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Journal articles on the topic 'Model quasar'

Author: Grafiati

Published: 28 May 2022

Last updated: 30 July 2025

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1

Oogi, Taira, Motohiro Enoki, Tomoaki Ishiyama, Masakazu A. R. Kobayashi, Ryu Makiya, and Masahiro Nagashima. "The quasar clustering and its evolution in a semi-analytic model based on ultra high-resolution N-body simulations." Proceedings of the International Astronomical Union 11, S319 (2015): 61. http://dx.doi.org/10.1017/s1743921315010881.

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AbstractWe investigate clustering properties of quasars using a new version of our semi-analytic model of galaxy and quasar formation with state-of-the-art cosmological N-body simulations (Ishiyama et al. 2015; Oogi et al. 2015). We assume that a major merger of galaxies triggers quasar activity. We find that the quasar bias does not depend significantly on the quasar luminosity, similar to observed trends. This result reflects the fact that quasars with a fixed luminosity have various Eddington ratios and thus have various host halo masses that primarily determine the quasar bias. The quasar

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Li, Xiaolei, Ryan E. Keeley, Arman Shafieloo, et al. "Hubble diagram at higher redshifts: model independent calibration of quasars." Monthly Notices of the Royal Astronomical Society 507, no. 1 (2021): 919–26. http://dx.doi.org/10.1093/mnras/stab2154.

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ABSTRACT In this paper, we present a model-independent approach to calibrate the largest quasar sample. Calibrating quasar samples is essentially constraining the parameters of the linear relation between the log of the ultraviolet (UV) and X-ray luminosities. This calibration allows quasars to be used as standardized candles. There is a strong correlation between the parameters characterizing the quasar luminosity relation and the cosmological distances inferred from using quasars as standardized candles. We break this degeneracy by using Gaussian process regression to model-independently rec

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Cai, Zhenyi. "The Composite Spectral Energy Distribution of Quasars Is Surprisingly Universal Since Cosmic Noon." Universe 10, no. 11 (2024): 431. http://dx.doi.org/10.3390/universe10110431.

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Leveraging the photometric data of the Sloan Digital Sky Survey and the Galaxy Evolution Explorer (GALEX), we construct mean/median spectral energy distributions (SEDs) for unique bright quasars in redshift bins of 0.2 and up to z≃3, after taking the GALEX non-detection into account. Further correcting for the absorption of the intergalactic medium, these mean/median quasar SEDs constitute a surprisingly redshift-independent mean/median composite SED from the rest-frame optical down to ≃500 A˚ for quasars with bolometric luminosity brighter than 1045.5ergs−1. Moreover, the mean/median composit

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Fu, Yuming, Xue-Bing Wu, Yifan Li, et al. "CatNorth: An Improved Gaia DR3 Quasar Candidate Catalog with Pan-STARRS1 and CatWISE." Astrophysical Journal Supplement Series 271, no. 2 (2024): 54. http://dx.doi.org/10.3847/1538-4365/ad2ae6.

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Abstract A complete and pure sample of quasars with accurate redshifts is crucial for quasar studies and cosmology. In this paper, we present CatNorth, an improved Gaia Data Release 3 (Gaia DR3) quasar candidate catalog with more than 1.5 million sources in the 3π sky built with data from Gaia, Pan-STARRS1, and CatWISE2020. The XGBoost algorithm is used to reclassify the original Gaia DR3 quasar candidates as stars, galaxies, and quasars. To construct training/validation data sets for the classification, we carefully built two different master stellar samples in addition to the spectroscopic g

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Yue, Minghao, Xiaohui Fan, Jinyi Yang, and Feige Wang. "A Mock Catalog of Gravitationally-lensed Quasars for the LSST Survey." Astronomical Journal 163, no. 3 (2022): 139. http://dx.doi.org/10.3847/1538-3881/ac4cb0.

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Abstract We present a mock catalog of gravitationally-lensed quasars at z qso < 7.5 with simulated images for the Rubin Observatory Legacy Survey of Space and Time (LSST). We adopt recent measurements of quasar-luminosity functions to model the quasar population, and use the CosmoDC2 mock galaxy catalog to model the deflector galaxies, which successfully reproduces the observed galaxy-velocity dispersion functions up to z d ∼ 1.5. The mock catalog is highly complete for lensed quasars with Einstein radius θ E > 0.″07 and quasar absolute magnitude M i < − 20. We estimate that there are

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Macfarlane, C., P. N. Best, J. Sabater, et al. "The radio loudness of SDSS quasars from the LOFAR Two-metre Sky Survey: ubiquitous jet activity and constraints on star formation." Monthly Notices of the Royal Astronomical Society 506, no. 4 (2021): 5888–907. http://dx.doi.org/10.1093/mnras/stab1998.

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ABSTRACT We examine the distribution of radio emission from ∼42 000 quasars from the Sloan Digital Sky Survey, as measured in the LOFAR Two-metre Sky Survey (LoTSS). We present a model of the radio luminosity distribution of the quasars that assumes that every quasar displays a superposition of two sources of radio emission: active galactic nuclei (jets) and star formation. Our two-component model provides an excellent match to the observed radio flux density distributions across a wide range of redshifts and quasar optical luminosities; this suggests that the jet-launching mechanism operates

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Eilers, Anna–Christina, David W. Hogg, Bernhard Schölkopf, Daniel Foreman-Mackey, Frederick B. Davies, and Jan–Torge Schindler. "A Generative Model for Quasar Spectra." Astrophysical Journal 938, no. 1 (2022): 17. http://dx.doi.org/10.3847/1538-4357/ac8ead.

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Abstract We build a multi-output generative model for quasar spectra and the properties of their black hole engines, based on a Gaussian process latent-variable model. This model treats every quasar as a vector of latent properties such that the spectrum and all physical properties of the quasar are associated with non-linear functions of those latent parameters; the Gaussian process kernel functions define priors on the function space. Our generative model is trained with a justifiable likelihood function that allows us to treat heteroscedastic noise and missing data correctly, which is cruci

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Li, Xiaolei, Ryan E. Keeley, and Arman Shafieloo. "Redshift Evolution of the X-Ray and Ultraviolet Luminosity Relation of Quasars: Calibrated Results from SNe Ia." Astrophysical Journal 983, no. 2 (2025): 141. https://doi.org/10.3847/1538-4357/adc2fe.

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Abstract Quasars could serve as standard candles if the relation between their ultraviolet (UV) and X-ray luminosities can be accurately calibrated. Previously, we developed a model-independent method to calibrate quasar standard candles using the distance–redshift relation reconstructed from Type Ia supernovae (SNe Ia) at z < 2 using Gaussian process regression. Interestingly, we found that the calibrated quasar standard candle data set preferred a deviation from ΛCDM at redshifts above z > 2. One possible interpretation of these findings is that the calibration parameters of the quasar

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Solomon, R., and D. Stojkovic. "Variability in quasar light curves: using quasars as standard candles." Journal of Cosmology and Astroparticle Physics 2022, no. 04 (2022): 060. http://dx.doi.org/10.1088/1475-7516/2022/04/060.

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Abstract A relation between the variational slope, sF , and the mean absolute magnitude, 〈M〉, in the light curves of 58 spectroscopically confirmed quasars is measured with a dispersion of 0.15dex. Assuming it holds for quasars in general, not only does this relation add to our working knowledge of quasar variability but it also shows great promise at accurately measuring luminosity distance to a quasar in a model independent way. An accurate, model independent measure of the luminosity distance would allow quasars to be added to the cosmic distance ladder, easily extending the ladder out far

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Jin, Xin, Yanxia Zhang, Jingyi Zhang, Yongheng Zhao, Xue-bing Wu, and Dongwei Fan. "Efficient selection of quasar candidates based on optical and infrared photometric data using machine learning." Monthly Notices of the Royal Astronomical Society 485, no. 4 (2019): 4539–49. http://dx.doi.org/10.1093/mnras/stz680.

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ABSTRACT We aim to select quasar candidates based on the two large survey databases, Pan-STARRS and AllWISE. Exploring the distribution of quasars and stars in the colour spaces, we find that the combination of infrared and optical photometry is more conducive to select quasar candidates. Two new colour criterions (yW1W2 and iW1zW2) are constructed to distinguish quasars from stars efficiently. With iW1zW2, 98.30 per cent of star contamination is eliminated, while 99.50 per cent of quasars are retained, at least to the magnitude limit of our training set of stars. Based on the optical and infr

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Schindler, Jan-Torge, Eduardo Bañados, Thomas Connor, et al. "The Pan-STARRS1 z > 5.6 Quasar Survey. III. The z ≈ 6 Quasar Luminosity Function." Astrophysical Journal 943, no. 1 (2023): 67. http://dx.doi.org/10.3847/1538-4357/aca7ca.

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Abstract We present the z ≈ 6 type-1 quasar luminosity function (QLF), based on the Pan-STARRS1 (PS1) quasar survey. The PS1 sample includes 125 quasars at z ≈ 5.7–6.2, with −28 ≲ M 1450 ≲ −25. With the addition of 48 fainter quasars from the SHELLQs survey, we evaluate the z ≈ 6 QLF over −28 ≲ M 1450 ≲ −22. Adopting a double power law with an exponential evolution of the quasar density (Φ(z) ∝ 10 k(z−6); k = −0.7), we use a maximum likelihood method to model our data. We find a break magnitude of M * = − 26.38 − 0.60 + 0.79 mag , a faint-end slope of α = − 1.70 − 0.19 + 0.29 , and a steep bri

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Masci, F. J., and R. L. Webster. "Dust Obscuration in the Universe." Publications of the Astronomical Society of Australia 12, no. 2 (1995): 146–52. http://dx.doi.org/10.1017/s132335800002018x.

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AbstractA substantial population of red quasars has been discovered in a complete sample of flat-spectrum radio sources. Dust is the most likely cause of the reddening in this sample. The location of the dust is poorly known, but may either be in the line-of-sight to the quasar, or in the immediate quasar environment. In this paper we are interested in models where the dust is located in the line of sight to the quasar. We calculate the probability distribution of the optical depth in galactic dust as a function of source redshift, using a range of parameters which might describe real galaxies

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Nair, A., and M. Vivek. "Fraction of broad absorption line quasars in different radio morphologies." Monthly Notices of the Royal Astronomical Society 511, no. 4 (2022): 4946–62. http://dx.doi.org/10.1093/mnras/stac204.

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ABSTRACT In this study, we investigated the orientation model of Broad Absorption Line (BAL) quasars using a sample of sources that are common in Sloan Digital Sky Survey (SDSS) Data Release (DR)-16 quasar catalogue and Very Large Array (VLA)-Faint Images of the Radio Sky at Twenty Centimeters (FIRST) survey. Using the radio cut-out images from the FIRST survey, we first designed a deep-learning model using convolutional neural networks (CNN) to classify the quasar radio morphologies into the core-only, young jet, single lobe, or triples. These radio morphologies are further sub-classified int

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Brodzeller, Allyson, and Kyle Dawson. "Modeling the Spectral Diversity of Quasars in the Sixteenth Data Release from the Sloan Digital Sky Survey." Astronomical Journal 163, no. 3 (2022): 110. http://dx.doi.org/10.3847/1538-3881/ac4600.

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Abstract We present a new approach to capturing the broad diversity of emission-line and continuum properties in quasar spectra. We identify populations of spectrally similar quasars through pixel-level clustering on 12,968 high signal-to-noise ratio (S/N) spectra from the Sloan Digital Sky Survey (SDSS) in the redshift range of 1.57 < z < 2.4. Our clustering analysis finds 396 quasar spectra that are not assigned to any population, 15 misclassified spectra, and 6 quasars with incorrect redshifts. We compress the quasar populations into a library of 684 high-S/N composite spectra, anchor

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Ďurovčíková, Dominika, Harley Katz, Sarah E. I. Bosman, Frederick B. Davies, Julien Devriendt, and Adrianne Slyz. "Reionization history constraints from neural network based predictions of high-redshift quasar continua." Monthly Notices of the Royal Astronomical Society 493, no. 3 (2020): 4256–75. http://dx.doi.org/10.1093/mnras/staa505.

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ABSTRACT Observations of the early Universe suggest that reionization was complete by z ∼ 6, however, the exact history of this process is still unknown. One method for measuring the evolution of the neutral fraction throughout this epoch is via observing the Lyα damping wings of high-redshift quasars. In order to constrain the neutral fraction from quasar observations, one needs an accurate model of the quasar spectrum around Lyα, after the spectrum has been processed by its host galaxy but before it is altered by absorption and damping in the intervening intergalactic medium (IGM). In this p

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Kapahtia, Akanksha, and T. Roy Choudhury. "Simulating the epoch of helium reionization in photon-conserving semi-numerical code SCRIPT." Journal of Cosmology and Astroparticle Physics 2024, no. 05 (2024): 093. http://dx.doi.org/10.1088/1475-7516/2024/05/093.

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Abstract The reionization of the second electron of helium (HeII) leaves important imprints on the thermal and ionization state of the intergalactic medium (IGM). Observational evidence suggests that HeII reionization ended at z ≃ 3 due to ionizing photons emitted predominantly by quasars. We present efficient semi-numerical simulations of helium reionization in a 230 h-1 Mpc box, that takes into account the spatial patchiness of reionization coupled with photoheating of the IGM. Dark matter haloes are assigned quasars using empirical measurements of the quasar luminosity function, assuming a

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Chen, Jie, Linhua Jiang, Shengxiu Sun, Zijian Zhang, and Mouyuan Sun. "Estimating Bolometric Luminosities of Type 1 Quasars with Self-organizing Maps." Astrophysical Journal 988, no. 2 (2025): 204. https://doi.org/10.3847/1538-4357/ade307.

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Abstract We present a new method to calculate bolometric luminosities for unobscured, type 1 quasars with multiband photometric data. Bolometric luminosity is a fundamental property for understanding quasars, and it is commonly estimated from monochromatic luminosities using bolometric corrections that often neglect quasar spectral energy distribution (SED) diversity. We take advantage of the fact that most quasars now have multiband observations from UV to mid-IR and construct SEDs for a well-defined sample of Sloan Digital Sky Survey (SDSS) quasars at 0.5 ≤ z ≤ 2. Based on this fiducial samp

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Sharma, Yash M., Frederick B. Davies, Prakash Gaikwad, Fahad Nasir та Sarah E. I. Bosman. "Behavior of the Lyα Damping Wings as a Function of Reionization Topology". Astrophysical Journal 983, № 2 (2025): 118. https://doi.org/10.3847/1538-4357/adbe6d.

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Abstract The damping wing signatures in high-redshift quasars have proven instrumental in studying the epoch of reionization. With the upcoming Euclid mission set to discover many more quasars, it is crucial to explore what this new set of quasars might reveal not only about the reionization history, but also about its topology. The topology should influence the shape and variation of quasar-damping wing signals across sightlines. We use 21cmFAST to generate patchy reionization models in cosmological volumes with diverse astrophysical parameters for the ionizing sources. We examine the median

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Smirnov, A. I. "A quasar model." Russian Physics Journal 48, no. 10 (2005): 1101–2. http://dx.doi.org/10.1007/s11182-006-0031-y.

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Ren, Keven, and Michele Trenti. "A Physical Model for the Quasar Luminosity Function Evolution between Cosmic Dawn and High Noon." Astrophysical Journal 923, no. 1 (2021): 110. http://dx.doi.org/10.3847/1538-4357/ac2e02.

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Abstract Modeling the evolution of the number density distribution of quasars through the quasar luminosity function (QLF) is critical to improving our understanding of the connection between black holes, galaxies, and their halos. Here we present a novel semiempirical model for the evolution of the QLF that is fully defined after the specification of a free parameter, the internal duty cycle, ε DC, along with minimal other assumptions. All remaining model parameters are fixed upon calibration against the QLF at two redshifts, z = 4 and z = 5. Our modeling shows that the evolution at the brigh

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Cloonan, Aidan P., Gourav Khullar, Kate A. Napier, et al. "COOL-LAMPS. VIII. Known Wide-separation Lensed Quasars and Their Host Galaxies Reveal a Lack of Evolution in M _BH/M _⋆ Since z ∼ 3." Astrophysical Journal 987, no. 2 (2025): 194. https://doi.org/10.3847/1538-4357/addabf.

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Abstract Wide-separation lensed quasars (WSLQs) are a rare class of strongly lensed quasars, magnified by foreground massive galaxy clusters, with typically large magnifications of the multiple quasar images. They are a relatively unexplored opportunity for detailed study of quasar host galaxies. The current small sample of known WSLQs has a median redshift of z ≈ 2.1, larger than most other samples of quasar host galaxies studied to date. Here, we derive precise constraints on the properties of six WSLQs and their host galaxies, using parametric surface brightness fitting, measurements of qua

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Niu, Qi, Yichao Li, Yidong Xu, Hong Guo, and Xin Zhang. "Prospects for Observing High-redshift Radio-loud Quasars in the SKA Era: Paving the Way for 21 cm Forest Observations." Astrophysical Journal 978, no. 2 (2025): 145. https://doi.org/10.3847/1538-4357/ad9b97.

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Abstract The 21 cm forest is a sensitive probe for the early heating process and small-scale structures during the epoch of reionization (EOR), to be realized with the upcoming Square Kilometre Array (SKA). Its detection relies on the availability of radio-bright background sources, among which the radio-loud quasars are very promising, but their abundance during the EOR is still poorly constrained due to limited observations. In this work, we use a physics-driven model to forecast future radio-loud quasar observations. We fit the parameters of the model using observational data of high-redshi

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Mishra, Sapna, M. Vivek, Hum Chand, and Ravi Joshi. "Appearance versus disappearance of broad absorption line troughs in quasars." Monthly Notices of the Royal Astronomical Society 504, no. 3 (2021): 3187–202. http://dx.doi.org/10.1093/mnras/stab782.

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ABSTRACT We present a new set of 84 broad absorption line (BAL) quasars (1.7 &lt; zem &lt; 4.4) exhibiting an appearance of C iv BAL troughs over 0.3–4.8 rest-frame years by comparing the Sloan Digital Sky Survey Data Release (SDSSDR)-7, SDSSDR-12, and SDSSDR-14 quasar catalogues. We contrast the nature of BAL variability in this appearing BAL quasar sample with a disappearing BAL quasar sample studied in the literature by comparing the quasar’s intrinsic, BAL trough, and continuum parameters between the two samples. We find that appearing BAL quasars have relatively higher redshift an

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Sun 孙, Zechang 泽昌, Yuan-Sen 源森 Ting 丁, and Zheng 峥. Cai 蔡. "Quasar Factor Analysis—An Unsupervised and Probabilistic Quasar Continuum Prediction Algorithm with Latent Factor Analysis." Astrophysical Journal Supplement Series 269, no. 1 (2023): 4. http://dx.doi.org/10.3847/1538-4365/acf2f1.

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Abstract Since their first discovery, quasars have been essential probes of the distant Universe. However, due to our limited knowledge of its nature, predicting the intrinsic quasar continua has bottlenecked their usage. Existing methods of quasar continuum recovery often rely on a limited number of high-quality quasar spectra, which might not capture the full diversity of the quasar population. In this study, we propose an unsupervised probabilistic model, quasar factor analysis (QFA), which combines factor analysis with physical priors of the intergalactic medium to overcome these limitatio

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Pipien, S., J. G. Cuby, S. Basa, et al. "High-redshift quasar selection from the CFHQSIR survey." Astronomy & Astrophysics 617 (September 2018): A127. http://dx.doi.org/10.1051/0004-6361/201833488.

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Being observed only one billion years after the Big Bang, z ∼ 7 quasars are a unique opportunity for exploring the early Universe. However, only two z ∼ 7 quasars have been discovered in near-infrared surveys: the quasars ULAS J1120+0641 and ULAS J1342+0928 at z = 7.09 and z = 7.54, respectively. The rarity of these distant objects, combined with the difficulty of distinguishing them from the much more numerous population of Galactic low-mass stars, requires using efficient selection procedures. The Canada-France High-z Quasar Survey in the Near Infrared (CFHQSIR) has been carried out to searc

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Khrykin, Ilya S., Joseph F. Hennawi, Gábor Worseck, and Frederick B. Davies. "The first measurement of the quasar lifetime distribution." Monthly Notices of the Royal Astronomical Society 505, no. 1 (2021): 649–62. http://dx.doi.org/10.1093/mnras/stab1288.

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ABSTRACT Understanding the growth of the supermassive black holes (SMBH) powering luminous quasars, their co-evolution with host galaxies, and impact on the surrounding intergalactic medium (IGM) depends sensitively on the duration of quasar accretion episodes. Unfortunately, this time-scale, known as the quasar lifetime, tQ, is still uncertain by orders of magnitude ($t_{\rm Q} \simeq 0.01\, {\rm Myr} - 1\, {\rm Gyr}$). However, the extent of the He ii Ly α proximity zones in the absorption spectra of zqso ∼ 3–4 quasars constitutes a unique probe, providing sensitivity to lifetimes up to ∼30

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Kembhavi, Ajit, and A. C. Fabian. "The Soft X-ray Excess in Quasars and Deep X-ray Surveys." Symposium - International Astronomical Union 159 (1994): 217–20. http://dx.doi.org/10.1017/s0074180900175060.

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We examine the surface density of quasars expected in the ROSAT PSPC surveys, using quasar optical luminosity functions and model continuum spectra including a soft X-ray excess. We show that the surface density is a sensitive function of the characteristic energy of the soft excess, and the absorption within the quasar as well as the interstellar medium. Comparision of the predicted surface density with the results of various surveys allows useful constraints to be put on the nature of the soft excess.

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Wang, Xilin. "Direct observation evidence for the origin of broad emission lines in quasars: Understanding emission via absorption." Theoretical and Natural Science 26, no. 1 (2023): 261–72. http://dx.doi.org/10.54254/2753-8818/26/20241105.

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This year marks the 60^th anniversary of quasar discovery in 1963. The kinematics of gaseous clouds in quasars have been the subject of decades-long debate, focusing on two modelsrotation and blowing-wind. The rotation model, wherein gaseous clouds orbit black holes, is widely accepted by astronomers and frequently used to measure supermassive black hole (SMBH) masses in quasars. Another model is blowing-wind model, in which the gaseous clouds are outflows and in linear motion toward all directions. Our study creatively employs the quasar absorption line technique, utilizing atomic hydrogen Ba

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Storey-Fisher, Kate, David W. Hogg, Hans-Walter Rix, et al. "Quaia, the Gaia-unWISE Quasar Catalog: An All-sky Spectroscopic Quasar Sample." Astrophysical Journal 964, no. 1 (2024): 69. http://dx.doi.org/10.3847/1538-4357/ad1328.

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Abstract We present a new, all-sky quasar catalog, Quaia, that samples the largest comoving volume of any existing spectroscopic quasar sample. The catalog draws on the 6,649,162 quasar candidates identified by the Gaia mission that have redshift estimates from the space observatory’s low-resolution blue photometer/red photometer spectra. This initial sample is highly homogeneous and complete, but has low purity, and 18% of even the bright (G < 20.0) confirmed quasars have discrepant redshift estimates (∣Δz/(1 + z)∣ > 0.2) compared to those from the Sloan Digital Sky Survey (SDSS). In th

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Zhang, X. G. "SDSS J1451 + 2709 a normal blue quasar but mis-classified as a H ii galaxy in the BPT diagram by flux ratios of narrow emission lines." Monthly Notices of the Royal Astronomical Society 509, no. 3 (2021): 4626–36. http://dx.doi.org/10.1093/mnras/stab3322.

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ABSTRACT In the manuscript, we discuss properties of SDSS J1451 + 2709, a normal blue quasar but mis-classified as a H ii galaxy in the BPT diagram (called as a mis-classified quasar). The emission lines around H α and around H β are well measured by different model functions with broad Balmer lines described by Gaussian or Lorentz functions, in the SDSS spectrum in 2007 and in the KPNO spectrum in 1990. After considering variations of broad emission lines, different model functions lead to different determined fluxes of narrow emission lines, but the different narrow emission line flux ratios

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Lerner, Eric J. "Magnetic self-compression in laboratory plasmas, quasars and radio galaxies. Part I." Laser and Particle Beams 4, no. 2 (1986): 193–213. http://dx.doi.org/10.1017/s0263034600001750.

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A model of quasars and their associated jets as phenomena of magnetic selfcompression is presented. Magnetic field self-compression, as observed in laboratory plasma focus devices, results in increases in energy density of more than 108 and in even larger increases in transferred power density. Our model, based on the scaling of these phenomena to astrophysical dimensions, avoids the problems of gravitationallyconfined approaches. It presents a mechanism by which the energy of a quasar is immediately derived from a volume nearly 106 times larger than the observed quasar radiating volume and is

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Eftekharzadeh, S., A. D. Myers, and E. Kourkchi. "A Halo Occupation Interpretation of Quasars at z ∼ 1.5 Using Very Small-Scale Clustering Information." Monthly Notices of the Royal Astronomical Society 486, no. 1 (2019): 274–82. http://dx.doi.org/10.1093/mnras/stz770.

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Abstract We combine the most precise small-scale ($\lt 100\, \rm h^{-1}kpc$) quasar clustering constraints to date with recent measurements at large scales ($\gt 1\, \rm h^{-1}Mpc$) from the extended Baryon Oscillation Spectroscopic Survey (eBOSS) to better constrain the satellite fraction of quasars at z ∼ 1.5 in the halo occupation formalism. We build our Halo Occupation Distribution (HOD) framework based on commonly used analytic forms for the one and two-halo terms with two free parameters: the minimum halo mass that hosts a central quasar and the fraction of satellite quasars that are wit

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Qi, Yan-Qing, Tong Liu, Zhen-Yi Cai, and Mouyuan Sun. "Nucleosynthesis Contribution of Neutrino-dominated Accretion Flows to the Chemical Evolution of Active Galactic Nuclei." Astrophysical Journal 934, no. 1 (2022): 1. http://dx.doi.org/10.3847/1538-4357/ac7a43.

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Abstract Recent observations of quasars show high line-flux ratios in their broad emission lines and the ratios appear to be independent of redshift up to z ≳ 6, which indicates that the broad-line regions of these early quasars are surprisingly metal-rich. Here, we revisit the chemical evolution of high-redshift quasars by adding a new ingredient, i.e., the neutrino-dominated accretion flows (NDAFs) with outflows, on top of the conventional core-collapse supernovae (CCSNe). In the presence of the chemical contribution from NDAFs with outflows, the total metal mass (i.e., the summation of the

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Hawkins, M. R. S. "Quasar Variability: New Surveys and New Models." International Astronomical Union Colloquium 184 (2002): 351–56. http://dx.doi.org/10.1017/s0252921100031006.

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AbstractIn this paper results from a monitoring programme of a large sample of quasars comprising regular yearly observations over a period of 23 years are presented. Structure functions of the light curves are calculated and compared with predictions for models of quasar variability of current interest. These include recently published models of varibility from accretion disk instability, variability from starbursts or supernovae, and variations caused by the microlensing effect of compact bodies along the line of sight. The analysis favours the accretion disk model for low luminosity AGN, bu

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Klindt, L., D. M. Alexander, D. J. Rosario, E. Lusso, and S. Fotopoulou. "Fundamental differences in the radio properties of red and blue quasars: evolution strongly favoured over orientation." Monthly Notices of the Royal Astronomical Society 488, no. 3 (2019): 3109–28. http://dx.doi.org/10.1093/mnras/stz1771.

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Abstract A minority of the optically selected quasar population are red at optical wavelengths due to the presence of dust along the line of sight. A key focus of many red quasar studies is to understand their relationship with the overall quasar population: are they blue quasars observed at a (slight) inclination angle or do they represent a transitional phase in the evolution of quasars? Identifying fundamental differences between red and blue quasars is key to discriminate between these two paradigms. To robustly explore this, we have uniformly selected quasars from the Sloan Digital Sky Su

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Yang, Jinyi, Xiaohui Fan, Feige Wang, et al. "Deep XMM-Newton Observations of an X-ray Weak Broad Absorption Line Quasar at z = 6.5." Astrophysical Journal Letters 924, no. 2 (2022): L25. http://dx.doi.org/10.3847/2041-8213/ac45f2.

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Abstract We report X-ray observations of the most distant known gravitationally lensed quasar, J0439+1634 at z = 6.52, which is also a broad absorption line (BAL) quasar, using the XMM-Newton Observatory. With a 130 ks exposure, the quasar is significantly detected as a point source at the optical position with a total of 358 − 19 + 19 net counts using the EPIC instrument. By fitting a power law plus Galactic absorption model to the observed spectra, we obtain a spectral slope of Γ = 1.45 − 0.09 + 0.10 . The derived optical-to-X-ray spectral slope α ox is − 2.07 − 0.01 + 0.01 , suggesting that

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Secrest, Nathan J., Sebastian von Hausegger, Mohamed Rameez, Roya Mohayaee, and Subir Sarkar. "A Challenge to the Standard Cosmological Model." Astrophysical Journal Letters 937, no. 2 (2022): L31. http://dx.doi.org/10.3847/2041-8213/ac88c0.

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Abstract We present the first joint analysis of catalogs of radio galaxies and quasars to determine whether their sky distribution is consistent with the standard ΛCDM model of cosmology. This model is based on the cosmological principle, which asserts that the universe is statistically isotropic and homogeneous on large scales, so the observed dipole anisotropy in the cosmic microwave background (CMB) must be attributed to our local peculiar motion. We test the null hypothesis that there is a dipole anisotropy in the sky distribution of radio galaxies and quasars consistent with the motion in

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Worseck, Gábor, Ilya S. Khrykin, Joseph F. Hennawi, J. Xavier Prochaska, and Emanuele Paolo Farina. "Dating individual quasars with the He ii proximity effect." Monthly Notices of the Royal Astronomical Society 505, no. 4 (2021): 5084–103. http://dx.doi.org/10.1093/mnras/stab1685.

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ABSTRACT Constraints on the time-scales of quasar activity are key to understanding the formation and growth of supermassive black holes (SMBHs), quasar triggering mechanisms, and possible feedback effects on their host galaxies. However, observational estimates of this so-called quasar lifetime are highly uncertain (tQ ∼ 104–109 yr), because most methods are indirect and involve many model-dependent assumptions. Direct evidence of earlier activity is gained from the higher ionization state of the intergalactic medium (IGM) in the quasar environs, observable as enhanced Ly α transmission in th

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ZHU, ZONG-HONG, and XIANG-PING WU. "SAMPLE INCOMPLETENESS IN THE STUDY OF THE QUASAR-GALAXY ASSOCIATIONS AS A RESULT OF GRAVITATIONAL LENSING." International Journal of Modern Physics D 07, no. 03 (1998): 463–69. http://dx.doi.org/10.1142/s0218271898000309.

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For decades, the angular associations between faint galaxies and high redshift quasars have remained to be a well-known puzzle, which is often cited as an evidence for the noncosmological origin of quasar redshifts. This happens because the attempt at interpreting the phenomenon as being due to gravitational lensing fails in producing the reported high amplitude of the quasar-galaxy associations unless some unconventional hypotheses are made such as an extremely large velocity dispersion for galaxies, a serious contamination of the overall quasar number counts or a strong matter clustering on

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Ma, F. "Hidden Blazars In Radio Loud Quasars?" Symposium - International Astronomical Union 195 (2000): 411–12. http://dx.doi.org/10.1017/s0074180900163326.

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We present the initial results from our search for hidden blazars via CIV emission line variability among radio loud quasars. The implications on models of quasar Broad Emission Line Regions are discussed, and we focus on the tidally disrupted star model.

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Akiba, Tatsuya, Jason Dexter, W. N. Brandt, et al. "Reprocessing Models for the Optical Light Curves of Hypervariable Quasars from the Sloan Digital Sky Survey Reverberation Mapping Project." Astrophysical Journal 953, no. 2 (2023): 124. http://dx.doi.org/10.3847/1538-4357/ace1e1.

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Abstract We explore reprocessing models for a sample of 17 hypervariable quasars, taken from the Sloan Digital Sky Survey Reverberation Mapping project, which all show coordinated optical luminosity hypervariability with amplitudes of factors ≳2 between 2014 and 2020. We develop and apply reprocessing models for quasar light curves in simple geometries that are likely to be representative of quasar inner environments. In addition to the commonly investigated thin-disk model, we include the thick-disk and hemisphere geometries. The thick-disk geometry could, for instance, represent a magnetical

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Zakamska, Nadia L., Ai-Lei Sun, Michael A. Strauss, et al. "Host galaxies of high-redshift extremely red and obscured quasars." Monthly Notices of the Royal Astronomical Society 489, no. 1 (2019): 497–516. http://dx.doi.org/10.1093/mnras/stz2071.

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Abstract We present Hubble Space Telescope 1.4–1.6 $\mu$m images of the hosts of 10 extremely red quasars (ERQs) and six type 2 quasar candidates at z = 2–3. ERQs, whose bolometric luminosities range between 1047 and 1048 erg s−1, show spectroscopic signs of powerful ionized winds, whereas type 2 quasar candidates are less luminous and show only mild outflows. After performing careful subtraction of the quasar light, we clearly detect almost all host galaxies. The median rest-frame B-band luminosity of the ERQ hosts in our sample is $10^{11.2}\, \mathrm{L}_{\odot }$, or ∼4L* at this redshift.

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Minev, Milen, Trifon Trifonov, Valentin D. Ivanov, et al. "Results of a long-term optical variability study of 11 quasars and VRI photometry of comparison stars." Monthly Notices of the Royal Astronomical Society 531, no. 4 (2024): 4746–61. http://dx.doi.org/10.1093/mnras/stae1479.

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ABSTRACT We present the results of a 15-yr long-term optical monitoring of 11 quasars conducted with the 2-m Ritchey–Chretien–Coude and the 50/70 cm Schmidt telescopes at the Rozhen National Astronomical Observatory, Bulgaria. Our observations are performed with standard Johnson-Cousins $VRI$ band filters and for each quasar we present a set of comparison standard stars that can be used for monitoring of objects in these fields (including finding charts for the stars identification). The variability and periodicity of each quasar are analysed individually and discussed. The physical properties

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Pang, Sen, Hoiio Kong, Zijun Li, Weibo Kao, and Yanxia Zhang. "Deep-Learning-Based Identification of Broad-Absorption Line Quasars." Applied Sciences 15, no. 3 (2025): 1024. https://doi.org/10.3390/app15031024.

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The accurate classification of broad-absorption line (BAL) quasars and non-broad-absorption line (non-BAL) quasars is key in understanding active galactic nuclei (AGN) and the evolution of the universe. With the rapid accumulation of data from large-scale spectroscopic survey projects (e.g., LAMOST, SDSS, and DESI), traditional manual classification methods face limitations. In this study, we propose a new method based on deep learning techniques to achieve an accurate distinction between BAL quasars and non-BAL quasars. We use a convolutional neural network (CNN) as the core model, in combina

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Ye 叶, Guangping 广平, Huanian 华年 Zhang 张, and Qingwen 庆文 Wu 吴. "Machine Learning–based Search of High-redshift Quasars." Astrophysical Journal Supplement Series 275, no. 1 (2024): 19. http://dx.doi.org/10.3847/1538-4365/ad79ee.

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Abstract We present a machine learning search for high-redshift (5.0 < z < 6.5) quasars using the combined photometric data from the Dark Energy Spectroscopic Instrument (DESI) Imaging Legacy Surveys and the Wide-field Infrared Survey Explorer survey. We explore the imputation of missing values for high-redshift quasars, discuss the feature selections, compare different machine learning algorithms, and investigate the selections of class ensemble for the training sample, then we find that the random forest model is very effective in separating the high-redshift quasars from various conta

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Hamolli, Lindita, Mimoza Hafizi, Francesco De Paolis, and Esmeralda Guliqani. "Investigating Gravitationally Lensed Quasars Observable by Nancy Grace Roman Space Telescope." Galaxies 11, no. 3 (2023): 71. http://dx.doi.org/10.3390/galaxies11030071.

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In this work, we investigate the possibility of observing quasars, particularly lensed quasars, by the Nancy Grace Roman Space Telescope (Roman). To this aim, based on the capabilities of the Roman Space Telescope and the results from the quasar luminosity function (QLF) in the infrared band of the Spitzer Space Telescope imaging survey, we calculated the number of quasars expected to be in its field of view. In order to estimate the number of lensed quasars, we develop a Monte Carlo simulation to estimate the probability that a quasar is lensed once or more times by foreground galaxies. Using

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Davies, Frederick B., Joseph F. Hennawi, and Anna-Christina Eilers. "Time-dependent behaviour of quasar proximity zones at z ∼ 6." Monthly Notices of the Royal Astronomical Society 493, no. 1 (2019): 1330–43. http://dx.doi.org/10.1093/mnras/stz3303.

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ABSTRACT Since the discovery of z ∼ 6 quasars two decades ago, studies of their Ly α-transparent proximity zones have largely focused on their utility as a probe of cosmic reionization. But even when in a highly ionized intergalactic medium, these zones provide a rich laboratory for determining the time-scales that govern quasar activity and the concomitant growth of their supermassive black holes. In this work, we use a suite of 1D radiative transfer simulations of quasar proximity zones to explore their time-dependent behaviour for activity time-scales from ∼103 to 108 yr. The sizes of the s

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Lian, Yujie, Shuo Cao, Marek Biesiada, Yun Chen, Yilong Zhang, and Wuzheng Guo. "Probing modified gravity theories with multiple measurements of high-redshift quasars." Monthly Notices of the Royal Astronomical Society 505, no. 2 (2021): 2111–23. http://dx.doi.org/10.1093/mnras/stab1373.

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ABSTRACT In this paper, we quantify the ability of multiple measurements of high-redshift quasars to constrain several theories of modified gravity, including the Dvali–Gabadadze–Porrati braneworld scenario, generalized Chaplygin gas, f(T) modified gravity, and modified polytropic Cardassian model. Recently released sample of 1598 quasars with X-ray and ultraviolet flux measurements in the redshift range of 0.036 ≤ z ≤ 5.1003, as well as a compilation of 120 intermediate-luminosity radio quasars covering the redshift of 0.46 &lt; z &lt; 2.76 are respectively used as standard probes at

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Schmidt, Kasper B., Hans-Walter Rix, Sebastian Jester, Phil Marshall, Gregory Dobler, and Joseph F. Hennawi. "Detecting Quasars by Their Variability." Proceedings of the International Astronomical Union 5, S267 (2009): 265. http://dx.doi.org/10.1017/s1743921310006423.

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We demonstrate that quantifying the intrinsic variability of quasars by fitting individual structure function data pairs with a 2-parameter power law model separates quasars from contaminating variable and non-variable point sources with a completeness of 93% and a purity of 99%. This approach can be used to select quasar samples in surveys like that being performed by Pan-STARRS1, where the usual color selection of quasars is not possible due to a filter system that is too red.

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Garofalo, David, Damian J. Christian, and Andrew M. Jones. "The Sub-Eddington Boundary for the Quasar Mass–Luminosity Plane: A Theoretical Perspective." Universe 5, no. 6 (2019): 145. http://dx.doi.org/10.3390/universe5060145.

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By exploring more than sixty thousand quasars from the Sloan Digital Sky Survey Data Release 5, Steinhardt & Elvis discovered a sub-Eddington boundary and a redshift-dependent drop-off at higher black hole mass, possible clues to the growth history of massive black holes. Our contribution to this special issue of Universe amounts to an application of a model for black hole accretion and jet formation to these observations. For illustrative purposes, we include ~100,000 data points from the Sloan Digital Sky Survey Data Release 7 where the sub-Eddington boundary is also visible and propose

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