Dissertations / Theses on the topic 'Dynamics of galaxies'

We use the positions and velocities of satellites of our galaxy and of other spiral galaxies to determine the radial mass profile of dark matter halos. We combine our measurement of the velocities of five remote Galactic satellites with published observations of the other Galactic satellites to obtain a complete sample of test particles. We then apply statistical techniques and timing arguments to deduce that the mass of the Galaxy is ≳ 1.3 x 10¹²M(⊙) for standard assumptions and that the halo extends beyond 100 kpc Galactocentric distance. We confirm our result by examining the dynamics of other Local Group galaxies. Subsequently, we expand our study to include nearby (1000 km s⁻¹ < ν(R) < 7000 km s⁻¹) Sb-Sc type galaxies. We use multiaperture spectrometers to conduct a survey for satellite galaxies and are able to double the sample of known satellite galaxies (satellites are defined to be at least eight times fainter than the primary) of isolated unbarred late-type spirals. The homogeneity of the primaries allows us to combine observations of satellites of various primaries and analyze the dynamical properties of the ensemble. The characteristics of this satellite sample (number, radial and azimuthal distribution, luminosity function, orbital characteristics, and contamination) are discussed. Finally, new models of the dynamics of satellite galaxies are developed that include the effects of the cosmological evolution of the halos and do not presume that halos are virialized. These models are used to constrain the mass distribution in which the satellite galaxies orbit. We conclude that only model halos with more than 10¹²M(⊙) within a galactocentric radius of 200 kpc are acceptable (90% confidence limit) for orbits of eccentricity < 0.9. The preferred models (60% confidence limit) are of halos with more than 1.6 x 10¹²M(⊙) within 200 kpc. Halos that formed in a universe with Ω = 1 also fall within the preferred range and have ∼ 3 x 10¹²M(⊙) within 200 kpc. In addition, we infer that the satellites’ orbital eccentricities are typically less than 0.9. These results, in conjunction with the results obtained for the halo of our galaxy, constitute convincing evidence for the existence of large (>200 kpc) and massive (> 10¹²M(⊙), M/L > 80) dark matter halos around isolated unbarred late-type spiral galaxies.

It has been customary practice in galactic dynamics to implicitly assume that the corresponding N-body problem is (near) integrable. After a review of some relevant ideas from non-linear dynamics, I discuss the evidence suggesting that the above assumption is not generally satisfied and the consequences of such a situation. Next, I discuss the characterization of such "chaotic" behaviour. A geometric method-which I argue is best suited for measuring the instability properties of N-body systems-is tested on systems of 231 particles integrated with high precision and displaying "obvious" instabilities like violent relaxation and collective processes. The predicted instability time-scales show good agreement with those inferred from the spatial evolution. As a further test I study closed systems which relax towards definite equilibrium states. The times of relaxation towards such states are then compared to the exponential instability time-scales in an attempt to identify the physical interpretation of the exponential instability that appears to be always present in N -body systems. As an application of the method, the variation of the exponential divergence time-scales in N -body Plummer models with particle number, rotation, softening, and central mass is studied. I also study the extent of chaotic behaviour in some non-axisymmetric but smooth potentials representing galaxies with triaxial halos. This is done with the aid of Liapunov exponents, Poincare maps, and stability analysis of resonant orbits. It is found that a significant amount of chaos is usually present and increases dramatically with the addition of rotating bar perturbations, or of central masses. The degree of instability may also depend on the presence of external noise. It is also shown that dissipative perturbations have the important effect of producing an inflow of matter to the central areas. The consequences of the above processes are then discussed and it is suggested that they may explain some aspects of the observed relative bulge-disk-halo contributions to galaxy rotation curves.

Lenticular and elliptical galaxies, collectively referred to as "early-type galaxies" (ETGs), are commonly thought to represent the end-points of galaxy evolution. Lying in the red sequence of galaxies, these objects are defined by their mostly old stellar populations and by their "red and dead" appearance in optical observations. Much progress in understanding these objects has been made with integral-field spectroscopy in recent years, with results repeatedly pointing to a link between early-type galaxies and high-redshift spiral galaxies. However, the exact nature of this link remains unclear, with a wide variety of evolution scenarios likely required to fully explain the range of observed early-type galaxy properties. In my study, I analysed observations of twelve early-type galaxies taken with the Mitchell Integral-Field Spectrograph at McDonald Observatory, Texas. These galaxies have previously been found to contain detectable quantities of neutral hydrogen gas, with ten out of the twelve displaying large-scale hydrogen disks. I extracted line-of-sight kinematics of the stellar and ionised gas components of these galaxies, and I used various modelling approaches to constrain their stellar population parameters as well as their three-dimensional mass structure in terms of both dark and visible components. An important feature of this study is the wide field of view of the spectroscopic observations, which reach beyond two half-light radii for almost all of the sample; this remains rare for integral-field unit (IFU) studies of ETGs, and so sets this study apart from most earlier works. The gas-rich nature of the sample is likewise novel. I find all aspects of my analysis to yield a consistent view of these galaxies' evolution, in which one or more gaseous interaction events served to shape them into their observed forms. I find these galaxies to contain low dark matter fractions on average within the inner half-light radius, and I also find mass modelling to favour near-isothermal total density profiles over much of the sample.

Since the 30's and Edwin Hubble's famous classification, galaxies are usually separated in twogroups : the late-type galaxies (LTGs) and the early-type galaxies (ETGs). The LTGs family ismainly made of spiral galaxies (S) while the ETGs family is composed of elliptical (E) and lenticular(S0) galaxies. A morphological study of all these galaxies revealed that around 60% of LTGs and45% of S0 present a bar. It has also been shown that, in the local Universe, galaxies fall into twobig groups : the blue cloud mostly populated by LTGs and the red sequence mainly made of ETGs.Several mechanisms are responsible for this distribution and the secular evolution is obviously animportant one to examine, sepcially in the context of bars, as an important number of studiesshowed the importance of bars in the dynamics and evolution of a galaxy.The goal of my thesis is to study the importance of the formation and ensued bar-drivenevolution influence on ETGs evolution. In that context, I have performed N-body simulations ofbarred (and unbarred) galaxies in order to investigate the following issues.First of all, I focused on the influence of a bar in a galaxy when modelling it with a dynamicalmodel assuming an axisymmetric mass distribution. As these kinds of models allow to determine themass-to-light ratio M/L, thus the dynamical mass of an observed galaxy, but also its inclinationand its anisotropy, it is important to evalute the consequence of the presence of a bar on theseparameters. I have shown that, depending on the galaxy inclination and the bar position angle,M/L is most of the time biased and overestimated, and this can be up to 25%. The size andstrength of the bar also seem to be important factors but a deeper study has to be done to quantifythis preliminary result.In a second step, I have studied the role of bars on the mass and metallicity redistributionsin a lenticular galaxy. I confirmed that the presence of a bar, due to its influence on its hostsystem dynamics, flattens pre-existing metallicity gradients. Moreover, I showed that the degree offlattening and the position of affected regions are directly correlated with the bar structure and thelocation of the dynamical resonances. Nonetheless, this dynamical effect cannot explain the varietyof observed ages and metallicity gradients. The consequences of a barred gravitational potentialon the gas dynamics and the stellar formation should therefore be investigated. This is the topicof the last set of numerical simulations produced which will allow to better understand the globalinfluence a bar has on the secular evolution of ETGs.

A scaling relation between the surface density of star formation and gas in the disks of galaxies has become the basis of our understanding of extragalactic star formation on scales of hundreds of parsecs and larger. This is an empirical law but star formation is a complex process - the presence of gas at sufficiently high densities to collapse and form stars depends on a wide variety of physical processes. These processes can be thought of in terms of the stability of galaxy disks, which is a balance between the gravitational force and competing forces such as the outward force due to pressure. In this study I explore how star formation is related to galaxy dynamics in the central regions of galaxies. This is done by determining the dominant contributor to the inner dynamics of galaxies and developing star formation models based on self-regulating disks that maintain a constant sub-critical stability parameter. Stability parameters for a gas-only disk and a two- uid disk containing both gas and stars are considered. These models are tested in the central regions of a sample of galaxies with a wide range of Hi masses, sizes, morphologies and stellar masses. The analysis is performed using Hα integral field spectroscopy, R-band, narrowband Hα, and near-infrared photometry to determine the star formation rates and kinematics of the galaxies. In agreement with previous studies I find that the central stellar surface density is tightly correlated with the central velocity gradient, which traces the steepness of the inner gravitational well. The baryonic fractions found in the analysis suggest that baryons dominate the central density of most galaxies in the sample, but better constraints on these are needed to make more firm conclusions. There are correlations between the star formation surface density and velocity gradient, however the observed relations do not match predictions from the models. Tests suggest that the failure of the models is due to the implied stability parameters in the galaxy centers not being constant across the galaxy sample, and that the star formation laws used in the analysis may not hold over the full parameter space of the sample.

This Thesis studies the dynamics of hot and cold gas outside the plane in galaxies like the Milky-Way (extra-planar gas) and focuses on the interaction between disc and halo material. Stationary models for the cold phase of the extra-planar gas are presented. They show that the kinematics of this phase must be influenced by the interaction with an ambient medium that we identify as the hot cosmological corona that surrounds disc galaxies. To study this interaction a novel hydrodynamical code has been implemented and a series of hydrodynamical simulations has been run to investigate the mass and momentum exchange between the cold extra-planar gas clouds and the hot corona. These simulations show that the coronal gas can condense efficiently in the turbulent wakes that form behind the cold clouds and it can be accreted by the disc to sustain star formation. They also predict that the corona cannot be a static structure but it must rotate and lag by approximately 80-120 km/s with respect to the disc. Implications of the results of this Thesis for the evolution of star-forming galaxies and for the large-scale dynamics of galactic coronae are also briefly discussed.

This Thesis studies the dynamics of hot and cold gas outside the plane in galaxies like the Milky-Way (extra-planar gas) and focuses on the interaction between disc and halo material. Stationary models for the cold phase of the extra-planar gas are presented. They show that the kinematics of this phase must be influenced by the interaction with an ambient medium that we identify as the hot cosmological corona that surrounds disc galaxies. To study this interaction a novel hydrodynamical code has been implemented and a series of hydrodynamical simulations has been run to investigate the mass and momentum exchange between the cold extra-planar gas clouds and the hot corona. These simulations show that the coronal gas can condense efficiently in the turbulent wakes that form behind the cold clouds and it can be accreted by the disc to sustain star formation. They also predict that the corona cannot be a static structure but it must rotate and lag by approximately 80-120 km/s with respect to the disc. Implications of the results of this Thesis for the evolution of star-forming galaxies and for the large-scale dynamics of galactic coronae are also briefly discussed.

We present new Atacama Large Millimeter/submillimeter Array (ALMA) observations of the dust continuum and [C II] 158 mu m fine structure line emission toward a far-infrared-luminous quasar, ULAS J131911.29+095051.4 at z = 6.13, and combine the new Cycle 1 data with ALMA Cycle 0 data. The combined data have an angular resolution of similar to 0.'' 3, and resolve both the dust continuum and the [C II] line emission on a few kiloparsec scales. The [C II] line emission is more irregular than that of the dust continuum emission, which suggests different distributions between the dust and the [C II] emitting gas. The combined data confirm the [C II] velocity gradient that we had previously detected in a lower-resolution ALMA image from the Cycle 0 data alone. We apply a tilted ring model to the [C II] velocity map to obtain a rotation curve, and constrain the circular velocity to be 427 +/- 55 kms(-1) at a radius of 3.2 kpc with an inclination angle of 34 degrees. We measure the dynamical mass within the 3.2 kpc region to be 13.4(-5.3)(+7.8) x 10(10) M-circle dot. This yields a black-hole and host galaxy mass ratio of 0.020(-0.007)(+0.013), which is about 4(-2)(+3) times higher than that of the present-day M-BH/M-bulge ratio. This suggests that the supermassive black hole grows the bulk of its mass before the formation of most of the stellar mass in this quasar host galaxy in the early universe.

We present a recalibration of the M-BH-sigma(star) relation, based on a sample of 16 reverberation-mapped galaxies with newly determined bulge stellar velocity dispersions (sigma(star)) from integral-field spectroscopy (IFS), and a sample of 32 quiescent galaxies with publicly available IFS. For both samples, sigma(star) is determined via two different methods that are popular in the literature, and we provide fits for each sample based on both sets of sigma(star). We find the fit to the active galactic nucleus sample is shallower than the fit to the quiescent galaxy sample, and that the slopes for each sample are in agreement with previous investigations. However, the intercepts to the quiescent galaxy relations are notably higher than those found in previous studies, due to the systematically lower sigma(star) measurements that we obtain from IFS. We find that this may be driven, in part, by poorly constrained measurements of bulge effective radius (r(e)) for the quiescent galaxy sample, which may bias the sigma(star) measurements low. We use these quiescent galaxy parameterizations, as well as one from the literature, to recalculate the virial scaling factor f. We assess the potential biases in each measurement, and suggest f = 4.82 +/- 1.67 as the best currently available estimate. However, we caution that the details of how sigma(star) is measured can significantly affect f, and there is still much room for improvement.

We explore the evolution of the internal gas kinematics of star-forming galaxies from the peak of cosmic star formation at z similar to 2 to today. Measurements of galaxy rotation velocity V-rot, which quantify ordered motions, and gas velocity dispersion sigma(g), which quantify disordered motions, are adopted from the DEEP2 and SIGMA surveys. This sample covers a continuous baseline in redshift over 0.1 < z < 2.5, spanning 10 Gyr. At low redshift, nearly all sufficiently massive star-forming galaxies are rotationally supported (V-rot > sigma(g)). By z = 2, 50% and 70% of galaxies are rotationally supported at low (10(9)-10(10) M-circle dot) and high (10(10)-10(11) M-circle dot) stellar mass, respectively. For V-rot > 3 sigma(g), the percentage drops below 35% for all masses. From z = 2 to now, galaxies exhibit remarkably smooth kinematic evolution on average. All galaxies tend toward rotational support with time, and higher-mass systems reach it earlier. This is largely due to a mass-independent decline in sigma(g) by a factor of 3 since z - 2. Over the same time period, V-rot increases by a factor of 1.5 in low-mass systems but does not evolve at high mass. These trends in V-rot and sigma(g) are at a fixed stellar mass and therefore should not be interpreted as evolutionary tracks for galaxy populations. When populations are linked in time via abundance matching, sigma(g) declines as before and V-rot strongly increases with time for all galaxy populations, enhancing the evolution in V-rot sigma(g). These results indicate that z = 2 is a period of disk assembly, during which strong rotational support is only just beginning to emerge.

The formation and evolution of galaxies is studied using two alternative modelling techniques within the context of the LCDM cosmogony. In particular, we consider the capacity of the models to reproduce the fundamental components and internal structure of galaxies. We begin by outlining the theoretical basis for the study, describing the standard paradigm for structure formation and the details of the modelling techniques we employ. The extent of our current understanding of the processes responsible for morphological transformation is explored and we discuss what the structure of the Milky Way and its satellites can reveal about the wider pictures of galaxy formation and cosmology. Using data from two semi-analytical models, we investigate the origin of the disks and spheroids that represent the coarse-grain detail of galactic structure. Major galaxy mergers, which have long been regarded as the main mechanism by which elliptical galaxies and spiral bulges are generated, are found to play only a minor role in spheroid formation for all but the most massive systems. The models make similar predictions in many respects but disagree on the importance of gravitationally unstable disks in forming spheroids, serving to illustrate the uncertainty that remains in modelling morphology even at this basic level. We go on to introduce a smoothed particle hydrodynamics code which includes models for radiative gas heating and cooling, the structure of the interstellar medium, star formation and evolution, chemical enrichment and feedback from supernovae. We present a set of simulations that focus on a single Milky Way-mass galaxy and its local environment and summarise its bulk properties and formation history. We also show results from a code comparison project, which aims to quantify the effects of different physical mechanisms and modelling approaches on the formation of a galaxy disk. Our simulations also resolve the formation of a population of satellite galaxies which have a luminosity function similar to those found around the Milky Way. Through comparison with a dissipationless version of the same simulation, we determine that the baryonic component in each satellite has little effect on the structure of its dark matter halo. We also find a statistically significant discrepancy between the central mass densities of the simulated and observed satellites. Finally, we consider the formation of the haloes of hot gas and stars which surround the main galaxy disk. We find qualitative agreement with several observed properties of the Milky Way's stellar halo and with recent theoretical studies of the two components in the literature.

In this thesis, I use the new generation of radio interferometer along with X-ray observations to investigate the dynamics and energetics of radio-loud active galaxies which are key to understanding AGN feedback and the evolution of galaxies as a whole. I present new JVLA observations of powerful radio source and use innovative techniques to undertake a detailed analysis of JVLA observations of powerful radio galaxies. I compare two of the most widely used models of spectral ageing, the Kardashev-Pacholczyk and Jaffe-Perola models and also results of the more complex, but potentially more realistic, Tribble model. I find that the Tribble model provides both a good fit to observations as well as providing a physically realistic description of the source. I present the first high-resolution spectral maps of the sources and find that the best-fitting injection indices across all models take higher values than has previously been assumed. I present characteristic hot spot advance speeds and compare them to those derived from dynamical ages, confirming that the previously known discrepancy in speed remains present in older radio sources even when ages are determined at high spectral and spatial resolutions. I show that some previously common assumptions made in determining spectral ages with narrow-band radio telescopes may not always hold. I present results from a study of the powerful radio galaxy 3C223 at low frequencies with LOFAR to determine its spectrum on spatially small scales and tightly constrain the injection index, which I find to be consistent with the high values found at GHz frequencies. Applying this new knowledge of the low energy electron population, I perform synchrotron / inverse-Compton model fitting and find that the total energy content of the radio galaxy lobes increases by a factor greater than 2 compared to previous studies. Using this result to provide revised estimates of the internal pressure, I find the northern lobe to be in pressure balance with the external medium and the southern lobe to be overpressured. I go on to present the first large sample investigation of the properties of jets in Fanaroff and Riley type I radio galaxies (FR-I) at X-ray energies based on data from the Chandra archive. I explore relations between the properties of the jets and the properties of host galaxies in which they reside. I find previously unknown correlations to exist, relating photon index, volume emissivity, jet volume and luminosity, and find that the previously held assumption of a relationship between luminosities at radio and X-ray wavelengths is linear in nature when bona fide FR-I radio galaxies are considered. In addition, I attempt to constrain properties which may play a key role in determination of the diffuse emission process. I test a simple model in which large-scale magnetic field variations are primarily responsible for determining jet properties; however, we find that this model is inconsistent with our best estimates of the relative magnetic field strengths in my sample.

Cosmological N-body simulations indicate that the dark matter haloes of galaxies should be generally triaxial. Yet, the presence of a baryonic disc is believed to modify the shape of the haloes. The goal of this thesis is to study how bar formation is affected by halo triaxiality and how, in turn, the presence of the bar influences the shape of the halo. We performed a series of collisionless and hydrodynamical numerical simulations, using elliptical discs as initial conditions. Triaxial halos tend to become more spherical and we show that part of the circularisation of the halo is due to disc growth, but part must be attributed to the formation of a bar. We find that the presence of gas in the disc is a more efficient factor than halo triaxiality in inhibiting the formation of a strong bar.<br>As simulações cosmológicas de N-corpos indicam que os halos de matéria escura das galáxias devem ser em geral triaxiais. Contudo, acredita-se que a presença de um disco bariônico seja capaz de alterar a forma do halo. O objetivo desta tese é o de estudar como a formação de barras é afetada pela triaxialidade do halo e como, por sua vez, a presença da barra influencia a forma do halo. Nós realizamos uma série de simulações numéricas acolisionais e hidrodinâmicas, utilizando discos elípticos como condições iniciais. Os halos triaxiais tendem a se tornar mais esféricos e nós mostramos que parte da circularização do halo é devida ao crescimento do disco, mas parte precisa ser atribuída à formação da barra. Notamos que a presença de gás no disco é um fator mais eficiente do que a triaxialidade do halo em inibir a formação de uma barra forte.

Des simulations cosmologiques à N-corps indiquent que les halos de matière noire des galaxies devraient être généralement triaxiaux. Pourtant, on croit que la présence d’un disque baryonique modifie la forme des halos. L’objectif de cette thèse est d’étudier comment la formation des barres est affectée par la triaxialité des halos et comment, à son tour, la présence de la barre influence la forme du halo. Nous réalisons un ensemble de simulations numériques non-collisionnelles et hydrodynamiques, utilisant des disques elliptiques comme conditions initiales. Les halos triaxiaux ont tendance à devenir plus sphérique et nous montrons qu’une partie de la circularisation du halo est due à la croissance du disque, mais une partie doit être attribuée à la formation d’une barre. Nous trouvons que la présence du gaz dans le disque est un facteur plus efficace que la triaxialité du halo pour inhiber la formation d’une barre forte<br>Cosmological N-body simulations indicate that the dark matter haloes of galaxies should be generally triaxial. Yet, the presence of a baryonic disc is believed to modify the shape of the haloes. The goal of this thesis is to study how bar formation is affected by halo triaxiality and how, in turn, the presence of the bar influences the shape of the halo. We performed a series of collisionless and hydrodynamical numerical simulations, using elliptical discs as initial conditions. Triaxial halos tend to become more spherical and we show that part of the circularisation of the halo is due to disc growth, but part must be attributed to the formation of a bar. We find that the presence of gas in the disc is a more efficient factor than halo triaxiality in inhibiting the formation of a strong bar

This paper provides an update of our previous scaling relations between galaxy-integrated molecular gas masses, stellar masses, and star formation rates (SFRs), in the framework of the star formation main sequence (MS), with the main goal of testing for possible systematic effects. For this purpose our new study combines three independent methods of determining molecular gas masses from CO line fluxes, far-infrared dust spectral energy distributions, and similar to 1 mm dust photometry, in a large sample of 1444 star-forming galaxies between z = 0 and 4. The sample covers the stellar mass range log(M-*/M-circle dot) = 9.0-11.8, and SFRs relative to that on the MS, delta MS = SFR/SFR (MS), from 10(-1.3) to 10(2.2). Our most important finding is that all data sets, despite the different techniques and analysis methods used, follow the same scaling trends, once method-to-method zero-point offsets are minimized and uncertainties are properly taken into account. The molecular gas depletion time t(depl), defined as the ratio of molecular gas mass to SFR, scales as (1 + z)(-0.6) x (delta MS)(-0.44) and is only weakly dependent on stellar mass. The ratio of molecular to stellar mass mu(gas) depends on (1+ z)(2.5) x (delta MS)(0.52) x (M-*)(-0.36), which tracks the evolution of the specific SFR. The redshift dependence of mu(gas) requires a curvature term, as may the mass dependences of t(depl) and mu(gas). We find no or only weak correlations of t(depl) and mu(gas) with optical size R or surface density once one removes the above scalings, but we caution that optical sizes may not be appropriate for the high gas and dust columns at high z.

We present results from a survey of the internal kinematics of 49 star-forming galaxies at z similar to 2 in the CANDELS fields with the Keck/MOSFIRE spectrograph, Survey in the near-Infrared of Galaxies with Multiple position Angles (SIGMA). Kinematics (rotation velocity V-rot and gas velocity dispersion sg) are measured from nebular emission lines which trace the hot ionized gas surrounding star-forming regions. We find that by z similar to 2, massive star-forming galaxies (log M-*/M-circle dot less than or similar to 10.2) have assembled primitive disks: their kinematics are dominated by rotation, they are consistent with a marginally stable disk model, and they form a Tully-Fisher relation. These massive galaxies have values of V-rot sg that are factors of 2-5 lower than local well-ordered galaxies at similar masses. Such results are consistent with findings by other studies. We find that low-mass galaxies (log M-*/M-circle dot less than or similar to 10.2) at this epoch are still in the early stages of disk assembly: their kinematics are often dominated by gas velocity dispersion and they fall from the Tully-Fisher relation to significantly low values of V-rot. This "kinematic downsizing" implies that the process(es) responsible for disrupting disks at z similar to 2 have a stronger effect and/or are more active in low-mass systems. In conclusion, we find that the period of rapid stellar mass growth at z similar to 2 is coincident with the nascent assembly of low-mass disks and the assembly and settling of high-mass disks.

We describe how to estimate the velocity dispersions of ultradiffuse galaxies (UDGs) using a previously defined galaxy scaling relationship. The method is accurate for the two UDGs with spectroscopically measured dispersions, as well as for ultracompact galaxies, ultrafaint galaxies, and stellar systems with little or no dark matter. This universality means that the relationship can be applied without further knowledge or prejudice regarding the structure of a galaxy. We then estimate the velocity dispersions of UDGs drawn from two published samples and examine the distribution of total masses. We find, in agreement with the previous studies of two individual UDGs, that these systems are dark matter dominated systems, and that they span a range of at least 10(10) < M-200/M-circle dot < 10(12). These galaxies are not, as an entire class, either all dwarfs or all failed L-* galaxies. Estimates of the velocity dispersions can also help identify interesting subsets of UDGs, such as those that are likely to have the largest mass-to-light ratios, for subsequent spectroscopic study.

In this paper, we introduce the Local Volume TiNy Titans sample (LV-TNT), which is a part of a larger body of work on interacting dwarf galaxies: TNT . This LV-TNT sample consists of 10 dwarf galaxy pairs in the Local Universe (< 30 Mpc from Milky Way), which span mass ratios of M-*,M- 1/M-*,M- 2 < 20, projected separations < 100 kpc, and pair member masses of log(M-*/M-aS (TM)) < 9.9. All 10 LV-TNT pairs have resolved synthesis maps of their neutral hydrogen, are located in a range of environments and captured at various interaction stages. This enables us to do a comparative study of the diffuse gas in dwarf-dwarf interactions and disentangle the gas lost due to interactions with haloes of massive galaxies, from the gas lost due to mutual interaction between the dwarfs. We find that the neutral gas is extended in the interacting pairs when compared to non-paired analogues, indicating that gas is tidally pre-processed. Additionally, we find that the environment can shape the H i distributions in the form of trailing tails and that the gas is not unbound and lost to the surroundings unless the dwarf pair is residing near a massive galaxy. We conclude that a nearby, massive host galaxy is what ultimately prevents the gas from being re-accreted. Dwarf-dwarf interactions thus represent an important part of the baryon cycle of low-mass galaxies, enabling the 'parking' of gas at large distances to serve as a continual gas supply channel until accretion by a more massive host.

Using a sample of nearly half a million galaxies, intersected by over 7 million lines of sight from the Sloan Digital Sky Survey Data Release 12, we trace H alpha + [N II] emission from a galactocentric projected radius, r(p), of 5 kpc to more than 100 kpc. The emission flux surface brightness is alpha r(p) 1.9 +/- 0.4. We obtain consistent results using only the Ha or [N II] flux. We measure a stronger signal for the bluer half of the target sample than for the redder half on small scales, r(p) < 20 kpc. We obtain a 3 sigma detection of H alpha + [N II] emission in the 50-100 kpc r(p) bin. The mean emission flux within this bin is (1.10 +/- 0.35) x 10(-20) erg cm(-2) s(-1) angstrom(-1), which corresponds to 1.87 x 10(-20) erg cm(-2) s(-1) arcsec(-2) or 0.0033 Rayleigh. This detection is 34 times fainter than a previous strict limit obtained using deep narrow-band imaging. The faintness of the signal demonstrates why it has been so difficult to trace recombination radiation out to large radii around galaxies. This signal, combined with published estimates of n(H), leads us to estimate the temperature of the gas to be 12,000 K, consistent with independent empirical estimates based on metal ion absorption lines and expectations from numerical simulations.

We conducted a large spectroscopic survey of 336 red giants in the direction of the Leo II dwarf galaxy using Hectochelle on the Multiple Mirror Telescope, and we conclude that 175 of them are members based on their radial velocities and surface gravities. Of this set, 40 stars have never before been observed spectroscopically. The systemic velocity of the dwarf is 78.3 +/- 0.6 km s(-1) with a velocity dispersion of 7.4 +/- 0.4 km s(-1). We identify one star beyond the tidal radius of Leo II but find no signatures of uniform rotation, kinematic asymmetries, or streams. The stars show a strong metallicity gradient of -1.53 +/- 0.10 dex kpc(-1) and have a mean metallicity of -1.70 +/- 0.02 dex. There is also evidence of two different chemodynamic populations, but the signal is weak. A larger sample of stars would be necessary to verify this feature.

We present a chemodynamical analysis of the Leo V dwarf galaxy, based on the Keck II DEIMOS spectra of eight member stars. We find a systemic velocity for the system of nu(r) = 170.9(+2.1) (-1.9) km s(-1) and barely resolve a velocity dispersion for the system, with sigma nu(r) = 2.3(+3.2) (-1.6) km s(-1), consistent with previous studies of Leo V. The poorly resolved dispersion means we are unable to adequately constrain the dark-matter content of Leo V. We find an average metallicity for the dwarf of [ Fe/ H] =-2.48 +/- 0.21 and measure a significant spread in the iron abundance of its member stars, with -3.1 <= [ Fe/ H] <=-1.9 dex, which clearly identifies Leo V as a dwarf galaxy that has been able to self-enrich its stellar population through extended star formation. Owing to the tentative photometric evidence for the tidal substructure around Leo V, we also investigate whether there is any evidence for tidal stripping or shocking of the system within its dynamics. We measure a significant velocity gradient across the system, of dv d chi = -4.1(+2.8) (-2.6) km s(-1) arcmin(-1) ( or d nu/d chi=-71.9(vertical bar 50.8) (-45.6) km s(-1) kpc(-1)), which points almost directly towards the Galactic Centre. We argue that Leo V is likely a dwarf on the brink of dissolution, having just barely survived a past encounter with the centre of the Milky Way.

In this thesis we focused on the determination of the mass (MBH) of supermassive black hole (SMBHs) and on the interpretation of their demography. We studied their scaling relations with the aim of understanding the role of SMBHs in the evolution of galaxies. This was done by increasing the demography of MBH and studying whether MBH results more closely linked to the bulge or to the global galaxy properties, including the dark matter halo. In the first part of the thesis we focused on the presentation of a spectral and imaging atlas of a large and various sample of galaxies we studied to obtain upper limits on their MBH. The data were retrieved from Hubble Space Telescope (HST) archive (Chapter 2). This atlas comprises of 177 nearby galaxies (D < 100 Mpc) with nuclear spectra obtained with the Space Telescope Imaging Spectrograph (STIS) in the region of Halpha line and the [NII] and [SII] emission-line doublets. Structural parameters of bulge and disk derived from the two-dimensional bulge-to-disk decompositions of K-band 2MASS and UKIDSS images for 65 sample galaxies are presented, too. We derived stringent upper bounds on the mass of the central SMBH for a sub-sample of 105 galaxies spanning a wide range of Hubble types (E-Sc) and values of the central stellar velocity dispersion, sigma (58-419 km/s). These MBH upper limits were derived by modeling the widths of the observed emission lines in terms of gas motions in a thin disk of unknown orientation but known spatial extent. The upper limits that we derived are consistent with both the MBH-sigma relation of Ferrarese & Ford (2005, Sp. Sci. Rev., 116, 523) and Lauer et al. (2007, ApJ, 670, 249) and with secure MBH determinations. Most important, independent of the galaxy distance, morphological type or bar presence, our MBH upper limits run parallel and above the previous two version of MBH-sigma relations. This suggests that, although strictly speaking we cannot rule out the role of non-gravitational forces, our line-width measurements actually trace well the nuclear regions dominated by the central SMBH, which in practice allows us to estimate MBH (Chapter 3). Yet, at small sigma some MBH upper limits systematically exceed the expected MBH, as the line-width measurements for such low-sigma outliers are most likely affected by the stellar contribution to the gravitational potential either due to the presence of conspicuous nuclear clusters or because of a greater distance compared to the other galaxies at the low-sigma end of the MBH-sigma relation. Conversely, the MBH upper bounds appear to lie closer to the expected MBH in the most massive elliptical galaxies with values sigma>220 km/s. Such a flattening of the MBH-sigma relation at its high-sigma end would appear consistent with a coevolution of SMBHs and galaxies driven by dry mergers, although better and more consistent measurements for sigma and K-band luminosity are needed for these kinds of objects before systematic effects can be ruled out. Following these results we focused on the interpretation of the demography of SMBHs, specifically in trying to understand whether the MBH relates more closely to the bulge or to the total mass of a galaxy (Chapter 4). The large sample of upper limits on MBH and the latest compilation of secure MBH, coupled with libraries of host galaxy velocity dispersions, rotational velocities and photometric parameters extracted from SDSS i-band images were used to establish correlations between MBH and the properties of the bulge and of the host galaxy. We tested the correlations between MBH and stellar velocity dispersion, i-band bulge luminosity, bulge virial mass, bulge Sersic index, total i-band luminosity of the galaxy, galaxy stellar mass, maximum circular velocity, and galaxy dynamical and virial masses. The tightness of the MBH-sigma relation was derived, and it resulted that correlations with other galaxy parameters do not yield tighter trends. MBH is fundamentally driven by sigma for all Hubble types. The fundamental plane of the SMBHs is mainly driven by sigma too, with a small fraction of the tilt being due to the effective radius. We explored the high-mass end of the SMBH mass function to understand the link between the evolution of SMBHs and the hierarchical build-up of galaxies, by measuring MBH in the massive elliptical galaxy NGC1265 with adaptive-optics stellar observations (Chapter 5) and in three brightest cluster galaxies from the gaseous kinematics derived from HST data (Chapter 6). These works are important to understand the MBH distribution at high sigma, where different works found either a flattening or a steepening of the MBH-sigma relation. We presented the K-band adaptive-optics assisted spectroscopic observations of the central region of the archetype head-tail radio galaxy NGC 1265/3C 83.1B with the aim of constraining the mass of its SMBH (Chapter 5). The near-infrared data taken with the Altair/NIRI on the Gemini North have a spatial resolution of FWHM = 0''.11 (39 pc). To account for the stellar contribution, we performed a multi-Gaussian expansion by using a combination of our NIRI high-resolution K-band image and a TNG K'-band image to cover the outer parts of the galaxy. We extracted the stellar kinematics by using the penalized pixel fitting method from the CO absorption bands at 2.29 microns. Jeans anisotropic models were adopted to fit the stellar kinematics and surface distribution to determine the best fitting value for anisotropy and MBH. The limited quality of our kinematical data did not allow us to measure very extended kinematics. Hence, we resorted to assuming fixed values for both the (M/L)_K and the anisotropy, beta. The derived upper limit on MBH ranges between 1x 10e9 Msun and 3.45 x 10e9 Msun depending on the assumed values of beta and (M/L)_K, respectively. This range of masses is consistent with the MBH-Lk relation of Marconi & Hunt (2003, ApJ, 589, L21). We derived MBH in three brightest cluster galaxies (BCGs), Abell 1836-BCG, Abell 2052-BCG, and Abell 3565-BCG, by using observations with STIS, Wide Field and Planetary Camera 2 (WFPC2), and Advanced Camera for Surveys (ACS) on HST (Chapter 6). The data provided detailed information on the structure and mass profile of the stellar component, dust optical depth, and spatial distribution and kinematics of the ionized gas within the innermost region of each galaxy. Dynamical models, which account for the observed stellar mass profile and include the contribution of a central SMBH were constructed to reproduce the kinematics derived from the [NII] emission line. Secure SMBH detection with MBH = 3.61 (+0.41,-0.50) x 10e9 Msun and 1.34 (+021,-0.19) x 10e9 Msun, respectively, were obtained for Abell 1836-BCG and Abell 3565-BCG, which show regular rotation curves and strong central velocity gradients. In the case of Abell 2052-BCG, the lack of an orderly rotational motion prevented a secure determination, although an upper limit of MBH < 4.60 x 10e9 Msun could be placed on the mass of the central black hole. These measurements are an important step forward in characterizing the high-mass end of the SMBH mass function. In fact, the results suggest a steepening of the trend of the MBH-sigma relation in the high-sigma range, that suggest either a higher scatter or the necessity of a different law, which predicts a faster grow of the SMBH with respect to the sigma. Finally, we estimated the mass of the SMBH of NGC 4278 by using the virial theorem and measuring the broad components of the emission lines observed in the STIS spectrum, assuming that the gas is uniformly distributed in a sphere of radius R. The MBH is found to be in the range between 7 x 10e7 and 2 x 10e9 Msun depending on the radius we obtained from simple estimation of the dimension of the broad line region (Chapter 7). This is in agreement with previous findings based on different assumptions about the gas distribution. The nucleus of NGC 4278 hosts a barely resolved but strongly variable UV source. Its UV luminosity increased by a factor of 1.6 in a period of 6 months. The amplitude and scale time of this UV flare are remarkably similar to those of the brightest UV nuclear transients which were earlier found in other low-luminosity AGNs. This ultraviolet variability represents the typical signatures of the low-luminosity active galactic nuclei. The main conclusions of this thesis can be summarized as follows. 1) We could map the MBH-sigma relation from the lower to the upper end of the local SMBH population by using simple estimates of MBH but for the largest and most various sample of host galaxies. These MBH estimates are consistent with the known MBH-sigma relation, with no dependence on galaxy distance, morphological type or bar presence. They can be adopted to study the trend and scatter of the other MBH scaling relations. 2) Following the results of this work we focused on the interpretation of the demography of SMBHs, specifically in trying to understand whether the MBH relates more closely to the mass of the bulge or to the total mass of the host galaxy, included dark matter. We confirmed that MBH is fundamentally driven by sigma for all Hubble types. The same is true for the fundamental plane of SMBHs. 3) We explored the high-mass end of the SMBH mass function to understand the link between the evolution of SMBHs and the hierarchical build-up of galaxies, by analyzing adaptive-optics stellar observations of the central regions of massive elliptical galaxies such us NGC 1265 and estimating MBH in three brightest cluster galaxies by measuring the gaseous kinematics with HST. The first results indicates a steepening of the trend of the MBH-sigma relation in the high-sigma range, that suggests either a higher scatter or the necessity of a different law, which predicts a faster grow of the SMBH with respect to sigma.<br>Questa tesi è dedicata alla misura della massa MBH dei buchi neri supermassicci (SMBH) e allo studio delle relazioni di scala tra le masse dei buchi neri e le proprietà delle galassie ospiti con lo scopo di capire il ruolo dei SMBH nell'evoluzione delle galassie. La prima parte della tesi è dedicata alla presentazione di un atlante di spettri e immagini di un ampio campione di galassie lungo tutta la sequenza morfologica di Hubble, il quale e' stato selezionato per misurare MBH (Capitolo 2). Gli spettri sono stati estratti dall'archivio di Hubble Space Telescope (HST). Il campione comprende 177 galassie vicine D <100 Mpc con spettro nucleare ottenuto con lo Space Telescope Imaging Spectrograph (STIS) nell'intervallo spettrale che include le righe di emissione di [NII], Halpha e [SII]. Per 65 galassie è stato inoltre possibile misurare i parametri strutturali del sferoide e dello disco ottenuti attraverso la decomposizione fotometrica bidimensionale di immagini 2MASS e UKIDSS in banda K. Sono stati ottenuti dei robusti limiti superiori della MBH per un sottocampione di 105 galassie (Capitolo 3) di diversi tipi morfologici (E-Sc) e con diverse dispersioni di velocita' stellare sigma (58-419 km/s). Questi limiti superiori sono stati misurati dalla larghezza delle righe di emissione, assumendo che il gas ionizzato delle regioni nucleari risieda in un disco sottile di orientazione incognita ma di cui si conosce l'estensione spaziale. I limiti superiori di MBH sono consistenti con le relazioni MBH-sigma di Ferrarese & Ford (2005, Sp. Sci. Rev., 116, 523) e Lauer et al. (2007, ApJ, 670, 249) e con le determinazioni accurate di MBH dei SMBH di cui è stata risolta la sfera d'influenza. Inoltre, questi limiti superiori di MBH si dispongono parallelamente e in prossimita' della relazione MBH-sigma senza mostrare alcuna dipendenza dalla distanza degli oggetti, dal loro tipo morfologico e dalla presenza o meno di una barra. Questo significa che la larghezza delle righe di emissione rappresenta un buon tracciante del potenziale gravitazionale del buco nero. Inoltre, il grande numero di galassie, che abbiamo a disposizione, permette di escludere che le larghezze delle righe siano dovute al solo contributo delle forze non gravitazionali. Tuttavia, per valori di sigma inferiori ai 90 km/s metà dei limiti superiori eccedono sistematicamente il valore previsto dalla relazione MBH-sigma. Questa peculiarità è stata imputata al maggior contributo stellare sul potenziale gravitazionale dovuto alla presenza di ammassi stellari nucleari e alla maggiore distanza dell'oggetto. Ad alte dispersioni di velocità (sigma>220km/s) i valori di MBH sembrano concordare con i valori attesi, soprattutto per le galassie ellittiche giganti, suggerendo un appiattimento della relazione MBH-sigma. Questo fenomeno potrebbe essere dovuto al meccanismo di coevoluzione con le galassie ospiti attraverso fenomeni di interazione e fusioni in assenza di gas. Tuttavia misure più precise di sigma e luminosità in banda K sono necessarie per escludere definitivamente gli eventuali effetti sistematici. Con i risultati ottenuti si e' visto come i limiti superiori della MBH possano essere utilizzati nel confronto con le relazioni di scala (Capitolo 4). Pertanto, sono stati usati per interpretare la demografia dei SMBH, in particolare per capire se MBH risulta più strettamente connessa con il solo sferoide o con l'intera galassia. A questo scopo i limiti superiori della MBH sono stati combinati con le MBH la cui sfera di influenza e' nota per essere stata risolta. Sono stati poi raccolti i dati relativi alle dispersioni di velocità e alle velocità circolari e sono stati misurati i parametri fotometrici dall'analisi delle immagini SDSS in banda i. Sono state considerate le correlazioni tra la MBH e la dispersione di velocità stellare, la luminosità in banda i, la massa viriale e l'indice di Sersic dello sferoide, la luminosità, la massa stellare, la velocità circolare e le masse viriale e dinamica della galassia. E' stata confermato che la relazione MBH-sigma risulta la piu' stretta tra tutte le correlazioni. La MBH risulta principalmente correlata con sigma per tutti i tipi morfologici e, analogamente, il piano fondamentale dei SMBH dipende principalmente da sigma con un piccolo contributo dovuto al raggio efficace. E' stata caratterizzata la parte alta della funzione di massa dei SMBH dell'universo locale, dal momento che è proprio alle masse più alte che il legame tra l'evoluzione dei SMBH e la formazione gerarchica delle galassie e' piu' stringente. Questo è stato fatto misurando la MBH in una galassia ellittica molto massiccia, NGC 1265, usando dati della cinematica stellare ottenuti con ottica adattiva (Capitolo 5) e stimando la MBH in tre galassie molto brillanti attraverso la cinematica del gas derivata da dati di HST (Capitolo 6). Queste misure sono importanti per capire l'andamento della relazione MBH-sigma nella regione ad alte sigma. Sono state analizzati dati spettroscopici della regione centrale della radio galassia NGC 1265/3C 83.1B (Capitolo 5). Gli spettri sono stati ottenuti in banda K al telescopio Gemini Nord con lo spettrografo Near InfraRed Imager and Spectrograph (NIRI) accoppiato con il sistema di ottica adattiva Altair permettendo una risoluzione spaziale di FWHM=0''.11 (39 pc). Per la stima del contributo stellare è stato interpolato il profilo di luce della galassia con una serie di gaussiane usando in combinazione l'immagine NIRI ad alta risoluzione e un'immagine ottenuta al TNG per coprire anche le parti esterne della galassia. La cinematica stellare è stata estratta dalle bande di assorbimento del CO a 2.29 micron. Sono stati adottati modelli di Jeans per interpolare la cinematica stellare e la distribuzione di brillanza superficiale per determinare i valori di anisotropia (beta) e MBH. La qualità dei dati spettroscopici non ha permesso di misurare una cinematica molto estesa, pertanto sono state fatte delle assunzioni su (M/L)_K e su beta. Il limite superiore della MBH risulta nell'intervallo tra 1x 10e9 Msun e 3.45 x 10e9 Msun a seconda dei valori che vengono assunti per (M/L)_K e beta. Sono state osservate con STIS, la Wide Field and Planetary Camera 2 (WFPC2), e la Advanced Camera for Surveys (ACS) montati su HST, tre galassie che per le loro grandi masse, luminosità e dispersioni di velocità sono degli ottimi candidati per ospitare dei SMBH eccezionalmente massivi: Abell 1836-BCG, Abell 2052-BCG, Abell 3565-BCG (Capitolo 6). I dati hanno fornito dettagli sulla struttura e sul profilo di massa della componente stellare, sulla profondita' ottica della polvere e sulle distribuzioni spaziale e cinematica del gas ionizzato entro le regioni più centrali delle galassie. Sono stati costruiti modelli dinamici, che tengono conto del profilo di massa osservato e includono il contributo del SMBH, per riprodurre la cinematica ottenuta dallo studio della riga di emissione di [NII]. La cinematica e la morfologia regolari di Abell 1836-BCG e Abell~3565-BCG, hanno permesso di ottenere rispettivamente MBH = 3.61 (+0.41,-0.50) x 10e9 Msun e 1.34 (+021,-0.19) x 10e9 Msun. La mancanza di moti ordinati in Abell 2052-BCG, invece, ha impedito un accurato modello dinamico. E' stato cosi stimato un limite superiore della MBH < 4.60 x 10e9 Msun. Queste misure rappresentano un importante passo avanti verso la caratterizzazione della funzione di massa dei SMBH, suggerendo un andamento più ripido della MBH-sigma nella regione ad alte sigma a causa o di una più grande dispersione della relazione o perché la legge MBH-sigma risulta diversa. Infine, è stata stimata la massa del SMBH di NGC 4278 (Capitolo 7) utilizzando il teorema del viriale e misurando le componenti larghe delle righe di emissione osservate nello spettro STIS. Si è assunto che il gas fosse uniformemente distribuito in una sfera di un certo raggio. A seconda delle dimensioni adottate per la regione in cui si formano le righe larghe, la massa va da 7 x 10e7 and 2 x 10e9 Msun, in accordo con i limiti superiori trovati seguendo altre assunzioni sulla distribuzione del gas. Il nucleo di NGC 4278 è una sorgente ultravioletta molto variabile. L'ampiezza e il tempo scala di questa variazione sono analoghi a quelli trovati per le galassie con una debole attività nucleare. Questa variabilità in ultravioletto è tipica dei nuclei galattici attivi a bassa luminosità. Le conclusioni di questa tesi possono essere riassunte in tre punti: 1) con le MBH ottenute attraverso modelli semplici siamo riusciti a mappare la relazione MBH-sigma per un campione molto ampio e vario di galassie che comprende tutta la popolazione locale dei SMBH. Queste stime risultano consistenti con la relazione MBH-sigma, senza mostrare dipendenze dovute alla distanza delle galassie, al loro tipo morfologico e alla presenza di barre. Queste stime di MBH possono essere usate per studiare l'andamento e la dispersione delle altre relazioni di scala dei SMBH. 2) Usando i risultati di questo lavoro è stato studiato il legame tra la MBH, lo sferoide e l'intera galassia (compreso l'alone di materia oscura). E' stato confermato che MBH risulta strettamente connesso con sigma indipendentemente dal tipo morfologico, e che il piano fondamentale dei buchi neri è principalmente legato da questa proprietà. 3) E' stata caratterizzata la parte alta della funzione di massa dei SMBH dell'universo locale per capire il legame tra l'evoluzione dei SMBH e la formazione gerarchica delle galassie. Questo è stato fatto misurando MBH in una galassia ellittica molto massiccia NGC~1265 usando dati della cinematica stellare ottenuti con ottica adattiva e in tre galassie molto brillanti attraverso la cinematica del gas derivata da dati di HST. Queste misure suggeriscono un andamento piu' ripido della MBH-sigma in nella regione ad alte sigma, dovuta o a una più grande dispersione della relazione o a una legge diversa che predice una crescita più veloce dei SMBH rispetto a sigma.

In this thesis, we focus on the structural components observed in the central regions of disk galaxies, namely bulges and bars. We aim to better understand the formation and evolution scenarios which could lead to the bulges and bars observed in the nearby universe. This study was performed from an observational point of view, by analyzing either the structural and photometric properties of bulges and bars, their kinematics, and stellar population characteristics.

Many clusters of galaxies contain large quantities of hot diffuse gas. I have studied the properties of waves in this gas using Lagrangian perturbations. The gas is far more thermally stable than is commonly thought. For bremsstrahlung cooling, all modes that remain oscillatory are damped. Galaxy motions, especially the oscillations of a central cD galaxy, are an important way of generating large amplitude waves in cluster gas. This is especially pertinent in view of the growing realization that cD galaxies are not at rest with respect to the cluster. I also present evidence that weak magnetic fields tangled on scales of ~ 10 kpc are common in cluster gas. Electrons responsible for the flow of heat in the gas must travel along the field lines, leading to a global reduction in heat flux. The superposition of many different field lines implies that the cluster gas is a multiphase medium. Such a picture has been suggested independently by the claimed observation of mass drop-out from cooling flows. I also show some results from a more advanced study using real magnetic fields rather than random walk models.

In this thesis I investigate the dynamics and stellar populations of a sample of 28 edge-on early-type (S0--Sb) disk galaxies, 22 of which host a boxy or peanut-shaped bulge. I begin by constructing mass models of the galaxies based on their observed photometry and stellar kinematics. Subject to cosmologically motivated assumptions about the shape of dark haloes, I measure in a purely dynamical way their stellar and dark masses. I make a preliminary comparison between the dynamically determined stellar masses and those predicted by stellar population models. I then compare the Tully-Fisher (luminosity--velocity) relations of the spirals and S0s in the sample. I show that S0s are systematically fainter at a given rotational velocity, but the amount by which they are fainter is less than expected by models in which they are the products of truncation of star formation in spirals. This raises the possibility that S0s are smaller or more concentrated than spirals of the same mass. I then study the vertical structure of the boxy and peanut-shaped bulges of a subset of the sample. Among this sample of five galaxies, I find one example in which the stellar populations show no evidence that the bulge and the disk formed in different processes, and in which the bulge is in perfectly cylindrical rotation, i.e. its line-of-sight velocity does not change with height above the disk. This galaxy is probably a pure disk galaxy. However, even with this small sample, I also show that cylindrical rotation and homogeneous stellar populations are not ubiquitous properties of boxy and peanut-shaped bulges. Finally I analyse central and radial trends in the stellar populations of the bulges of full sample of 28 galaxies. I find that, at a given velocity dispersion, the central stellar populations of these barred early-type disk galaxies are identical to those of elliptical galaxies, which suggests that secular evolution does not dominate the centre of these galaxies. However, the radial metallicity gradients are shallower than those of ellipticals. This is qualitatively consistent with chemodynamical models of bar formation, in which radial inflow and outflow smears out pre-existing gradients.

Numerical methods of resonant dynamics with applications to the Galaxy are considered in this thesis. We derive generating functions for first-order perturbation theory and the associated orbital frequencies by matrix calculus. For two action-angle spaces (J,θ) and (i,φ) related by a canonical map I·φ+s, we show that J can be averaged over ergodic orbits φ to provide an estimator of I to within O(|s|²). We provide examples in one and two dimensions and compare the technique to calculations of actions by numerical line integration in Poincaré sections. We then use spectral dynamics and the Laskar frequency map (Laskar, 1993) to identify the dynamically important resonances of the 'flattened' axisymmetric isochrone potential. We simulate resonant capture in a low-order resonance by populating representative tori of a spherical isochrone Hamiltonian and integrating the orbits while adiabatically introducing axisymmetry. We use the averaging technique described above to observe the fraction of orbits captured, and we compare the result to a theoretical prediction. We return to first-order perturbation theory to analyse its strengths and weaknesses, in particular near orbital pericentre, and when one action is significantly smaller than another. We also reproduce the expected pendulum dynamics in the resonant action-angle plane for orbits in our capture simulation. We develop the concept of adaptive dynamics: we vary the initial orbital energy of the particles in the capture simulations and show that resonant and non-resonant orbits can be identified as clusters in the perturbed action plane. For a given Hamiltonian, we use the perturbed frequencies and a linear regression fit in the action plane as diagnostics of a set of model Hamiltonians on a grid in a suitable parameter space. We find we are able to constrain the parameters of a model Hamiltonian by this method. Finally, we reject the null hypothesis that resonant structures in phase space can be found by traditional methods of density estimation.

Thèse de doctorat : Astrophysique : Strasbourg 1 : 2008. Thèse de doctorat : Astrophysics : Universiteit van Amsterdam, Nederland : 2008.<br>Thèse soutenue sur un ensemble de travaux. Thèse soutenue en co-tutelle. Titre provenant de l'écran-titre. Notes bibliogr.

This thesis is a theoretical study of supermassive black holes (SMBHs) in merging galaxies. We consider the dynamics that govern inspiralling SMBH pairs and gravitational-wave (GW) recoiling SMBHs, as well as the fueling of active galactic nuclei (AGN) during galaxy mergers. In particular, we focus on the observable signatures that could distinguish dual or recoiling AGN from those in isolated galaxies, and we explore the implications of these events for the coordinated evolution of SMBHs and galaxies. In the second and third chapters, semi-analytical models for GW-recoiling SMBHs are developed. The second chapter illustrates that bound recoiling SMBHs may have long wandering timescales and that recoil events can self-regulate SMBH growth. In the third chapter, we study the evolution of recoiling SMBHs in evolving, gaseous merger remnants. We find that the presence of gas greatly influences recoiling SMBH trajectories and may partially suppress even large recoil kicks in some cases. We also show that kinematically- and spatially-offset AGN can have substantial lifetimes for a wide range in kick speeds. Finally, this chapter illustrates that GW recoil influences the observed SMBH-galaxy relations as well as central star formation in the merger remnant. In the fourth chapter we turn our attention to inspiralling SMBH pairs with kiloparsec-scale separations. We use a novel approach to model the narrow-line emission from these SMBH pairs, in order to understand their relationship to observations of double-peaked narrow-line AGN. Our results indicate that double-peaked narrow-line AGN often arise from gas kinematics rather than from dual SMBH motion, but that the latter are a generic, short-lived phase of SMBH inspiral in gaseous mergers. We identify several diagnostics that could aid in distinguishing the true AGN pairs in the double-peaked sample. Finally, the fifth chapter examines a particular galaxy that exhibits signatures of both a recoiling AGN and an AGN pair. Applying methods developed throughout this thesis, we design models for both scenarios that are well-matched to the available data. Currently, neither possibility can be excluded for this object, but our models constrain the most relevant parameters for etermining its nature and for the design of future observations.<br>Astronomy

L’observation d’un phénomène physique s’appuie en général sur l’évolution d’une observable en fonction du temps. Une telle série temporelle contient les informations de base sur l’état du système étudié. Dans cette thèse, nous exploitons ce concept afin d’explorer l’évolution dynamique complexe qui peut avoir lieu dans les systèmes autogravitants Hamiltoniens. Nous traitons les coordonnées dans l’espace des phases des corps célestes comme des signaux, que nous analysons par la suite en utilisant différentes méthodes de traitement du signal, plus particulièrement la fonction d’autocorrélation et la transformée d’ondelettes. Dans notre analyse nous considérons tour à tour la dynamique à grande échelle des galaxies et celle, interne, des amas stellaires denses<br>The monitoring of physical phenomena (often) rests on a mapping of an observable as a function of time. Such time series encode basic information about the state of the system under study. In this thesis, we build on this concept to explore the intricate evolution of gravitational Hamiltonian systems. We treat the phase-space coordinates of celestial bodies as signals which we then analyze using processing techniques, such as autocorrelation identification and wavelet transforms. We consider in turn the large-scale dynamics of galaxies, and the internal dynamics of dense stellar clusters. [. . . ]

We combine precision radial velocity data from four different published works of the stars in the Leo II dwarf spheroidal galaxy. This yields a data set that spans 19 years, has 14 different epochs of observation, and contains 372 unique red giant branch stars, 196 of which have repeat observations. Using this multi-epoch data set, we constrain the binary fraction for Leo II. We generate a suite of Monte Carlo simulations that test different binary fractions using Bayesian analysis and determine that the binary fraction for Leo II ranges from 0.30(-0.10)(+0.09) to 0.34(-0.11)(+0.11), depending on the distributions of binary orbital parameters assumed. This value is smaller than what has been found for the solar neighborhood (similar to 0.4-0.6) but falls within the wide range of values that have been inferred for other dwarf spheroidals (0.14-0.69). The distribution of orbital periods has the greatest impact on the binary fraction results. If the fraction we find in Leo II is present in low-mass ultra-faints, it can artificially inflate the velocity dispersion of those systems and cause them to appear more dark matter rich than in actuality. For a galaxy with an intrinsic dispersion of 1 km s(-1) and an observational sample of 100 stars, the dispersion can be increased by a factor of 1.5-2 for Leo II-like binary fractions or by a factor of three. for binary fractions on the higher end of what has been seen in other dwarf spheroidals.

Cette thèse aborde des questions et présente de résultats qui exigent la combinaison des deux disciplines: d’une part, nous souhaitons comprendre et développer des outils fondamentaux des systèmes hamiltoniens et d’autre part nous envisageons de les utiliser pour étudier la dynamique de certains modèles de galaxies barrées. Pour cette raison, nous allons commencer par étudier d’importants phénomènes dynamiques concernant la stabilité des oscillations périodiques dans les systèmes hamiltoniens à N degrés de liberté ainsi que les applications N–symplectiques couplées. Ensuite, nous allons étendre notre travail au voisinage de ces régions et analyser les orbites quasipériodiques pour trouver des conditions dans lesquelles ces phénomènes disparaissent et pour lesquelles le comportement devient chaotique. Ceci sera effectué, en calculant les indices de GALI le long de chaque orbite de référence. Si l’orbite est périodique stable, la méthode GALI peut être utilisée pour déterminer la dimensionnalité du tore autour de cette orbite dans l’espace des phases à 2N–dimensions. Cette méthode peut alors être appliqué pour détecter les régimes où ces tores n’existent plus et où la plupart des choix de conditions initiales conduisent à des orbites chaotiques. Nous étudierons donc un système de N– applications standard couplées et en cherchant des orbites périodiques stables limitées par le tore au–delà duquel le chaos apparait. Afin d’ atteindre cet objectif, nous choisissons deux types de conditions initiales : a) localisées dans l’ espace réel, en excitant un “petit” nombre de particules (appelé “breathers”) et en étudiant leur mouvement régulier ou chaotique et b) localisées dans l’espace de Fourier (appelé q–“breather”), en excitant maintenant un “petit” nombre de modes normaux et en étudiant les phénomènes récurrents. Nous passons ensuite au second thème principal de cette thèse en étudiant en détails un problème fondamental de dynamique astrophysique : les orbites d’étoiles dans le potentiel galactique. A partir de modèles qui décrivent des galaxies et leur mouvement d’étoiles, il est bien - connu que l’ analyse des orbites périodiques et leur stabilité, peut fournir des informations très utiles sur l’évolution des galaxies. Les orbites périodiques stable sont associées à un mouvement régulier, puisqu’ils sont entourés d’un tore quasi–périodique. Une question fondamentale qui se pose alors est l’étendue de ces régions de stabilité. Un autre résultat en dynamique galactique est la présence de plusieurs orbites chaotiques comportant des caractéristiques de galaxies, comme la rotation de barre. Le phénomène de “stickiness”(orbites “collantes”) est également très fréquent dans ce genre de systèmes Hamiltoniens, c’ est-à-dire que leurs orbites révèlent leur nature chaotiques lentement. Plusieurs nouvelles méthodes de détection du chaos ont été introduites et appliquées au cours des dernières années pour la détection de mouvement chaotique ou régulier dans des modèles de galaxies, soit en étudiant la comportement des vecteurs déviation ou par l’analyse de séries chronologiques construites par les coordonnées de chaque orbite. Dans cette thèse, nous nous consacrons au modèle de galaxies barrée de Ferrers et nous étudions non seulement la distinction entre les solutions régulières, “sticky” ou chaotiques, mais aussi l’ importance de ces conclusions sur un intervalle de temps ayant un sens physique, c’est-à-dire environ un temps de Hubble. Pour accomplir cela, nous utiliserons la méthode de “Generalized Alignment Indexes” (GALI) pour la distinction entre mouvement chaotique ou régulier ainsi que de nouvelles manières d’ interprétation des spectres de Fourier et de la distribution de vitesse ou de quantit´e de mouvement. La combinaison de tout cela nous permet d’atteindre deux objectifs : Tout d’abord, nous pouvons détecter rapidement et efficacement la véritable nature des orbites et d’autre part, nous pouvons distinguer entre orbites chaotiques de diffusion orbitale dans l’espace réel différente. Nous avons montré qu’ il existe des orbites chaotiques se comportant de manière “régulière” suffisamment longtemps pour que leur caractéristiques n’aient pas encore été révélées du point de vue observationnel. Nous donnons enfin quelques résultats sur des orbites régulières concernant leur complexité orbitale, en terme de dimension du tore<br>This thesis addresses questions and presents results that require the combination of two disciplines : on the one hand, we wish to develop and understand fundamental tools of Hamiltonian systems and, on the other hand, we plan to use them to study the dynamics of certain basic models of barred galaxies. For this reason we shall start by investigating some important dynamical phenomena concerning the stability of periodic oscillations in N degree of freedom Hamiltonian systems and N coupled symplectic maps. Furthermore, we will extend our study to the vicinity of such motions and analyze quasiperiodic orbits aiming to find conditions under which they break down and chaotic behavior settles in. This will be accomplished by computing the GALI indices along every reference orbit. If the central periodic orbit is stable, the GALI method can be used to determine the dimensionality of the tori surrounding this orbit in the 2N–dimensional phase space. Furthermore, it can be applied to detect regimes where such tori cease to exist and most choices of initial conditions lead to chaotic orbits. We shall do this by studying a system of N coupled standard maps, searching for stable periodic motion surrounded by of tori beyond which there is chaos. In order to achieve this goal, we choose two different types of initial conditions: a) localized in real space, exciting a “small” number of particles (called a breather) and studying their regular or chaotic motion and b) localized in Fourier space (called q–breather), exciting a “small” number of normal modes and studying recurrence phenomena. We then turn to the detailed study of orbital star motion in galactic potentials which constitutes a fundamental aspect of dynamical astronomy and is the second major theme of this thesis. Starting with models that describe galaxies and their star motion, it is well–known that the analysis of periodic orbits, and their stability, can provide very useful information about galaxy evolution. Stable periodic orbits are associated with regular motion, since they are surrounded by quasi– periodic tori. A fundamental question that arises therefore is what is the extent of these stability regions? Another recent result in galactic dynamics is that there are also several chaotic orbits that can support galaxy features, like rotating bars. The phenomenon of “stickiness” (“sticky” orbits) is also very common in this kind of Hamiltonian systems, i. E. Orbits that their chaotic nature takes a long time to be revealed. Several new chaos detection methods have been introduced and applied in the last years for the detection of chaotic and regular motion in galaxy models, either by studying the behavior of deviation vectors or by analyzing time series constructed by the coordinates of each orbit. In this thesis, we shall focus on a Ferrers’ barred galaxy model and study not only the distinction between regular, sticky and chaotic solutions but also the significance of these findings over time interval that have a physical meaning, i. E. Roughly a Hubble time. To accomplish this we will use the method Generalized Alignment Indexes (GALI) for the distinction between the chaotic and regular motion as well as new ways of interpreting Fourier spectra and momentum distribution. Combining all these we achieve two goals: First, we are able to detect fast and efficiently the true nature of the orbits and second, we can distinguish between chaotic orbits with different types of orbital diffusion in real space. We find that there are chaotic orbits that behave in a “regular–like” manner for long enough times that their characteristics are not yet revealed from an observational point of view. Finally, we present some results concerning several regular orbits with regard to their orbital complexity, in terms of torus dimensionality

We study the large-scale dynamics of the interstellar medium in barred galaxies. The interest in doing this is two-fold. On the one hand, the hydrodynamic flow is the source of many interesting physical phenomena, such as shocks and spiral arms. On the other hand, it is a powerful tool to constrain the characteristics of individual galaxies. Approximately half of this thesis is devoted to understanding the general characteristics of the gas dynamics. There are two key ingredients. The first is ballistic closed orbits. We investigate the connection between closed orbits and the full hydrodynamic flow. We show how they also form the basis to explain bar-driven spiral arms. The second key ingredient is shocks. These can arise at the transition between different families of closed orbits, or when the spiral arms become too strong. Under certain conditions, shocks become hydrodynamically unstable and produce density fluctuations that may have an observational counterpart in the form of asymmetries in the Milky Way molecular gas distribution. We also explore systematically how the gas flow is affected by a change in the parameters that characterise the bar, such as its length, strength and pattern speed. Through the study of the gas dynamics, inferences can be made about the structure of galaxies. We have compared our models with observations of the Milky Way. First, we revisit and refine the Binney et al (1991) model, one of the most successful models for the gas flow in the Galaxy. Then, we present new models that while preserving the good properties of the previous model can also correct its main shortcomings. These models can qualitatively account for most of the observational signatures of the Galactic bar and allow us to constrain its characteristics, such as its pattern speed, length and strength. However, we show that is difficult to find a model that accounts for all the important observational features simultaneously due to the high dimensionality of parameter space involved. We argue that automatic fitting method are necessary. To this end, we develop a new quantitative method to fit Milky Way longitude-velocity diagrams that is based on feature matching.

We present deep optical images of the Large and Small Magellanic Clouds (LMC and SMC) using a low cost telephoto lens with a wide field of view to explore stellar substructure in the outskirts of the stellar disk of the LMC (< 10 degrees from the LMC center). These data have higher resolution than existing star count maps, and highlight the existence of stellar arcs and multiple spiral arms in the northern periphery, with no comparable counterparts in the south. We compare these data to detailed simulations of the LMC disk outskirts, following interactions with its low mass companion, the SMC. We consider interaction in isolation and with the inclusion of the Milky Way tidal field. The simulations are used to assess the origin of the northern structures, including also the low density stellar arc recently identified in the Dark Energy Survey data by Mackey et al. at similar to 15 degrees. We conclude that repeated close interactions with the SMC are primarily responsible for the asymmetric stellar structures seen in the periphery of the LMC. The orientation and density of these arcs can be used to constrain the LMC's interaction history with and impact parameter of the SMC. More generally, we find that such asymmetric structures should be ubiquitous about pairs of dwarfs and can persist for 1-2 Gyr even after the secondary merges entirely with the primary. As such, the lack of a companion around a Magellanic Irregular does not disprove the hypothesis that their asymmetric structures are driven by dwarf-dwarf interactions.

We present VIMOS-Very Large Telescope (VLT) spectroscopy of the Frontier Fields cluster MACS. J0416.1-2403 (z = 0.397). Taken as part of the CLASH-VLT survey, the large spectroscopic campaign provided more than 4000 reliable redshifts over similar to 600 arcmin(2), including similar to 800 cluster member galaxies. The unprecedented sample of cluster members at this redshift allows us to perform a highly detailed dynamical and structural analysis of the cluster out to similar to 2.2 r(200) (similar to 4Mpc). Our analysis of substructures reveals a complex system composed of a main massive cluster (M-200 similar to 0.9 x 10(15) M-circle dot and sigma(V r200) similar to 1000 km s(-1)) presenting two major features: (i) a bimodal velocity distribution, showing two central peaks separated by Delta V-rf similar to 1100 km s(-1) with comparable galaxy content and velocity dispersion, and (ii) a projected elongation of the main substructures along the NE-SW direction, with a prominent sub-clump similar to 600 kpc SW of the center and an isolated BCG approximately halfway between the center and the SW clump. We also detect a low-mass structure at z similar to 0.390, similar to 10' south of the cluster center, projected at similar to 3Mpc, with a relative line-of-sight velocity of Delta V-rf similar to 1700 km s(-1). The cluster mass profile that we obtain through our dynamical analysis deviates significantly from the "universal" NFW, being best fit by a Softened Isothermal Sphere model instead. The mass profile measured from the galaxy dynamics is found to be in relatively good agreement with those obtained from strong and weak lensing, as well as with that from the X-rays, despite the clearly unrelaxed nature of the cluster. Our results reveal an overall complex dynamical state of this massive cluster and support the hypothesis that the two main subclusters are being observed in a pre-collisional phase, in agreement with recent findings from radio and deep X-ray data. In this article, we also release the entire redshift catalog of 4386 sources in the field of this cluster, which includes 60 identified Chandra X-ray sources and 105 JVLA radio sources.

We present multisightline absorption spectroscopy of cool gas around three lensing galaxies at z = 0.4-0.7. These lenses have half-light radii r(e) = 2.6-8 kpc and stellar masses of log M-*/M-circle dot = 10.9-11.4, and therefore resemble nearby passive elliptical galaxies. The lensed QSO sightlines presented here occur at projected distances of d = 3-15 kpc (or d approximate to 1-2 r(e)) from the lensing galaxies, providing for the first time an opportunity to probe both interstellar gas at r similar to r(e) and circumgalactic gas at larger radii r >> r(e) of these distant quiescent galaxies. We observe distinct gas absorption properties among different lenses and among sightlines of individual lenses. Specifically, while the quadruple lens for HE 0435-1223 shows no absorption features to very sensitive limits along all four sightlines, strong MgII, Fe II, Mg I, and Ca II absorption transitions are detected along both sightlines near the double lens for HE 0047-1756, and in one of the two sightlines near the double lens for HE 1104-1805. The absorbers are resolved into 8-15 individual components with a line-of-sight velocity spread of Delta v approximate to 300-600 km s(-1). The large ionic column densities, log N greater than or similar to 14, observed in two components suggest that these may be Lyman limit or damped Ly a absorbers with a significant neutral hydrogen fraction. The majority of the absorbing components exhibit a uniform supersolar Fe/Mg ratio with a scatter of < 0.1 dex across the full Delta v range. Given a predominantly old stellar population in these lensing galaxies, we argue that the observed large velocity width and Fe-rich abundance pattern can be explained by SNe Ia enriched gas at radius r similar to r(e). We show that additional spatial constraints in line-of-sight velocity and relative abundance ratios afforded by a multisightline approach provide a powerful tool to resolve the origin of chemically enriched cool gas in massive haloes.