the Sloan Digital Sky Survey." Paris 7, 2014. http://www.theses.fr/2014PA077132.
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Ce manuscrit décrit la mesure des oscillations acoustiques des baryons (BAO) en utilisant des forêts Lyman-alpha et des galaxies, et son interprétation cosmologique. Entre 2011 et 2014, le télescope du Sloan Digital Sky Survey III a observé le spectre de plus de 1,3 millions de galaxies et plus de 150 000 quasars lointains dans le cadre du projet Baryon Oscillation Spectroscopic Survey (BOSS), en visant la mesure la plus précise des BAO dans la distribution de matière à grande échelle. Nous décrivons l'analyse des donnés, l'interprétation cosmologique et des tests avec des données simulées. Nous présentons une nouvelle méthode pour générer des données simulées, utilisées pour étudier des effets systématiques qui pourraient affecter la mesure. Aucun de ces effets ne change significativement nos résultats. Avec les données disponibles en 2014, le pic BAO est mesuré avec une précision de 3% dans la direction radiale et 5% dans la direction transverse à = 2,34. Nous comparons nos résultats avec des mesures précédentes, en particulier celles du satellite Planck, et nous trouvons un accord au niveau de 1,8ơThis thesis describes the measurement of the baryon acoustic oscillations using Lyman-alpha forests and galaxies and its cosmological interprétation. From 2011 to 2014, the Sloan Digital Sky Survey III telescope observed spectra of — 1. 3 million galaxies and ∽ 150 000 quasars in the context of the Baryon Oscillation Spectroscopic Survey (BOSS). This project aimed the most accurate BAO measurement in the large scale distribution of matter. We describe the data analysis, the cosmological interprétation and tests using mock data. We present a new method to generate mock data, that was used to study systematic effects potentially affecting our measurement. No evidence for a systematic bias comming from these tests could be found. Using data available in 2014, the BAO peak is measured at 3% precision in the radial direction and 5% in the transverse direction, at z = 2. 34. We compare our results with previous measurements, in particular those from the Planck satellite, and we find an agreement at 1. 8ơ level
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Chabanier, Solène. "Neutrinos and dark matter cosmology with the Lyman-α forest : the interplay between large-scale evolution and small-scale baryonic physics." Thesis, université Paris-Saclay, 2020. http://www.theses.fr/2020UPASP034.
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Bien que le modèle cosmologique standard LCDM offre un cadre remarquablement en accord avec de nombreuses observations indépendantes, beaucoup de mystères persistent. En particulier, la masse des neutrinos est toujours inconnue. De par leur masse non nulle, ils laissent une empreinte sur les grandes structures de l'univers à travers l'échelle à laquelle ils diffusent, qui se manifeste comme un déficit de fluctuations de densité de matière aux petites échelles. Par ailleurs, le modèle de matière noire froide montre des tensions persistantes avec les observations sur des échelles inférieures au Mpc. Dans ce travail de thèse, j'utilise le spectre de puissance de la transmission de flux dans la forêt Lyman-α dans des spectres de quasars lointains afin de contraindre la somme des masses des neutrinos et étudier la plausibilité d'un modèle de matière noire tiède. Dans un premier temps, j'ai mesuré le spectre de puissance 1D de la forêt Lyα à 13 redshifts tel que 2 ≤ z ≤ 4.25 en utilisant 43,751 spectres de quasars de haute qualité des programmes BOSS et eBOSS du relevé spectroscopique SDSS. Afin d'obtenir des résultats robustes sachant que les incertitudes statistiques ont été réduites d'un facteur 3 par rapport à la mesure précédente, j'ai identifié et contrôlé plusieurs effets systématiques dans l'analyse de données. Modéliser le flux Lyα implique de recourir à des simulations hydrodynamiques cosmologiques sachant qu'il émerge de la combinaison complexe entre l'évolution des grandes structures et de la physique baryonique des petites échelles. En effet, les processus astrophysiques tels que la formation stellaire et les phénomènes de retro-action de supernovae et des trous noirs rejettent une quantité considérable d'énergie dans le milieu environnant et modifient l'état thermique et la distribution du gaz dans le milieu intergalactique. Afin d'améliorer les prédictions théoriques de la forêt Lyα à un niveau comparable des données, je contrains l'impact des mécanismes de retro-action des trous noirs sur le spectre de puissance Lyα grâce à un jeu de 8 simulations que j'ai produit en me basant sur des observations astrophysiques et qui couvre l'ensemble des modèles de feedback plausibles. Je fournis une correction analytique de cet effet ainsi qu'une limite supérieure et inférieure tel que 2 ≤ z ≤ 4.25 et je montre qu'ignorer un tel mécanisme induit un biais de 2σ sur n_s et 1σ sur σ_8. Finalement, je combine les mesure des spectres de puissance Lyα avec des données CMB et BAO afin de les comparer statistiquement aux prédictions théoriques des simulations hydrodynamiques pour améliorer la contrainte sur la somme des masses des neutrinos de Σ mν < 0.12 eV établie précédemment à Σ mν < 0.09 eV dans le cas le plus extrême à 95% de vraisemblance. Ce résultat indique une préférence des données pour un modèle normal de hiérarchie de masse. La combinaison des données Lyα eBOSS avec les données Lyα XQ-100, contraint la masse des reliques thermiques à m_X > 5.3 keV à 95% de vraisemblance dans un cas de modèle de matière noire entièrement constitué de matière noire tiède, ce qui se traduit par une limite supérieure sur les neutrinos stériles produits de manière non-résonante à mν_s > 34 kev. Aussi, les données Lyα-eBOSS confirme une tension existante avec les données CMB sur l'indice spectral n_s et indique une préférence pour une dépendance d'échelle non nulle de n_s à 3σEven if the standard cosmological LCDM model provides a remarkably successful framework to explain many independent observations, it still faces many challenges. In particular, the masses of neutrinos are still unknown and significantly alter structure formation because of their free-streaming that suppresses density fluctuations below a typical length scale inversely proportional to their rest mass. In addition, the cold dark matter (CDM) scenario is in tension with observations on scales smaller than the Mpc. In this thesis work, I use the power spectrum of the transmitted flux in the Lyman-α forest of distant quasar spectra to constrain the sum of neutrino masses, Σ mν, and determine the plausibility of a warm dark matter model, which is conveniently consistent with cold dark matter predictions on large scales while circumventing its issues at small scales because of its non-negligible velocity dispersion. First I measure the 1D power spectrum of the Lyα forest of 43,751 high quality quasar spectra between 2 ≤ z ≤ 4.6 from the BOSS and eBOSS programs of the SDSS spectroscopic survey. To obtain robust results given the unprecedented statistical power of the data I perform a careful investigation of observational systematic sources and their sources. Modeling the Lyα flux power spectrum requires to run hydrodynamical cosmological simulations because it arises from the complex interplay between large-scale structure evolution and small-scale baryonic physics. Indeed, astrophysical processes such as star formation or AGN feedback inject energy in the ambient medium and strongly impact the thermal state and gas distribution in the intergalactic medium. Including such processes in hydrodynamical simulations requires to rely on arbitrary parameters calibrated on astrophysical observations leading to discrepancies between different state-of-the-art simulations. In order to improve theoretical predictions of the Lyα forest, I constrain the impact of AGN feedback using a series of 8 hydro-cosmological simulations covering the whole plausible range of feedback models. I provide upper and lower limit for this signature for 2 ≤ z ≤ 4.25 and also show that ignoring this effect leads to 2σ shift on n_s and 1σ shift on σ_8. Finally, I combine the Lyα flux power spectrum measurements with CMB data, BAO data and theoretical predictions from hydrodynamical simulations to enhance the previously established constraints on the sum of neutrino masses from Σ mν < 0.12 eV to the most stringent constraints to date Σ mν < 0.09 eV in the most extreme case with 95% confidence, which tends to favor the normal hierarchy neutrino mass scenario. Combining eBOSS with XQ-100 Lyα data the mass m_X of hypothetical thermal relics is constrained to m_X > 5.3 keV at the 95% confidence level in the case of a pure warm dark matter scenario, which translates into mν_s > 34 kev for non-resonantly produced sterile neutrinos. Also, a mild-tension is found on n_s between eBOSS Lyα and CMB data, which translates into a preference for a non-zero running of n_s at the level of about 3σ
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Murray, Calum. "Galaxy cluster cosmology with the Euclid Dark Energy Survey." Thesis, Université de Paris (2019-....), 2020. http://www.theses.fr/2020UNIP7063.
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La formation des amas de galaxies dépend à la fois de l’histoire de l’expansion de l’univers, de l’effondrement gravitationnel au-delà de la théorie linéaire et de la composition de l’univers. En tant que telles, les observations des amas avec Euclid fourniront des contraintes cosmologiques importantes sur la nature de l’énergie noire. Dans cette thèse, nous présentons le modèle de drifting diffusive barrier de la fonction de masse du halo et sa précision pour le modèle standard de la cosmologie ΛCDM ansi qu’un modèle d’énergie noire dynamique, plus précisément le modèle de Quintessence. Par la suite, nous présentons les contraintes cosmologiques anticipées par le satellite Euclid qui sont les résultats de notre collaboration parisienne. Dans le dernier chapitre, nous présentons des estimations de masse des amas par des effets de lentillage faible pour un échantillon de 488 amas de galaxies du catalogue redMaPPer SDSS DR8. Nous utilisons des données de lentillage faible de Hyper-Suprime Cam. A partir d’un ensemble de propriétés des amas, mesurées à partir des galaxies contenues dans l’amas, nous examinons les corrélations entre ces propriétés et leurs masses estimées par le lentillage faible. Puis nous analysons plus en profondeur leurs profils de densité projetés en superposant les signaux de lentillage faible en fonction de ces propriétés. Nous sommes notamment en mesure d’examiner les profils de densité projetés des amas qui ont des signaux de lentillage plus ou moins élevés en fonction de notre relation richesse-masse estimée. Cela nous permet de discuter des propriétés physiques des amas de galaxies dont les signaux de lentillage sont moins forts que ceux anticipés par leur richesse. Nous voyons qu’à richesse fixée, les signaux de lentillage plus ou moins élevés ont des profils de densité projetés indiscernables á petite distance du centre de l’amas. L’origine de ce phénomène n’est pas claire et mérite des investigations supplémentaires. Notre relation masse-richesse est en désaccord significatif avec les résultats de la calibration du Dark Energy Survey (DES) (McClintock et al., 2019), la compréhension de l’origine de ce désaccord peut aider à résoudre la tension significative entre l’abondance du cluster DES résultats (DES et al., 2020) et toutes les autres sondes cosmologiquesThe formation of galaxy clusters depend sensitively on the expansion history of the universe, gravitational collapse beyond linear theory and the composition of the universe. As such, cluster observations with Euclid will provide important cosmological constraints on the nature of dark energy. In this thesis, we present the drifting diffusive barrier model of the halo mass function and its accuracy for the standard model of cosmology ΛCDM and a dynamical dark energy model, specifically Quintessence. Subsequently we present the cosmological constraints anticipated by the forthcoming Euclid satellite as the results of our Paris collaboration. In the concluding chapter we present weak lensing mass estimates for a sample of 488 galaxy clusters from the redMaPPer SDSS DR8 catalogue using HSC weak lensing data. We develop an iterative matched filter method and use this method to estimate weak lensing masses for each of the galaxy clusters in our sample. We look at the correlations between a set of cluster properties measured from thecluster member galaxies an d their estimated weak lensing masses, and then analyse in greater their projected density profiles by stacking the lensing signals based upon these properties. Notably, we are able to look at the projected density profiles of clusters which have low or high lensing signals according to our estimated mass-richness relation allow- ing us to discuss the physical properties of low lensing signal galaxy clusters. We see that at fixed richness the low and high lensing signals have indistinguishable pro- jected density profiles at low radii, the origin of which is unclear and merits further investigation. Our calibrated mass-richness relation is in significant disagreement with the results of the Dark Energy Survey (DES) calibration (McClintock et al., 2019), understanding the origin of this disagreement may help to resolve the significant tension between the DES cluster abundance results (DES et al., 2020) and all other cosmological probes
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Broadhead, Dawn. "Large scale entrance surface dose survey and organ dose measurements during diagnostic radiology using the Harshaw 5500 and 6600 TLD systems." Thesis, University of Newcastle Upon Tyne, 2001. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.366517.
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Xiao, Ying. "Mining crop sequence patterns at a large regional scale : A case from mainland France." Thesis, Université de Lorraine, 2015. http://www.theses.fr/2015LORR0122/document.
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L’objectif principal de cette thèse est d’instruire l’organisation des successions culturales, à l’échelle de la France et sur un recul décennal, tant en terme de cinétiques localisées qu’en terme de dynamiques liées à des variables explicatives du milieu physique et socio-technico-économiques. Ce travail de « fouille de données » est appliqué en France métropolitaine, en utilisant les bases de données publiques disponibles. Notre étude couvre la période 1992-2003 où s’implémenta la réforme de 1992 de la Politique Agricole Commune européenne et l’agenda 2000 en France. A partir d’une fouille de données sur l’ensemble des points Terruti sur cette période, 2549 successions culturales de trois ans furent identifiées. Ensuite, 21 clusters de l’ensemble des 430 régions agricoles (RA) françaises, quatre systèmes de culture, 90 RA, parangons des 430 RA, et trois régions principales appartenant à cinq des 21 clusters, regroupant les cultures de céréales, oléagineux et protéagineux, ont été définis. Deux approches de cinétiques des successions ont été réalisées : Une étude envisageant les successions de culture qui suivent les retournements de prairies permanentes. Une recherche des dynamiques d’évolution de successions culturales en lien avec des conditions externes. Nous proposons une utilisation ultérieure des méthodes mobilisées qui ont montré leur capacité à cartographier les grandes tendances d’évolution en France et à identifier les principales variables explicatives de ces évolutions. Les apports de cette thèse contribuent à améliorer notre compréhension des processus qui organisent les successions culturales en France et construisent par ces pratiques agricoles très dynamiques des impacts forts sur le territoire agricole françaisIn the context of changing agricultural policy, the development of agricultural production systems, increasing concern for agricultural sustainability and shifts in agricultural land management practice-related land-use change, the main objective of this thesis was to mine crop sequence patterns (CSP) and the relationships between CSP and the biophysical and socio-technical-economic conditions in mainland France from historical census data (e.g. land-cover survey, agricultural censuses, population census). Our study period 1992-2003 covers the implementation period of the 1992 European Union Common Agricultural Policy reform and Agenda 2000 in France. Both the classical statistical and data mining technique were applied in alone or combined ways in this thesis. First, we proposed an innovative approach to representing CSP within a given area and period at a large regional scale in a stationary way. The 2549 3-year crop sequences (CSs) were first identified as major CSs within all 430 agricultural districts (ADs) in mainland France during this period. Next, 21 clusters of ADs , four types of cropping systems, 90 representative ADs and three principal planting zones of cereals, oilseeds, and protein crops belonging to five clusters identified previously were further defined. We then explored CSP in a dynamic way by investigating CSP after grassland-to-cropland conversion, the temporal variability of CSP, and the evolution of the relationships between CSP and the external conditions over the study period. We conclude that the approaches developed here permit the representation of CSP at the large regional scale in both stationary and dynamic ways using time series land-cover data denoting specific agricultural cover types. The findings of this thesis contribute to improving the understanding of the process and pattern of human land management practices by agriculture affecting the terrestrial biosphere
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Porredon, Diez de Tejada Anna Maria. "Multi-probe cosmological analysis with the dark energy survey." Doctoral thesis, Universitat Autònoma de Barcelona, 2019. http://hdl.handle.net/10803/669428.
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Les actuals i futures cartografies de galàxies cobriran un major volum i recolliran imatges de millor qualitat que les obtingudes fins ara, permetent mesures precises de la última etapa de l'Univers i proves potents de la naturalesa de l’energia fosca i la Relativitat General.
Aquests cartografiats ens permetran obtenir informació cosmològica a partir de diversos observables, i la combinació d'aquests pot millorar la robustesa i precisió dels resultats de l'anàlisi.
Aquesta tesi es centra en la combinació de diferents traçadors de l'estructura a gran escala (LSS) per tal d'obtenir mesures dels paràmetres cosmològics més precises. Primer, combinem la distribució de galàxies de la mostra corresponent al primer any de dades del Dark Energy Survey (DES Y1) amb la distorsió de la radiació còsmica de fons (CMB) deguda a la matèria fosca on viuen aquestes galàxies (CMB lensing) provinent de la combinació òptima entre el South Pole Telescope i Planck. En aquest anàlisi obtenim mesures en el biaix galàctic, la funció de creixement de LSS i paràmetres cosmològics. Els nostres resultats són consistents amb el model estàndard (\LCDM) i altres resultats de DES Y1. La informació que podem obtenir de l'anàlisi està limitada per les restriccions d'escala, però esperem que millori en els futurs anàlisis.
A continuació, combinem la distribució de galàxies de dues mostres diferents (en l'anomenat mètode multi-traçador) per analitzar els senyals de distorsió en la distribució de galàxies deguda a les seves velocitats ``peculiars'' (RSD) i de la possible contribució no-Gaussiana a les fluctuacions inicials de la distribució de matèria (PNG). Per a aquest propòsit, considerem un parell de mostres optimistes (amb gran nombre de galàxies i diferències en el biaix) i les mostres de DES del 3r any d'observacions (DES Y3) que actuaran con a lents gravitatòries. Trobem que les mesures en RSD poden millorar un factor cinc a distàncies properes i les mesures en PNG un factor tres o més. També comprovem l'impacte d'incloure CMB lensing en l'anàlisi, en el qual no variem la cosmologia, trobant que majoritàriament millora les mesures en el biaix.
Per últim, definim i optimitzem una de galàxies limitada en magnitud que s'utilitzarà per les mesures de la distribució de galàxies en l'anàlisi de DES Y3, actuant com a lent gravitacional respecte a galàxies més llunyanes (lens sample). Per aquest propòsit, ens basem en previsions de Fisher i posem a prova com aquestes canvien al variar el nombre de galàxies i la incertesa en la posició donat un conjunt de talls en magnitud. També caracteritzem l'impacte en els nostres resultats de diferents particions de la mostra en intervals de desplaçament al vermell (redshift), tant per aquesta mostra com per l'altra lens sample (REDMAGIC).
Finalment, les nostres previsions mostren que amb aquesta mostra que hem optimitzat podem obtenir mesures un 15\% més precises que amb REDMAGIC.Ongoing and future photometric surveys will enable detailed measurements of the late-time Universe and powerful tests of the nature of dark energy and General Relativity. These surveys will be able to obtain cosmological constraints from multiple probes, and the combination of these probes can improve their robustness and constraining power. This thesis is focused on the combination of multiple tracers of large-scale structure (LSS) to obtain tighter cosmological constraints. First, we combine the galaxy clustering from the Dark Energy Survey (DES) Year 1 (Y1) data with CMB lensing from the optimal combination of South Pole Telescope (SPT) and Planck, obtaining constraints on the galaxy bias, the growth function and the cosmological parameters. Our results are consistent with \LCDM$ $ and other measurements of DES Y1. However, their constraining power is limited due to conservative scale cuts. We expect an improved signal-to-noise in future analyses. We then combine the galaxy clustering of two different galaxy samples (the so-called multi-tracer approach) to explore the constraints on redshift space distortions (RSD) and primordial non-Gaussianities (PNG). For this purpose, we consider a pair of optimistic samples (with large bias differences and number densities) and the DES Year 3 (Y3) lens samples. We find that the constraints on RSD can be improved a factor of five at low redshift with respect to a single tracer, and the constraints on PNG can be improved more than a factor three. We also test the impact of including CMB lensing cross-correlations in our analysis, in which we keep the cosmology fixed, finding it mainly improves the galaxy bias constraints. Last, we define and optimize a magnitude limited galaxy sample to be used for the galaxy clustering measurements in the DES Y3 analysis, in combination with galaxy-galaxy lensing. We rely on Fisher forecasts, and we test how these change given the variations obtained for the number density and estimated redshift uncertainty for a set of magnitude cuts. We also characterize the impact of redshift binning choices in our cosmological constraints for this sample and the other DES Y3 lens sample: REDMAGIC. Finally, our forecasts show that we can potentially obtain 15\% tighter constraints with this magnitude limited sample, compared to REDMAGIC.
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Gadoni, Lorenzo. "Analysis of the relationships between Spartina maritima and nutrient enrichment in North Adriatic salt marshes." Master's thesis, Alma Mater Studiorum - Università di Bologna, 2015. http://amslaurea.unibo.it/8436/.
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Salt marshes are coastal ecosystem in the upper intertidal zone between internal water and sea and are widely spread throughout Italy, from Friuli Venezia Giulia, in the North, to Sicily, in the South. These delicate environments are threatened by eutrophication, habitat conversion (for land reclaiming or agriculture) and climate change impacts such as sea level rise.
The objectives of my thesis were to: 1) analyse the distribution and biomass of the perennial native cordgrass Spartina maritima (one of the most relevant foundation species in the low intertidal saltmarsh vegetation in the study region) at 7 sites along the Northern Adriatic coast and relate it to critical environmental parameters and 2) to carry out a nutrient manipulation experiment to detect nutrient enrichment effects on S. maritima biomass and vegetation characteristics.
The survey showed significant differences among sites in biological response variables - i.e., live belowground, live aboveground biomass, above:belowground (R:S) biomass ratio, % cover, average height and stem density – which were mainly related to differences in nitrate, nitrite and phosphate contents in surface water. Preliminary results from the experiment (which is still ongoing) showed so far no significant effects of nutrient enrichment on live aboveground and belowground biomass, R:S ratio, leaf %Carbon, average height, stem density and random shoot height; however, a significantly higher (P=0.018) increase in leaf %Nitrogen content in treated plots indicated that nutrient uptake had occurred.
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López-Osorio, Sara [Verfasser]. "Eimeriosis in ruminants: large-scale epidemiological survey, isolation of a new Eimeria zuernii strain and novel data on Eimeria spp.-host cell interactions / Sara López-Osorio." Gießen : Universitätsbibliothek, 2020. http://d-nb.info/1219981869/34.
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Prince, Michael William. "Strategic planning in construction firms : perceptions and personal characteristics of the manager, strategic planning behaviour, and subjective performance in a large scale survey of the Canadian construction industry." Thesis, University of Bradford, 1988. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.385648.
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Vielzeuf, Pauline Eva. "Cross-correlations in the dark energy survey: from redshift distribution inference to probes of gravity with the cosmic microwave background." Doctoral thesis, Universitat Autònoma de Barcelona, 2018. http://hdl.handle.net/10803/665098.
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During the past decades, we have been the witnesses of unprecedented advancements in the
understanding of our universe dynamics and evolution. Indeed, together with the theory General
Relativity (GR) by Albert Einstein at the beginning of the 1900’s, the improvement of observational
tools have led to the establishment of the standard model of cosmology the so-called
∧-cold-Dark-Matter model (∧CDM) that is so far the simplest model that describes best our
universe considering observations. However, this standard model suffers from caveats, more
specifically the presence in the theory of two dark components, Dark Energy and Dark Matter.
Understanding the mystery behind these two components have become the leading objective of
observational cosmology today, and of current experiments, as it is the case of the Dark Energy
Survey (DES), that will after 5 years of observations image about 300 million galaxies with an
unprecedented depth covering one eighth of the sky (5000 sq. deg.).
This thesis is based on the analysis of the first year of observation of DES (DESY1) and more in
particular on the use of cross-correlation techniques in cosmological analyses. Here, we expose
two of different possible use of cross-correlation. Namely, we first show how cross-correlation
techniques has been employed as a tool to infer redshift distribution of objects using the socalled
clustering-redshift methodologies. And moreover how for the first time this techniques
have entered in the cosmological analyses to correct the mean of the redshift distributions of the
DESY1 galaxy catalog with shapes (the weak lensing sample) inferred by typical photometric
techniques. We explain how using simulation we have evaluated systematics errors induced by
our overall methodology and present the full methodology employed for redshift distribution
determination of the DESY1 Weak lensing sample.
In a second time, we expose how we have been using cross-correlations as a probe of ∧CDM
cosmology using in one hand cross-correlation between cosmic voids identified in the DESY1
catalogs and the lensing map from the Planck satellite and on the other hand simulated ∧CDM
cosmology. More specifically, recent results have suggested an excess signal in the observed
void catalogs imprint in the Cosmic Microwave Background temperature maps with respect to
simulated ∧CDM cosmology, we reiterate the procedure using this time the lensing maps of
the CMB. After optimizing our void catalogs in simulation, looking for population of voids
responsible for the more significant detection,we could detect the imprint of DESY1 cosmic
voids with a significance of ~ 7 – 12ơ with a discrepancy of ~ 3 – 9ơ with respect to ∧CDM
simulations.
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Wang, Lingyu. "Large-scale structures from infrared surveys." Thesis, Imperial College London, 2008. http://hdl.handle.net/10044/1/4410.
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To use the AKARI All-Sky Survey Point Source Catalogue as a validation sample for future missions such as Planck and to study large-scale structure, we first investigate the AKARI point source detection limit at 90 μm and the nature of bright spurious sources. Due to the degradation of the sensitivity of the AKARI All-Sky Survey and formidable difficulties in filtering out excessive noise, we return to the IRAS Faint Source Catalog to construct a redshift catalogue of over 60,000 galaxies selected at 60 μm, the Imperial IRAS-FSC Redshift Catalogue (IIFSCz). Around 50% of the sources in the IIFSCz have spectroscopic redshifts and a further 20% have photometric redshifts. The luminosity and selection functions are obtained for the IIFSCz flux-limited at 0.36 Jy at 60 μm. The dependence of galaxy clustering on spectral type and luminosity is studied using correlation statistics. A possible detection of the baryon acoustic oscillations in the power spectrum of the flux-limited sample of the IIFSCz is discussed. Finally, we present future research directions which include the FIR-radio correlation, ultraluminous and hyperluminous infrared galaxies, galaxy bias in the SWIRE Photometric Redshift Catalogue and convergence of the cosmological dipole.
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Zubík, Tomáš. "Vyhotovení mapových podkladů areálu Metra v Blansku - jižní část." Master's thesis, Vysoké učení technické v Brně. Fakulta stavební, 2019. http://www.nusl.cz/ntk/nusl-400183.
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The diploma thesis deals with planimetric and altimetry determination of the area Metro company in Blansko , its southern part. The content of the thesis is a detailed description of the schedule, survey section, calculations, graphic processing in the GEOSTORE V6® program, description information connection. The result is a printed 1: 250 scale maps in the S-JTSK coordinate system and the Bpv elevation system.
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Blake, Christopher. "Large-scale structure via wide-area radio surveys." Thesis, University of Oxford, 2002. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.249329.
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Goddard, Daniel Stephen. "Mapping galaxy properties with large-scale galaxy surveys." Thesis, University of Portsmouth, 2018. https://researchportal.port.ac.uk/portal/en/theses/mapping-galaxy-properties-with-largescale-galaxy-surveys(43eec926-30d1-44bc-8270-86222d389bff).html.
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Large scale observations of the Universe have highlighted that a galaxy’s mass, morphology, and environment are all key factors in a galaxy’s evolution. To what extent each of these contribute however, is still an openly debated question. In this thesis, I attempt to address the aforementioned question providing original research based on a sample of galaxies gathered from the MaNGA IFU survey. Stellar population properties are derived from the data using a newly developed full spectral fitting code, FIREFLY, and state of the art stellar population models. A number of tests using mock galaxies, globular clusters and data from the SDSS DR7 are conducted with FIREFLY in an attempt to assess the codes ability to accurately recover stellar population properties and star formation histories. FIREFLY recovers galaxy properties reliably down to S/N ≥ 5 and S/N ≥ 10 for mock galaxies with both simple and complex star formation histories, respectively. The ages and metallicities derived for globular clusters and galaxies from the SDSS are in good agreement with determinations from colour-magnitude diagram fitting, stellar spectroscopy and other full spectral fitting codes. FIREFLY is then applied to MaNGA data enabling three scientific analyses to be conducted. First, I construct a value added catalogue based on the spatially resolved stellar population properties of MaNGA galaxies, derived from both FIREFLY and absorption line-strength indices. Secondly, I investigate the dependence of light- and mass-weighted stellar population properties, and their radial gradients, on galaxy mass and morphology. Full star formation and metal enrichment histories are reconstructed, and the impact of different stellar population models and full spectral fitting routines on the derived properties is quantified. Light-weighted age gradients are found to be flat for early-type galaxies, and negative for late-type galaxies (∼− 0.11 dex/Re), suggesting an ‘inside-out’ formation of discs. Mass weighted age gradients of early-types are positive (∼0.09 dex/Re) pointing to an ‘outside-in’ progression of star formation. Negative metallicity gradients are detected for both morphological types, but these are significantly steeper in late-types. Metallicity gradients correlate with galaxy mass, with negative gradients becoming steeper with increasing mass. The correlation is stronger for late-types, with a slope of d(∇[Z/H])/d(logM)∼−0.2±0.05, compared to d(∇[Z/H])/d(logM)∼− 0.05 ± 0.05 for early-types. Lastly, I study the effect of galaxy environment on the derived stellar population gradients using three complementary measures of environment, namely the Nth nearest neighbour method, the tidal strength parameter, Q, and distinguishing between central and satellite galaxies. In all cases, no significant correlation between the gradients and environment is found, both at fixed galaxy mass, and for both morphologies. The scientific analysis presented in this thesis suggests that the cumulative merger history of galaxies plays a relatively small role in shaping their metallicity gradients and that internal processes, such as supernova and AGN feedback, matter most to the determination of stellar population gradients. These results set stringent constraints on future models of galaxy formation and evolution.
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Etherington, James Daniel Lambert. "Measuring galaxy environment in large scale photometric surveys." Thesis, University of Portsmouth, 2016. https://researchportal.port.ac.uk/portal/en/theses/measuring-galaxy-environment-in-large-scale-photometric-surveys(acd86f3b-67cd-4684-8d88-e49bb54790c6).html.
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The properties of galaxies, such as the galaxy red fraction and galaxy stellar mass function, have been shown to depend upon their environment in the local Universe. Large scale photometric surveys such as the DES and in the future Euclid, will be vital to gain insight into the evolution of galaxy properties and the role of environment through cosmic time. Large samples come at the cost of redshift precision and this affects the measurement of galaxy environment. In this thesis an analysis pipeline is constructed to derive galaxy parameters including absolute magnitudes, stellar masses and galaxy environments. The analysis pipeline consists of well established components, such as HYPERZ, that performs SED fitting and components that I have developed and tested, including codes to compute galaxy environment. Five methods to compute galaxy environment are implemented, including three fixed aperture methods, based on spheres, cylinders and cones, the Nth nearest neighbour method and the adaptive Gaussian method. The codes are optimized and parallelized and are executed on Portsmouth’s high performance computer cluster. The codes are thoroughly tested using mock data. Further testing is conducted employing GAMA data, with an external collaborator. The pipeline is applied to two datasets and the results lead to two scientific papers: Etherington & Thomas (2015) and Etherington et al. (in DES collaboration review). The first study is based on a low redshift sample drawn from the SDSS. Spectroscopic and photometric redshifts and also simulated photometric redshifts with a range of uncertainties are employed to study the impact of photometric redshift uncertainty on measures of environment as a function of the aperture parameters. The photometric environments are found to have a smaller dynamic range compared to the spectroscopic measurements because uncertain redshifts scatter galaxies from dense environments into less dense environments. With the optimal aperture parameter values, even for large redshift uncertainties, ∼ 0.1, there is a Spearman Rank Correlation Coefficient of ∼ 0.4 between the photometric measurements and the spectroscopic benchmark environments. This is sufficient to extract an environment signal from large scale photometric surveys. The second study in this thesis is based on the science verification data from the DES. This is the first set of observations from the survey. This study uses ∼3.2 million galaxies from the SPT-East (South Pole Telescope) field that covers approximately 100 sq. deg. of the sky. From the grizY photometry the analysis pipeline is used to derive galaxy stellar masses and absolute magnitudes. The errors on these properties are assessed using Monte-Carlo simulations sampled from the full photometric redshift probability distributions. Galaxy environments are computed using a fixed conical aperture method, for a range of scales. Galaxy environment probability distribution functions are constructed and the dependence of the environment errors on the aperture parameters is investigated. The environment components of the galaxy stellar mass function for the redshift range: 0.15 < z < 1.05 are calculated. For z < 0.75 it is found that the fraction of massive galaxies is larger in high density environment than low density environments. The low and high density components converge with increasing redshift to z ∼ 1.0 where the shapes of the mass function components are indistinguishable. This redshift is important because it marks the transition between an earlier epoch where the mass distribution of galaxies is independent of environment and a later epoch where the mass distribution does depend on galaxy environment. This study shows the build up of high density structures around massive galaxies, through cosmic time. The results in this thesis demonstrate that large scale photometric surveys can produce competitive galaxy evolution science, enabling further investigations of the role of galaxy environment. This is hugely encouraging for current and future experiments.
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Croom, Scott Martin. "Cosmology and large-scale structure from quasar redshift surveys." Thesis, Durham University, 1997. http://etheses.dur.ac.uk/5033/.
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Our aim in this thesis is to use the clustering of QSOs to investigate large- scale structure and cosmology. We are particularly concerned with estimating the cosmological parameters which govern the evolution of structure in the Universe. We first investigate how QSOs trace the distribution of 'normal' galaxies by measuring the correlation between a sample of ~ 150 QSOs and faint, b(_j) < 23 galaxies. At z < 1.5 we find that the cross-correlation amplitude is marginally negative. This low signal clearly rules out models in which QSOs inhabit rich environments. The environments of QSOs are more similar to those of average galaxies. The slight negative correlation can be explained by gravitational lensing, but this has no effect on our conclusions concerning QSO environments. We determine the clustering properties of a combined sample of > 1500 QSOs including the LBQS and Durham/AAT QSO surveys. This data set has a clustering amplitude Ɛ(10 h(^-1) Mpc) = 0.83 ± 0.29 for Ωₒ = 1 at z = 1.27. On ~ 100 – 1000 h(^-1) Mpc scales the limit on detected signals in Ɛ is ±0.025. A model of clustering evolution which includes the effect of bias was used to compare QSO clustering to the clustering of low redshift galaxies and Seyfert galaxies. If Seyferts and QSOs are similarly clustered, then the data prefer a low Ωₒ or high bias for QSOs and galaxies. In contrast, comparisons to the CMB measurements of COBE assuming a CDM-type power spectrum suggest low bias. This might be taken as evidence for low do, but the data is still consistent with Ωₒ = 1 and b(_gp) ~ b(gp) ~ 2..We consider the possibility that nearby galaxy clusters can gravitationally lense background QSOs. We apply the lensing hypothesis to the result of Boyle et al., (1988) and find that cluster masses required are too large. A small dust component could retrieve the lensing model and allow more reasonable mass estimates for clusters from this method. The requirement for a new, deep, wide-field, QSO survey is clear. We discuss the construction of the candidate catalogue for the 2dF QSO Redshift Survey, which will contain ~ 25000 QSOs. We calibrate the photographic plates used for the candidate catalogue and assess the sources of errors and incompleteness. From preliminary spectroscopic observations we conclude that the completeness of the 2dF catalogue is ~ 71.1 ± 7.1%, compared with an estimated completeness of ~ 80%. We propose to substantially increase the catalogue completeness (to ~ 90%), by the introduction of UKST r plates into our candidate catalogue.
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Smith, Alexander Mark Joseph. "Mock catalogues for large scale structure surveys and DESI." Thesis, Durham University, 2018. http://etheses.dur.ac.uk/12866/.
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The upcoming Dark Energy Spectroscopic Instrument (DESI) and Euclid galaxy surveys aim to make the most precise galaxy clustering measurements yet in order to probe the nature of the mysterious dark energy that is thought to make up the majority of the energy density of the Universe today. To reach the required precision, it is essential that the systematics that affect these measurements are understood, which requires realistic mock galaxy catalogues. This thesis focuses on building a mock catalogue for the DESI Bright Galaxy Survey (BGS), and applications of this mock. We outline the methods used to create halo merger trees from N-body and Monte Carlo simulations, which is the first step towards creating a mock catalogue. We show how these methods can be extended beyond ΛCDM to warm dark matter, and show applications. We have developed a halo occupation distribution (HOD) method for creating a BGS mock catalogue from the Millennium-XXL (MXXL) simulation, with galaxies being assigned r-band magnitudes and g-r colours. The mock catalogue is able to reproduce the luminosity function and clustering of the Sloan Digital Sky Survey (SDSS) and Galaxy And Mass Assembly (GAMA) survey at different redshifts. The mock is used to quantify incompleteness in the DESI BGS due to fibre assignment, which depends on the surface density of galaxies, and to assess correlation function correction methods. An inverse pair weighting method is able to provide an unbiased correction on all scales. Finally, we show how the HOD methodology can be extended to construct mock catalogues for Euclid, and other large galaxy surveys.
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Laurent, Pierre. "L'univers aux grandes échelles : études de l'homogénéité cosmique et de l'énergie noire à partir des relevés de quasars BOSS et eBOSS." Thesis, Université Paris-Saclay (ComUE), 2016. http://www.theses.fr/2016SACLS227/document.
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Ce travail de thèse se sépare en deux volets. Le premier volet concerne l'étude de l'homogénéité de l'univers, et le second une mesure de l'échelle BAO, qui constitue une règle standard permettant de mesurer l'évolution du taux d'expansion de l'univers. Ces deux analyses reposent sur l'étude de la structuration (ou clustering) des quasars des relevés BOSS et eBOSS, qui couvrent la gamme en redshift 0,9 < z < 2,8. Les mesures des observables caractérisant la structuration de l'univers aux grandes échelles sont très sensibles aux effets systématiques, nous avons donc étudiés ces effets en profondeur. Nous avons mis en évidence que les sélections de cibles quasars BOSS et eBOSS ne sont pas parfaitement homogènes, et corrigé cet effet. Au final, la mesure de la fonction de corrélation des quasars nous a permis de mesurer le biais des quasars sur la gamme en redshift 0,9 < z < 2,8. Nous obtenons la mesure actuelle la plus précise du biais, b = 3,85 ± 0,11 dans la gamme 2,2 < z < 2,8 pour le relevé BOSS, et b = 2,44 ± 0,04 dans la gamme 0,9 < z < 2,2 pour le relevé eBOSS. Le Principe Cosmologique stipule que notre univers est isotrope et homogène à grande échelle. Il s'agit d'un des postulats de base de la cosmologie moderne. En étudiant la structuration à très grande échelle des quasars, nous avons prouvé l'isotropie spatiale de l'univers dans la gamme 0,9 < z < 2,8, indépendamment de toute hypothèse et cosmologie fiducielle. L'isotropie spatiale stipule que l'univers est isotrope dans chaque couche de redshift. En la combinant au principe de Copernic, qui stipule que nous ne nous situons pas à une position particulière dans l'univers, permet de prouver que notre univers est homogène aux grandes échelles. Nous avons effectué une mesure de la dimension de corrélation fractale de l'univers, D₂(r), en utilisant un nouvel estimateur, inspiré de l'estimateur de Landy-Szalay pour la fonction de corrélation. En corrigeant notre estimateur du biais des quasars, nous avons mesuré (3 - D₂(r)) = (6,0 ± 2,1) x 10⁻⁵ entre 250 h⁻¹ Mpc et 1200 h⁻¹ Mpc pour le relevé eBOSS, dans la gamme 0,9 < z < 2,2. Pour le relevé BOSS, nous obtenons (3 - D₂(r)) = (3,9 ± 2,1) x 10⁻⁵, dans la gamme 2,2 < z < 2,8. De plus, nous montrons que le modèle Lambda-CDM décrit très bien la transition d'un régime structuré vers un régime homogène. D’autre part, nous avons mesuré la position du pic BAO dans les fonctions de corrélation des quasars BOSS et eBOSS, détecté à 2,5 sigma dans les deux relevés. Si nous mesurons le paramètre α, qui correspond au rapport entre la position du pic mesuré et la position prédite par une cosmologie fiducielle (en utilisant les paramètres Planck 2013), nous mesurons α = 1,074 pour le relevé BOSS, et α = 1,009 pour le relevé eBOSS. Ces mesures, combinées uniquement à la mesure locale de H₀, nous permettent de contraindre l'espace des paramètres de modèles au-delà du Lambda-CDMThis work consists in two parts. The first one is a study of cosmic homogeneity, and the second one a measurement of the BAO scale, which provides a standard ruler that allows for a direct measurement of the expansion rate of the universe. These two analyses rely on the study of quasar clustering in the BOSS and eBOSS quasar samples, which cover the redshift range 0.9 < z < 2.8. On large scales, the measurement of statistical observables is very sensitive to systematic effects, so we deeply studied these effects. We found evidences that the target selections of BOSS and eBOSS quasars are not perfectly homogeneous, and we have corrected this effect. The measurement of the quasar correlation function provides the quasar bias in the redshift range 0.9 < z < 2.8. We obtain the most precise measurement of the quasar bias at high redshift, b = 3.85 ± 0.11, in the range 2.2 < z < 2.8 for the BOSS survey, and b = 2.44 ± 0.04 in the range 0.9 < z < 2.2 for the eBOSS survey. The Cosmological Principle states that the universe is homogeneous and isotropic on large scales. It is one of the basic assumptions of modern cosmology. By studying quasar clustering on large scales, we have proved ''spatial isotropy'', i.e. the fact that the universe is isotropic in each redshift bins. This has been done in the range 0.9 < z < 2.8 without any assumption or fiducial cosmology. If we combine spatial isotropy with the Copernican Principle, which states that we do not occupy a peculiar place in the universe, it is proved that the universe is homogeneous on large scales. We provide a measurement of the fractal correlation dimension of the universe, D₂(r), which is 3 for an homogeneous distribution, and we used a new estimator inspired from the Landy-Szalay estimator for the correlation function. If we correct our measurement for quasar bias, we obtain (3 - D₂(r)) = (6.0 ± 2.1) x 10⁻⁵ between 250 h⁻¹ Mpc and 1200 h⁻¹ Mpc for eBOSS, in the range 0.9 < z < 2.2. For BOSS, we obtain (3 - D₂(r)) = (3.9 ± 2.1) x 10⁻⁵, in the range 2.2 < z < 2.8. Moreover, we have shown that the Lambda-CDM model provide a very nice description of the transition from structures to homogeneity. We have also measured the position of the BAO peak in the BOSS and eBOSS quasar correlation functions, which yield a 2,5 sigma detection in both surveys. If we measure the α parameter, which corresponds to the ratio of the measured position of the peak to the predicted position in a fiducial cosmology (here Planck 2013), we measure α = 1.074 for BOSS, and α = 1.009 for eBOSS. These measurements, combined only with the local measurement of H₀, allows for constraints in parameter space for models beyond Lambda-CDM
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Bel, Julien. "Les moments cumulant d'ordre supérieur à deux points des champs cosmologiques : propriétés théoriques et applications." Thesis, Aix-Marseille, 2012. http://www.theses.fr/2012AIXM4715/document.
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La philosophie de cette thèse est de dire que nos plus grandes chances de trouver et de caractériser les ingrédients essentiels du modèle cosmologique passe par l'élargissement de l'éventail des méthodes que l'on peut utiliser dans le but de trouver une nouvelle physique. Bien qu'il soit d'une importance primordiale de continuer à affiner, à de-biaiser et à rendre plus puissantes, les stratégies qui ont contribué à établir le modèle de concordance, il est également crucial de remettre en question, avec de nouvelles méthodes, tous les secteurs de l'actuel paradigme cosmologique. Cette thèse, par conséquent, s'engage dans le défi de développer des sondes cosmologiques nouvelle et performantes qui visent à optimiser les résultats scientifiques des futures grand sondages de galaxies. L'objectif est double. Du côté théorique, je cherche à mettre au point de nouvelles stratégies de test qui sont peu (voire pas du tout) affectées par des incertitudes astrophysiques ou par des modèles phénoménologiques qui ne sont pas complet . Cela rendra les interprétations cosmologiques plus facile et plus sûr. Du côté des observations, l'objectif est d'évaluer les performances des stratégies proposées en utilisant les données actuelles, dans le but de démontrer leur potentiel pour les futures grandes missions cosmologiques tels que BigBoss et EUCLIDThe philosophy of this thesis is that our best chances of finding and characterizing the essential ingredients of a well grounded cosmological model is by enlarging the arsenal of methods with which we can hunt for new physics. While it is of paramount importance to continue to refine, de-bias and power, the very same testing strategies that contributed to establish the concordance model, it is also crucial to challenge, with new methods, all the sectors of the current cosmological paradigm. This thesis, therefore, engages in the challenge of developing new and performant cosmic probes that aim at optimizing the scientific output of future large redshift surveys. The goal is twofold. From the theoretical side, I aim at developing new testing strategies that are minimally (if not at all) affected by astrophysical uncertainties or by not fully motivated phenomenological models. This will make cosmological interpretations easier and safer. From the observational side, the goal is to gauge the performances of the proposed strategies using current, state of the art, redshift data, and to demonstrate their potential for the future large cosmological missions such as BigBOSS and EUCLID
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Kolodzig, Alexander. "Large-scale structure studies using AGN in X-ray surveys." Diss., Ludwig-Maximilians-Universität München, 2015. http://nbn-resolving.de/urn:nbn:de:bvb:19-182285.
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Large X-ray surveys are a powerful tool to study the large-scale structure (LSS) of the Universe. The scientific impact of LSS studies using active galactic nuclei (AGN)
in X-ray surveys can be significantly increased by conducting wider and deeper X-ray surveys and studying the surface brightness fluctuations of the unresolved cosmic X-ray background (CXB).
In the first part of this Thesis, we have investigated the prospects of using the AGN sample to be detected by the upcoming eROSITA all-sky survey (eRASS) for LSS studies. We show that eRASS will detect about 3 million AGN in the 0.5-2.0 keV band. This will result in a ~30 times larger number of sources and a ~30 times better sensitivity than its 25 year old predecessor, the ROSAT all-sky survey (RASS). We show that this unprecedented AGN sample will have a median luminosity of ~10^44 erg/s, which is typical for the entire AGN population in this energy band. It will have a median redshift of z ~ 1 and approximately 40% of the objects will be in the redshift range of z = 1-2, where the bulk of the X-ray emission of AGN is produced. About 10^4 - 10^5 AGN are predicted to be beyond redshift z = 3 and about 2 000 - 30 000 beyond z = 4, which will potentially include some of the earliest AGN in the Universe. We demonstrate that, given these unique properties, the eRASS-AGN sample will be able to significantly improve our current knowledge of the AGN spatial density as a function of redshift and luminosity over a wide range of cosmic time. Further, we show that it will enable us, for the first time, to perform detailed redshift- and luminosity-resolved studies of the clustering strength of X-ray selected AGN. All these measurements will dramatically improve our understanding of the growth of supermassive black holes over cosmic time and its implications for galaxy evolution. We demonstrate for the first time that, given the breadth and depth of eRASS, it will be possible to use AGN as a cosmological probe via baryon acoustic oscillation (BAO) measurements. We will be able to convincingly detect BAOs in the currently uncharted redshift range of z ~ 1-2, which will improve the constraints on the current cosmological model.
In the second part of this Thesis, we have conducted the most accurate measurement to date of the brightness fluctuations of the unresolved CXB in the 0.5-2.0 keV band for angular scales of < ~17'. For this we used the XBOOTES survey, the currently largest continuous survey of the X-ray telescope Chandra. We find that on small angular scales (< ~2') the observed power spectrum of the brightness fluctuations is broadly consistent with the conventional AGN clustering model, although with a 30% deviation. This deviation nevertheless presents a good opportunity to improve our understanding of clustering properties of unresolved AGN by testing more sophisticated clustering models with our measurement. For angular scales of > ~2' we measure a significant excess with up to an order of magnitude difference in comparison to the standard AGN clustering model. We demonstrate that an instrumental origin can be excluded. However, we also show that the excess can neither be explained with any known X-ray source population by looking at strength of its clustering signal and the shape of its energy spectrum. It might be caused by more than one type of source but the dominant source appears to have extragalactic origin. Finally, we make predictions on how eRASS will be able to advance the studies of the unresolved CXB.
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Baruah, Leon. "A galaxy cluster finding algorithm for large-scale photometric surveys." Thesis, University of Sussex, 2015. http://sro.sussex.ac.uk/id/eprint/52966/.
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As the largest gravitationally bound objects in the Universe, galaxy clusters can be used to probe a variety of topics in astrophysics and cosmology. This thesis describes the development of an algorithm to find galaxy clusters using non-parameteric methods applied to catalogs of galaxies generated from multi-colour CCD observations. It is motivated by the emergence of increasingly large, photometric galaxy surveys and the measurement of key cosmological parameters through the evolution of the cluster mass function. The algorithm presented herein is a reconstruction of the successful, spectroscopic cluster finding algorithm, C4 (Miller et al., 2005), and adapting it to large photometric surveys with the goal of applying it to data from the Dark Energy Survey (DES). AperC4 uses statistical techniques to identify collections of galaxies that are unusually clustered in a multi-dimensional space. To characterize the new algorithm, it is tested with simulations produced by the DES Collaboration and I evaluate its application to photometric datasets. In doing so, I show how AperC4 functions as a cosmology independent cluster finder and formulate metrics for a \successful" cluster finder. Finally, I produce a galaxy catalog appropriate for statistical analysis. C4 is applied to the SDSS galaxy catalog and the resulting cluster catalog is presented with some initial analyses.
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Pizarro, Oscar. "Large scale structure from motion for autonomous underwater vehicle surveys." Thesis, Massachusetts Institute of Technology, 2004. http://hdl.handle.net/1721.1/39185.
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Thesis (Ph. D.)--Joint Program in Applied Ocean Science and Engineering (Massachusetts Institute of Technology, Dept. of Ocean Engineering; and the Woods Hole Oceanographic Institution), 2004.Includes bibliographical references (p. 177-190).
Our ability to image extended underwater scenes is severely limited by attenuation and backscatter. Generating a composite view from multiple overlapping images is usually the most practical and flexible way around this limitation. In this thesis we look at the general constraints associated with imaging from underwater vehicles for scientific applications - low overlap, non-uniform lighting and unstructured motion - and present a methodology for dealing with these constraints toward a solution of the problem of large area 3D reconstruction. Our approach assumes navigation data is available to constrain the structure from motion problem. We take a hierarchical approach where the temporal image sequence is broken into subsequences that are processed into 3D reconstructions independently. These submaps are then registered to infer their overall layout in a global frame. From this point a bundle adjustment refines camera and structure estimates. We demonstrate the utility of our techniques using real data obtained during a SeaBED AUV coral reef survey. Test tank results with ground truth are also presented to validate the methodology.
by Oscar Pizarro.
Ph.D.
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Van, De Rijt Nicolas. "Signatures of the primordial universe in large-scale structure surveys." Palaiseau, Ecole polytechnique, 2012. http://pastel.archives-ouvertes.fr/docs/00/72/78/11/PDF/PhDthesis.pdf.
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L'étude des grandes structures de l'Univers est un des meilleurs moyens pour comprendre l'origine et l'évolution de l'Univers. Dans cette thèse, nous nous spécialisons aussi bien dans la théorie des perturbations aux échelles cosmologiques, que dans le cisaillement cosmique. La théorie des perturbations aux échelles cosmologiques décrit comment les grandes structures de l'Univers se sont formées à partir des minuscules fluctuations primordiales. Cette évolution est généralement décrite en se servant des équations du mouvement d'un fluide, et dans cette thèse nous introduisons quelques nouvelles versions de cette hiérarchie de Boltzmann. Les avantages et inconvénients de ces nouvelles hiérarchies sont analysés en détail. Nous introduisons aussi une nouvelle technique, appelée l'approximation eikonal, qui nous permet de mieux comprendre les résultats des autres approches utilisées en théorie des perturbations. En outre, grâce à sa généralité, elle nous permet de généraliser une grande quantité de résultats. Le cisaillement cosmique décrit comment l'effet des lentilles gravitationnelles déforme notre image du ciel. Dans cette thèse, nous étudions de manière détaillée le bispectre du cisaillement cosmique, au deuxième ordre en les potentiels gravitationnels. Le calcul est intégralement fait en "full sky", généralisant ainsi les résultats existants. Pour simplifier les calculs numériques, nous introduisons et généralisons l'approximation dite de LimberThe study of the large-scale structure of the Universe is one of the most important tools used to understand the origin and evolution of the Universe. In this thesis, we focus on two different facets of this study: cosmological perturbation theory and cosmic shear. Cosmological perturbation theory describes how the large-scale structure of the Universe has been created out of the tiny initial perturbations. This evolution is described using fluid equations, and in this thesis, we introduce new versions of this Boltzmann hierarchy. The advantages and disadvantages of each hierarchy are thoroughly analysed. We also introduce a novel technique, dubbed the eikonal approximation, which enables us to better understand the results of existing perturbation theory approaches. Moreover, its broad range of applicability allows us to generalise many results. Cosmic shear describes how gravitational lensing deforms the image of the sky. In this thesis, we compute in great detail the bispectrum of cosmic shear to second order in the gravitational potentials. The complete calculation is done on the full sky, making the results much more general than the existing ones. To ease the otherwise impossible numerical calculations, we introduce the (extended) Limber approximation
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Ntelis, Pierros. "Probing Cosmology with the homogeneity scale of the universe through large scale structure surveys." Thesis, Sorbonne Paris Cité, 2017. http://www.theses.fr/2017USPCC200/document.
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Cette thèse présente ma contribution à la mesure de l’échelle d’homogénéité à l’aide de galaxies, avec l’interprétation cosmologique des résultats. En physique, tout modèle est constitué par un ensemble de principes. La plupart des modèles de cosmologie sont basés sur le principe cosmologique, qui indique que l’univers est statistiquement homogène et isotrope à grande échelle. Aujourd’hui, ce principe est considéré comme vrai car il est respecté par ces modèles cosmologiques qui décrivent avec précision les observations. Cependant, l’isotropie de l’univers est maintenant confirmée par de nombreuses expériences, mais ce n’est pas le cas pour l’homogénéité. Pour étudier l’homogénéité cosmique, nous proposons un postulat d’homogénéité cosmique. Depuis 1998, les mesures des distances cosmiques à l’aide de supernovae de type Ia, nous savons que l’univers est maintenant en phase d’expansion accélérée. Ce phénomène s’explique par l’ajout d’une composante énergétique inconnue, appelée énergie sombre. Puisque l’énergie noire est responsable de l’expansion de l’univers, nous pouvons étudier ce fluide mystérieux en mesurant le taux d’expansion de l’univers. L’échelle d’oscillation acoustique Baryon (BAO). En mesurant cette échelle à différents moments de la vie de notre univers, il est alors possible de mesurer le taux d'expansion de l’univers et donc de caractériser cette énergie sombre. Alternativement, nous pouvons utiliser l’échelle d’homogénéité pour étudier cette énergie sombre. L’étude l’échelle de l’homogénéité et l’échelle BAO réclament l’étude statistique du regroupement de la matière de l’univers à grandes échelles, supérieure à plusieurs dizaines de Megaparsecs. Les galaxies et les quasars sont formés dans les vastes surdensités de la matière et ils sont très lumineuses: ces sources tracent la distribution de la matière. En mesurant les spectres d’émission de ces sources en utilisant de larges études spectroscopiques, telles que BOSS et eBOSS, nous pouvons mesurer leurs positions. Il est possible de reconstruire la distribution de la matière en trois dimensions en volumes gigantesques. Nous pouvons ensuite extraire divers observables statistiques pour mesurer l’échelle BAO et l’échelle d’homogénéité de l’univers. En utilisant les catalogues de diffusion de données 12 de la version 12 de données, nous avons obtenu une précision sur l’échelle d’homogénéité réduite de 5 par rapport la mesure de WiggleZ. À grande échelle, l’univers est remarquablement bien décrit en ordre linéaire selon le modèle LCDM, le modèle standard de la cosmologie. En général, il n’est pas nécessaire de prendre en compte les effets non linéaires qui compliquent le modèle à petites échelles. D’autre part, à grande échelle, la mesure de nos observables devient très sensible aux effets systématiques. Ceci est particulièrement vrai pour l’analyse de l’homogénéité cosmique, qui nécessite une méthode d’observation. Afin d’étudier le principe d’homogénéité d’une manière indépendante du modèle, nous explorons une nouvelle façon d’inférer des distances en utilisant des horloges cosmiques et SuperNovae de type Ia. C'est la théorie la plus couramment utilisée dans le domaine des hypothèses astrophysiquesThis thesis exposes my contribution to the measurement of homogeneity scale using galaxies, with the cosmological interpretation of results. In physics, any model is characterized by a set of principles. Most models in cosmology are based on the Cosmological Principle, which states that the universe is statistically homogeneous and isotropic on a large scales. Today, this principle is considered to be true since it is respected by those cosmological models that accurately describe the observations. However, while the isotropy of the universe is now confirmed by many experiments, it is not the case for the homogeneity. To study cosmic homogeneity, we propose to not only test a model but to test directly one of the postulates of modern cosmology. Since 1998 the measurements of cosmic distances using type Ia supernovae, we know that the universe is now in a phase of accelerated expansion. This phenomenon can be explained by the addition of an unknown energy component,which is called dark energy. Since dark energy is responsible for the expansion of the universe, we can study this mysterious fluid by measuring the rate of expansion of the universe. Nature does things well: the universe has imprinted in its matter distribution a standard ruler, the Baryon Acoustic Oscillation (BAO) scale. By measuring this scale at different times in the life of our universe, it is then possible to measure the rate of expansion of the universe and thus characterize this dark energy. Alternatively, we can use the homogeneity scale to study this dark energy. Studying the homogeneity and the BAO scale requires the statistical study of the matter distribution of the universe at large scales, superior to tens of Megaparsecs. Galaxies and quasars are formed in the vast overdensities of matter and they are very luminous: these sources trace the distribution of matter. By measuring the emission spectra of these sources using large spectroscopic surveys, such as BOSS and eBOSS, we can measure their positions. It is thus possible to reconstruct the distribution of matter in 3 dimensions in gigantic volumes. We can then extract various statistical observables to measure the BAO scale and the scale of homogeneity of the universe. Using Data Release 12 CMASS galaxy catalogs, we obtained precision on the homogeneity scale reduced by 5 times compared to WiggleZ measurement. At large scales, the universe is remarkably well described in linear order by the ΛCDM-model, the standard model of cosmology. In general, it is not necessary to take into account the nonlinear effects which complicate the model at small scales. On the other hand, at large scales, the measurement of our observables becomes very sensitive to the systematic effects. This is particularly true for the analysis of cosmic homogeneity, which requires an observational method so as not to bias the measurement In order to study the homogeneity principle in a model independent way, we explore a new way to infer distances using cosmic clocks and type Ia SuperNovae. This establishes the Cosmological Principle using only a small number of a priori assumption, i.e. the theory of General Relativity and astrophysical assumptions that are independent from Friedmann Universes and in extend the homogeneity assumption
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Zhang, ZengHua. "Discovery and characterisation of ultra-cool dwarfs in large scale surveys." Thesis, University of Hertfordshire, 2013. http://hdl.handle.net/2299/13900.
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Ultracool dwarfs including the lowest mass stars and substellar dwarfs (or brown dwarfs) is a rapidly evolving and very active field. In this thesis I present the discovery and characterization of ultracool dwarfs and their binary systems with solar and subsolar abundances and try to answer a few scientific questions related to these ultracool objects. I use different techniques based on photometric and astrometric data of modern large scale surveys to identify ultracool dwarfs and their binaries. I identify around 1000 ultracool dwarfs from SDSS, 2MASS and UKIDSS surveys, including 82 L dwarfs and 129 L dwarf candidates (Chapter 2 and 4). This work largely increases the known number of ultracool dwarfs and aid the statistic study of these objects. Eighteen ultracool dwarfs in my sample are found to be in wide binary systems by common proper motion (Chapter 4 and 5). Wide binary systems are often used to test formation theories of low mass stars and brown dwarfs, which have different predictions of separations and binary fractions. One of these binary systems is the first L dwarf companion to a giant star eta Cancri. The eta Cancri B is clearly a useful benchmark object, with constrained distance, age, and metallicity. Further more, the L3.5 dwarf companion eta Cancri B is found to be a potential L4 + T4 binary. I focus on the studies of low mass stars and brown dwarfs with subsolar abundance referred as red and ultracool subdwarfs. They belong to the older Population II of the Galactic halo contain more information of the formation, early evolution and structure of the Milky Way. Using the most extensive optical survey, the Sloan Digital Sky Survey (SDSS), to select low mass stars with subsolar abundance, referred as red subdwarfs with spectral types of late K and M. I identify about 1800 M subdwarfs including 30 new >M6 subdwarfs and five M ultra subdwarfs with very high gravity as well as 14 carbon enhanced red subdwarfs. I also identify 45 red subdwarf binary systems from my red subdwarf sample. Thirty of them are in wide binary systems identified by common proper motion. Fifteen binaries are partially resolved in SDSS and UKIDSS. I estimate the M subdwarf binary fraction. I fit the relationships of spectral types and absolute magnitudes of optical and near infrared bands for M and L subdwarfs. I also measure $UVW$ space velocities of the my M subdwarf sample (Chapter 5). Our studies of the lowest mass stars and brown dwarfs of the Galactic halo are limited by the lack of known objects. There are only seven L subdwarfs published in the literature. I search for ultracool subdwarfs by a combine use of the most extensive optical and near infrared surveys, the SDSS and the UKIRT Infrared Deep Sky Survey. I identify three new L subdwarfs with spectral types of sdL3, sdL7 and esdL6. I re-examine the spectral types and metal classes of all known L subdwarfs and propose to use 2.3 um CO line as an indicator of L subdwarfs. Two of my new L subdwarfs are found to be candidates of halo brown dwarfs (or substellar subdwarfs). I find four of these known ten L subdwarfs could be halo brown dwarfs. I propose a new name "purple dwarf" for lowest-mass stars and brown dwarfs with subsolar abundance (Chapter 3). Finally I summarize and discuss the thesis project in Chapter 6 and describe future research plans in Chapter 7.
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Machado, murtinheiras martins Andre. "Statistical analysis of large scale surveys for constraining the Galaxy evolution." Thesis, Besançon, 2014. http://www.theses.fr/2014BESA2026/document.
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La formation et l'évolution du disque épais de la Voie Lactée restent controversées. Nous avons utilisé un modèle de synthèse de la population de la Galaxie, le Modèle de la Galaxie de Besançon (Robin et al., 2003), qui peut être utilisé pour l'interprétation des données, étudier la structure galactique et tester différents scénarios de formation et évolution Galactique. Nous avons examiné ces questions en étudiant la forme et la distribution de métallicité du disque mince et du disque épais en utilisant l'approche de synthèse de la population. Nous avons imposé sur des simulations les erreurs d'observation et les biais afin de les rendre directement comparables aux observations. Nous avons corrigé les magnitudes et les couleurs des étoiles de la simulation, en utilisant un modèle d'extinction. Les modèles d'extinction disponibles ne reproduisent pas toujours la quantité exacte d'extinction le long de la ligne de visée. Un programme a été développé pour corriger la distribution de l'extinction en fonction de la distance le long de ces lignes. Les extinctions correctes ont ensuite été appliquées sur les simulations du modèle. Nous avons étudié la forme du disque mince en utilisant des données photométriques aux basses latitudes du sondage SDSS-SEGUE. Nous avons comparé qualitativement et quantitativement les observations et les simulations et nous avons essayé de contraindre la fonction de masse initiale. En utilisant la spectroscopie du relevé SEGUE, nous avons sélectionné les étoiles du turn-off de la séquence principale (MSTO) (Cheng et al 2012) et des géantes K pour étudier la distribution de métallicité du disque mince et du disque épais. Nous avons calculé une estimation de distance pour chaque étoile à partir de la relation entre les températures effectives et magnitudes absolues pour les catalogues observés et simulés. Ces deux catalogues ont les mêmes biais sur les distances, elles sont donc comparables. Nous avons développé un outil basé sur une méthode MCMC-ABC pour déterminer la distribution de la métallicité et étudier les corrélations entre les paramètres ajustés. Nous avons confirmé la présence d'un gradient de métallicité radiale de -0.079 ± 0.015 dex kpc−1 pour le disque mince. Nous avons obtenu une métallicité du disque épais au voisinage solaire de -0.47 ± 0.03 dex, compatible avec les résultats obtenus par les études précédentes. De plus, le disque épais ne montre pas de gradient, mais les données sont compatibles avec un gradient positif intérieur suivi d'un négatif extérieur. Nous avons ensuite appliqué les outils développés au relevé spectroscopique Gaia-ESO et calculé la distribution de métallicité des étoiles F/G/K dans le disque mince et épais en supposant une formation en deux époques du disque épais de la Voie Lactée. Nous avons obtenu une métallicité locale dans le disque épais de -0.23 ± 0.04 dex légèrement plus élevée que celle obtenue avec SEGUE mais en accord avec Adibekyan et al. (2013) et un gradient de métallicité radiale du disque épais en accord avec notre analyse précédente des données de SEGUE et la littérature. La métallicité locale est en accord avec la littérature au niveau de 3σ mais parce que les données GES sont préliminaires, une analyse plus approfondie avec plus de données et de meilleurs calibrations doit être faite. L'existence d'un gradient plat dans le disque épais peut être une conséquence d'une formation à partir d’un gaz turbulent et bien homogène, ou bien un fort mélange radial a brassé après coup les étoilesThe formation and evolution of the thick disc of the Milky Way remain controversial. We made use of a population synthesis model of the Galaxy, the Besançon Galaxy Model (Robin et al. 2003), which can be used for data interpretation, study the Galactic structure and test different scenarios of Galaxy formation and evolution. We examined these questions by studying the shape and the metallicity distribution of the thin and thick disc using the population synthesis approach. We imposed on simulations observational errors and biases to make them directly comparable to observations. We corrected magnitudes and colors of stars, from the simulation, using an extinction model. The available extinction models do not always reproduce the exact quantity of extinction along the line of sight. A code to correct the distribution of extinction in distance along these lines have been developed and the corrected extinctions have been applied on model simulations. We studied the shape of the thin disc using photometric data at low latitudes from the SDSS-SEGUE survey. We compared qualitatively and quantitatively observations and simulations and try to constrain the Initial Mass Function. Using the spectroscopic survey SEGUE we selected Main Sequence Turnoff (MSTO) stars (Cheng et al 2012) and K giants to study the metallicity distribution of the thin and thick discs. We computed a distance for each star from the relation between effective temperatures and absolute magnitudes for the observed and simulated catalogs. These two catalogues have the same biases in distances, therefore are comparable. We developed a tool based on a MCMC-ABC method to determine the metallicity distribution and study the correlations between the fitted parameters. We confirmed a radial metallicity gradient of -0.079 ± 0.015 dex kpc−1 for the thin disc. We obtained a solar neighborhood metallicity of the thick disc of -0.47 ± 0.03 dex similar to previous studies and the thick disc shows no gradient but the data are compatible with an inner positive gradient followed by a outer negative one. Furthermore, we have applied the developed tools to the Gaia-ESO spectroscopic survey and computed the metallicity distribution of F/G/K stars in the thin and thick disc assuming a two epoch formation for the thick disc of the Milky Way. We obtained a local metallicity in the thick disc of -0.23 ± 0.04 dex slightly higher than the one obtained with SEGUE but in agreement with Adibekyan et al. (2013) and a radial metallicity gradient for the thick disc in agreement with our previous analysis of SEGUE data and the literature. The local metallicity is in fair agreement with literature at the 3σ level but because the GES data is an internal release under testing further analysis with more data and better calibrations have to be done. The existence of a flat gradient in the thick disc can be a consequence of an early formation from a highly turbulent homogeneous well mixed gas, unless it has suffered heavy radial mixing later on
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Steele, Oliver. "Galaxy spectral analysis in the era of large-scale galaxy surveys." Thesis, University of Portsmouth, 2015. https://researchportal.port.ac.uk/portal/en/theses/galaxy-spectral-analysis-in-the-era-of-largescale-galaxy-surveys(6631e476-60ec-4de3-a536-d8a9e1f8cbc4).html.
Full textAbstract:
In this work I address two of the big questions in modern astrophysics; the role of environment as a driver of galaxy evolution, and the the role of mass in star formation and stellar population evolution. I use one of the most powerful tools available to the astrophysical community, large-scale galaxy spectroscopy, to contribute towards the answers to these dilemmas. I construct a data analysis pipeline based on the public codes gandalf and pPXF to extract gas and stellar dynamics, emission line statistics, absorption line indices and stellar population parameters from these galaxy spectra. I test and calibrate this pipeline against existing results for the Sloan Digital Sky Survey Data Release 7, and find it to provide accurate measurements. I use the emission line results from this to probe the dependence of star formation and ionisation characteristics on stellar mass, local environment and global environment in the Galaxy AND Mass Assembly survey. I find that mass is the main driving factor behind the presence of star formation and determining different ionisation sources, and see a trend with increasing mass from star forming objects to those hosting active galactic nuclei via composites of the two. Local density plays a role only at the highest densities, and is considerably less significant than mass; global environment is found to have negligible impact. This suggests that star formation quenching is primarily a mass-driven process, with active galactic nucleus feedback being a likely candidate for the environment independent process involved in our sample. I stack objects together from the Sloan Digital Sky Survey III: Baryon Oscillation Spectroscopic Survey in order to produce high-signal-to-noise spectra for the purpose of absorption line measurement and the subsequent modelling of stellar population parameters. I use this to investigate the dependence of age, metallicity and α/Fe on mass (using stellar velocity dispersion as a proxy for dynamical mass) and redshift. I find that light-averaged age, metallicity and α/Fe all increase with velocity dispersion, which are predictions of the downsizing paradigm, where the least massive galaxies form their stars later, over more extended timeframes and less effciently than more massive galaxies. Age is also seen to increase with redshift, which is simply the result of everything in the Universe getting older, whilst I see no evidence of metallicity or α/Fe changing with lookback time. Investigating how galaxies age when compared to the Universe, I find that more massive galaxies appear to age faster than the Universe whilst less massive galaxies age slower. I hypothesise that this is due to the different star formation histories of galaxies with differing masses, and test this by compiling models with varying stellar histories and comparing them to our observations. I find that as mass decreases, I require more extended periods of star formation that peak more recently. At the high-mass end, the relationship between the most massive bins is best reproduced by a passively evolving population whose stars formed at higher redshift than I observe. This is a clear result of downsizing, and sets tough restrictions on future models of galaxy formation and evolution.
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Grotefendt, Richard. "Accurate and cost-effective natural resource data from super large scale aerial photography /." Thesis, Connect to this title online; UW restricted, 2005. http://hdl.handle.net/1773/5454.
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Pollina, Giorgia [Verfasser], and Jochen [Akademischer Betreuer] Weller. "Cosmic voids in large-scale structure surveys / Giorgia Pollina ; Betreuer: Jochen Weller." München : Universitätsbibliothek der Ludwig-Maximilians-Universität, 2018. http://d-nb.info/1173616152/34.
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Hatton, Stephen John. "Probing the large-scale structure of the Universe with future galaxy redshift surveys." Thesis, Durham University, 1999. http://etheses.dur.ac.uk/4494/.
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Several projects are currently underway to obtain large galaxy redshift surveys over the course of the next decade. The aim of this thesis is to study how well the resultant three-dimensional maps of the galaxy distribution will be able to constrain the various parameters of the standard Big Bang cosmology. The work is driven by the need to deal with data of far better quality than has previously been available. Systematic biases in the treatment of existing datasets have been dwarfed by random errors due to the small size of the sample, but this will not be the case with the wealth of data that will shortly become available. We employ a set of high-resolution /V-body simulations spanning a range of cosmologies and galaxy biasing schemes. We use the power spectrum of the galaxy density field, measured using the fast Fourier transform process, to develop models and statistics for extracting cosmological information. In particular, we examine the distortion of the power spectrum by galaxy peculiar velocities when measurements are made in redshift space. Mock galaxy catalogues are drawn from these simulations, mimicking the geometries and selection functions of the large surveys we wish to model. Applying the same models to the mock catalogues is not a trivial task, as geometrical effects distort the power spectrum, and measurement errors are determined by the survey volume. We develop methods for assessing these effects and present an in-depth analysis of the likely confidence intervals we will obtain from the surveys on the parameters that determine the power spectrum. Real galaxy catalogues are prone to additional biases that must be assessed and removed. One of these is the effect of extinction by dust in the Milky Way, which imprints its own angular clustering signal on the measured power spectrum. We investigate the strength of this effect for the SDSS survey.
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Galloway, Francis. "Large scale, population-based finite element analysis of cementless tibial tray fixation." Thesis, University of Southampton, 2012. https://eprints.soton.ac.uk/355955/.
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Joint replacements are a common treatment of osteoarthritis, rheumatoid arthritis, or fractures of both the hip and knee. The rising number of procedures being performed each year means that there is a need to assess the performance of an implant design in the general population. The majority of computational studies assessing implants do not take into account inter-patient variability and only use a single patient model. More often than not, it is then assumed that the results can be extrapolated to the general population. This thesis describes a method allowing population-based assessment of joint replacements, focussing on the tibial tray component of a total knee replacement. To generate a large population of models for finite element analysis, two statistical models were used. One was of the tibia, capturing both the variability of the morphology and bone quality, and the other was of the internal knee loads during a gait cycle. Assessment of the statistical models showed that they could adequately generate representative tibiae and gait cycle loads. An automated method was then developed to size, position, and implant the tibial tray in the generated population of tibiae in preparation for finite element analysis. The use of a population-based study, a unique approach compared to current studies, was demonstrated using three case studies assessing the performance of the tibial tray. The first case study examined the factors which might increase the risk of failure of the tibial tray and the effect of under sizing the tibial tray on primary stability. Factors such as bone quality and patient weight were seen to increase the risk of failure. It was found that under sizing the tibial tray did not significantly affect the primary stability of the tibial tray. It was also observed that the peak strain occurred during swing phase of the gait cycle, whereas peak micromotion occurred at the beginning of stance phase of the gait. The second case study investigated the effect of tibia resection depth on primary stability of the tibial tray. A more distal resection was found to increase the peak strain and micromotion of the bone-tray interface. The worsening primary stability with a more distal resection, suggest that to obtain optimal primary stability of the tibial tray it is necessary to resect as little bone as possible. The third case study compared three tibial tray designs. It was ound that the trays with pegs or flanges surrounding the stem tended to perform better, reducing the strain and the micromotion at the bone-tray interface. It was noted that the performance of the trays predicted by the analysis was similar to that observed clinically. This shows the potential use of population-based studies to help predict the clinical outcome of joint replacements.
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Borstad, Eriksen Martin. "Cross-correlating spectroscopic and photometric galaxy surveys." Doctoral thesis, Universitat Autònoma de Barcelona, 2014. http://hdl.handle.net/10803/133261.
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En esta tesis se estudia el acotamiento en los paraámetros cosmología al
combinar observaciones en catálogos de galaxias espectroscópicas y
fotométricos. Los catálogos fotométricos miden las distorsiones de lente
gravitacional débil (WL), mientras que los catalogos espectroscópicos, con más
alta precisión en la información de redshift (o corriento al rojo), son ideales
para el estudio de distorsiones espaciales de redshift (RSD). El análisis
combinado se realiza únicamente com funciones de correlación angular, lo que
simplifica el estudio, en particular en lo que respecta a la inclusión de la
covarianza entre observables.
El primer capítulo presenta un nuevo algoritmo para el cálculo eficaz de las
correlaciones cruzadas de varios marcadores, incluidos WL en correlaciones
cruzadas con bines estrechos. Estimar la función de correlación angular es
particularmente costoso dado que el número de correlaciones cruzadas aumenta
como O(n^2), donde $n$ es el número de bines en redshift.
Más adelante, el capítulo estudia el efecto de aproximación de Limber, y RSD en
el modelado de correlaciones auto y cruzadas. Para bines de redshift delgados,
la aproximación de Limber deja de funcionar y no permite incorporar las
correlaciones cruzadas. Al disminuir el ancho de los bines en redshift, crece
la amplitude de correlacion y el efecto de RSD, lo que redundará en beneficio
del acotamiento de parametros cosmológicos. Una tendencia interesante es la
contribución de las oscilaciones acústicas de bariones (BAO) en la correlacion
cruzadas entre bines de distitnto redshift. La separacion en redshift entre dos
bines reduce la amplitud de las correlaciones en escalas pequeñas, lo que
aumenta el contraste en el BAO. También estudiamos la relación señal-ruido de
diferentes correlaciones cruzadas.
El segundo Capítulo presenta un pronóstico de cotas en la historia de la
expansión y del crecimiento cósmico, usando un catalogo spectroscópico y otro
fotométrico ficticios de 14000 grados cuadrados cada uno. Cuando estos
catalogos se sobrelapan en la misma region del cielo, encontramos mejores cotas
en los parametros cosmológicos. Esto es debido a las correlaciones cruzadas
adicionales entre catálogos y la reducción de la varianza en el muestreo
(debida a la covarianza entre trazadores). En primer lugar mostramos un estudio
por separado de la dependencia en el ancho de bin en redshift, en RSD, en BAO y
en WL. Encontramos ganancias equivalentes a tener el 30% mas de área en los
catalogos cuando estos se superponen en el cielo. Por último, analizamos el
origen de esta moderada ganancia en el contexto de la literatura existente.
Diferentes grupos han reportado que al solapar los catalogos o bien no
encuentran ningún beneficio o bien encuentran grandes beneficios. Nosotros
sugerimos que la covarianza entre observables y el uso de diferentes
observables puede explicar estas diferencias.
El sesgo (bias) en galaxias, relaciona las sobredensidades de galaxias con las
del campo de fluctuaciones de materia, de manera que la incertidumbre en el
bias limita las predicciones. Por ello investigamos con detalle como las
correlaciones cruzadas, RSD, BAO y WL afectan las medidas del bias en galaxias.
En particular, cuando los catalogos sobrelapan disminuyen los errores en el
bias para la muestras fotométrica. La última seccion cuantifica los
beneficios de los "priors'' y los efectos de la estocasticidad en el bias. El
impacto de las incertidumbres en las estocasticidad es menor cuando hay
sobrelapamiento.In this thesis we study constraining cosmology when combining spectroscopic and photometric galaxy survey. The photometric survey measures galaxy shape distortions from Weak Lensing (WL), while high precision redshift information makes spectroscopic surveys ideal for redshift space distortions (RSD). The combined analysis is performed entirely in angular-correlation functions, which simplifies the joined analysis, in particular the inclusion of covariance between then. The first chapter introduce a novel algorithm for efficiently calculating the cross-correlations of multiple tracers (i.e. galaxy types/luminosities) and including WL in narrow redshift bin cross-correlations. Estimating the angular-correlations function is in particular demanding since the number for cross-correlations increase O(n^2) with $n$ being the number of redshift bins. Later the chapter study the effect of Limber approximation and RSD on the modeling of auto- and cross-correlations. For thin redshift bins, the Limber approximation completely breaks down and does not allow cross-correlations between redshift bins. Decreasing the bin width increases the amplitude of the galaxy correlations and the effect of RSD, which will benefit the cosmological constraints. One interesting trend is the baryon acoustic oscillation (BAO) contribution in the cross-correlations of redshift bins. The redshift separations between two bins reduce small-scale clustering, hence increasing the BAO contrast. We also study the signal-to-noise of different cross-correlations. The second chapter forecast the constraints on the cosmic expansion and growth history, using two fiducial 14000 sq deg. spectroscopic and photometric galaxy surveys. Overlapping surveys (same sky) has improved constraints from additional cross-correlations and sample variance cancellations (covariance in multiple tracers). We study first separate how redshift bin width, RSD, BAO and WL affect the forecast. We find gains equivalent to 30\% larger areas when using overlapping surveys. Last, we discuss the origen of this moderate gain in the context of existing literature. Different groups reports either none or high benefits for overlapping galaxy surveys. We suggest the covariance between surveys and different same-sky definitions (i.e. different observables) can explain the differences. Galaxy bias relate the galaxy overdensities to the underlying matter fluctuations, and the uncertainty in galaxy bias strongly affects the forecast. We therefore investigate in detail how cross-correlations, RSD, BAO and WL affects constraints on galaxy bias. Overlapping surveys in particular increase constraint on the bias from the photometric sample. Last section quantify the benefit of priors and the effect of bias stochasticity. The impact of uncertainties in bias stochasticity is less for overlapping surveys.