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1
Mishra, Sapna, M. Vivek, Hum Chand und Ravi Joshi. „Appearance versus disappearance of broad absorption line troughs in quasars“. Monthly Notices of the Royal Astronomical Society 504, Nr. 3 (01.04.2021): 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 < zem < 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 and smaller probed time-scales as compared to the disappearing BAL quasars. To mitigate the effect of any redshift bias, we created control samples of appearing and disappearing BAL quasars that have similar redshift distribution. We find that the appearing BAL quasars are relatively brighter and have shallower and wider BAL troughs compared to the disappearing BAL sample. The distribution of quasar continuum variability parameters between the two samples is clearly separated, with the appearance of the BAL troughs being accompanied by the dimming of the continuum and vice versa. Spectral index variations in the two samples also point to the anticorrelation between the BAL trough and continuum variations consistent with the ‘bluer when brighter’ trend in quasars. We show that the intrinsic dust model is less likely to be a favourable scenario in explaining BAL appearance/disappearance. Our analysis suggests that the extreme variations of BAL troughs like BAL appearance/disappearance are mainly driven by changes in the ionization conditions of the absorbing gas.
2
Chen, Zhi-Fu, Huan-Chang Qin, Jin-Ting Cai, Yu-Tao Zhou, Zhe-Geng Chen, Ting-Ting Pang, Zhi-Wen Wang und Kang-Fa Cheng. „The Study of the Circumgalactic Medium with Quasar Pairs“. Astrophysical Journal Supplement Series 265, Nr. 2 (29.03.2023): 46. http://dx.doi.org/10.3847/1538-4365/acbe01.
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Abstract We have collected 10,025 foreground–background quasar pairs with projected distances d p < 500 kpc from the large quasar catalog of the Sloan Digital Sky Survey DR16Q. We investigate the properties of the Mg ii absorption lines with W r > 0.15 Å around foreground quasars, including both the line of sight (LOS; of foreground quasars) and transverse (TRA; perpendicular to the LOS) absorptions. Both the equivalent width (the correlation coefficient ρ = −0.915 and the probability P < 10−4 of no correlation) and incident rate (ρ = −0.964 and P < 10−6) of TRA Mg ii absorption lines are obviously anticorrelated with projected distance. The incident rate of TRA Mg ii absorption lines is obviously (>4σ) greater than that of LOS Mg ii absorption lines at projected distances d p < 200 kpc, while the TRA and LOS Mg ii both have similar (<3σ) incident rates at scales d p > 200 kpc. The anisotropic radiation from quasars would be the most possible interpretation for the anisotropic absorption around quasars. This could also indicate that the quasar radiation is not obviously impacting the gas halos of quasars at scales d p > 200 kpc.
3
Harutyunian, Haik A. „Are There Quasars at Non-Cosmological Distances?“ Symposium - International Astronomical Union 194 (1999): 428–31. http://dx.doi.org/10.1017/s0074180900162485.
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In Dravskikh & Dravskikh (1996) the results of a statistical analysis of quasar luminosity as a function of redshift, if it is assumed to be cosmological, are given (see Fig.1). Three quasar samples were analyzed separately: •quasars with absorption lines;•quasars associated with galaxies or association-quasars not having absorption lines (from Burbidge et al. 1996);•other quasars not included in the first two groups.
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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, Nr. 1 (20.12.2023): 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 Balmer absorption lines for identification, especially during eclipses of inner emitting clouds. The ambiguous presence of hydrogen Balmer absorption lines hints at massive eclipse clouds near central black holes, but detection is hindered by obscuration from dusty tori outside the broad emission line-producing region. We conduct an intensive survey among million quasars in Sloan Digital Sky Survey (SDSS) and acquire a small sample of quasars with hydrogen Balmer absorptions on their spectra. Three quasars exhibit significant variabilities over a decade, contradicting the blowing-wind model, which predicts constant motion along the line of sight with no absorption variabilities. The discovery servers as the direct observation evidence for the rotation model of broad emission lines in quasars. Rotation velocities of eclipse clouds, consistent with expected velocities of emission line clouds, confirm homology between absorption and emission clouds.
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Peng, Xing-Long, Zhi-Fu Chen, Zhi-Cheng He, Ting-Ting Pang und Zhi-Wen Wang. „Comprehensive Connection among the Quasars with Different Types of Outflow Absorption Lines“. Astrophysical Journal 963, Nr. 1 (21.02.2024): 3. http://dx.doi.org/10.3847/1538-4357/ad1e5e.
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Abstract It is commonly accepted that outflows from the central regions of quasars play a substantial role in regulating the global properties of the host galaxy. These outflows are typically detected through blueshifted absorption lines. However, the question remains whether outflows observed with different absorption line types indeed reflect the same environmental or evolutionary stage of the host galaxy. In this study, we use the Sloan Digital Sky Survey quasar catalog and employ the flux ratio of [O II] and [Ne V] emission lines as indicators to compare star formation rates (SFRs) within host galaxies of quasars exhibiting various outflow absorption line types: low-ionization broad absorption line (LoBAL), low-ionization Mini-BAL (LoMini-BAL), low-ionization narrow absorption line (LoNAL), high-ionization broad absorption line (HiBAL), high-ionization Mini-BAL (HiMini-BAL), and high-ionization narrow absorption line (HiNAL). Our findings indicate that the SFR of LoMini-BAL quasars is comparable to that of LoNAL quasars, somewhat less than that of LoBAL quasars, but markedly greater than that of HiBAL quasars. Furthermore, the SFR of HiMini-BAL quasars mirrors that of HiNAL or Non-abs (no associated absorption lines) quasars, but is significantly higher than that of HiBAL quasars. If we consider that differing absorption line types are indicative of the quasar evolution stage, our results propose an inclusive evolution sequence: LoBALs evolve into LoMini-BALs/LoNALs, then progress to HiBALs, and ultimately morph into HiMini-BALs/HiNALs/Non-abs. Concomitantly, the SFR within the host galaxies of quasars appears to decline noticeably nearing the LoNAL phase’s end and rejuvenates before the HiMini-BAL phase.
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Misawa, Toru, Rikako Ishimoto, Satoshi Kobu, Nobunari Kashikawa, Katsuya Okoshi, Akatoki Noboriguchi, Malte Schramm und Qiang Liu. „Exploratory Study of the Transverse Proximity Effect around BAL Quasars“. Astrophysical Journal 933, Nr. 2 (01.07.2022): 239. http://dx.doi.org/10.3847/1538-4357/ac7715.
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Abstract We aim to determine why there exists anisotropic H i absorption around quasars; i.e., the environments around quasars are highly biased toward producing strong H i absorption in the transverse direction while there exists a significant deficit of H i absorption within a few megaparsecs of quasars along the line of sight. The most plausible explanation for this opposite trend is that the transverse direction is shielded from quasar UV radiation by dust torus. However, a critical weakness of this explanation is that we do not have any information on the inclination angle of our sightline relative to the torus. In this study, we examine environments of quasars with broad-absorption troughs in their spectra (i.e., BAL quasars) because it is widely believed that BAL troughs are observed if the central continuum is viewed from the side through their powerful outflows near the dust torus. With closely separated 12 projected quasar pairs at different redshifts with a separation angle of θ < 120″, we examine H i absorption at foreground BAL quasars in the spectra of background quasars. We confirm that there exists optically thick gas around two of 12 BAL quasars, and that the mean H i absorption strength is EWrest ∼ 1 Å. This is consistent with past results of studies of non-BAL quasars, although not statistically significant. The origins of optically thick H i absorbers around BAL and non-BAL quasars could be different since their column densities are different by ∼3 orders of magnitude. A larger sample is required to narrow down possible scenarios explaining the anisotropic H i absorption around quasars.
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Hennawi, Joe. „The Circumgalactic Medium of Quasars“. Proceedings of the International Astronomical Union 9, S304 (Oktober 2013): 355. http://dx.doi.org/10.1017/s174392131400430x.
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AbstractI will argue that observations of the diffuse gas in the outskirts of quasar host galaxies, or the so called circumgalactic medium, are essential for understanding how luminous quasars evolve in a cosmological context. Such observations also provide a fruitful comparison to theory, because hydrodynamics at moderate overdensities is much easier to simulate than the complicated processes which trigger quasar activity. A novel technique will be introduced, whereby a foreground quasar can be studied in absorption against a background quasar, resolving scales as small as 30 kpc. This experiment reveals a rich absorption spectrum which contains a wealth of information about the physical conditions of diffuse gas around quasars. Hydrodynamical simulations of the massive dark matter halos which host luminous quasars under predict the amount of cool gas observed in quasar environs by a large factor, challenging our understanding of how massive galaxies form. I will also discuss a very sensitive search for Ly-alpha emission from the same gas which we study in absorption.
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Aldcroft, T., J. Bechtold, P. Smith, C. Foltz und G. Schmidt. „Optical Polarization and Line Variability in Quasars with Associated Absorption“. International Astronomical Union Colloquium 163 (1997): 681–82. http://dx.doi.org/10.1017/s0252921100043396.
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AbstractThe physical origin of associated absorption lines (zabs ≈ zqso) which are observed in radio-loud quasar is generally not well understood. Two observable properties, line variability and quasar optical polarization, can serve to constrain the possibilities. To this end, we have obtained high-resolution spectra (1 Å) and broad-band optical polarizations for over 30 radio-loud quasars with known CIV associated absorption. The quasars are at redshifts between about 1 and 2, and were previously observed spectroscopically at similar resolution between 1985 – 1986 by Foltz et al (1987). The associated CIV absorption systems include a variety of velocity profiles from weak single lines to very complex multi-component systems to the BAL-like profile of PHL 1157+0128. In this poster we show the first strong evidence for line variability in z > 1 radio-loud quasars. We find that in general the variability is less than ~ 30%. The optical polarization of CIV absorbed quasars is consistent with all radio-loud quasars.
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Ennesser, Lauren, Paul Martini, Andreu Font-Ribera und Ignasi Pérez-Ràfols. „The impact and mitigation of broad-absorption-line quasars in Lyman α forest correlations“. Monthly Notices of the Royal Astronomical Society 511, Nr. 3 (03.02.2022): 3514–23. http://dx.doi.org/10.1093/mnras/stac301.
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ABSTRACT Correlations in and with the flux transmission of the Lyman α (Ly α) forest in the spectra of high-redshift quasars are powerful cosmological tools, yet these measurements can be compromised if the intrinsic quasar continuum is significantly uncertain. One particularly problematic case is broad-absorption-line (BAL) quasars, which exhibit blueshifted absorption associated with many spectral features that are consistent with outflows of up to ∼0.1c. As these absorption features can both fall in the forest region and be difficult to distinguish from Ly α absorption, cosmological analyses eliminate the ∼12–16 per cent of quasars that exhibit BALs. In this paper, we explore an alternate approach that includes BALs in the Ly α autocorrelation function, with the exception of the expected locations of the BAL absorption troughs. This procedure returns over 95 per cent of the path-length that is lost by the exclusion of BALs, as well as increasing the density of sightlines. We show that including BAL quasars reduces the fractional uncertainty in the covariance matrix and correlation function by 12 per cent and does not significantly change the shape of the correlation function relative to analyses that exclude BAL quasars. We also evaluate different definitions of BALs, masking strategies, and potential differences in the quasar continuum in the forest region for BALs with different amounts of absorption.
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Miller, Timothy R., Nahum Arav, Xinfeng Xu und Gerard A. Kriss. „The contribution of quasar absorption outflows to AGN feedback“. Monthly Notices of the Royal Astronomical Society 499, Nr. 1 (28.09.2020): 1522–29. http://dx.doi.org/10.1093/mnras/staa2981.
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ABSTRACT Determining the distance of quasar absorption outflows from the central source (R) and their kinetic luminosity ($\dot{E}_\mathrm{\scriptstyle k}$) is crucial for understanding their contribution to active galactic nucleus (AGN) feedback. Here, we summarize the results for a sample of nine luminous quasars that were observed with the Hubble Space Telescope. We find that the outflows in more than half of the objects are powerful enough to be the main agents for AGN feedback, and that most outflows are found at R > 100 pc. The sample is representative of the quasar absorption outflow population as a whole and is unbiased towards specific ranges of R and $\dot{E}_\mathrm{\scriptstyle k}$. Therefore, the analysis results can be extended to the majority of such objects, including broad absorption line quasars. We find that these results are consistent with those of another sample (seven quasars) that is also unbiased towards specific ranges of R and $\dot{E}_\mathrm{\scriptstyle k}$. Assuming that all quasars have absorption outflows, we conclude that most luminous quasars produce outflows that can contribute significantly to AGN feedback. We also discuss the criterion for whether an outflow is energetic enough to cause AGN feedback effects.
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Wethers, Clare, Nischal Acharya, Roberto De Propris, Jari Kotilainen, Malte Schramm und Andreas Schulze. „No evidence for quenching in quasars“. Proceedings of the International Astronomical Union 15, S359 (März 2020): 82–88. http://dx.doi.org/10.1017/s1743921320002264.
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AbstractThe role of quasar feedback in galaxy evolution remains poorly understood. Throughout this work, we explore the effects of negative feedback on star formation in quasar host galaxies, analysing two distinct populations of quasars. The first is a sample of high-redshift (z > 2) low-ionisation broad absorption line quasars (LoBALs) - a class of quasars hosting energetic mass outflows, in which we find evidence for prolific star formation (>750Mʘyr–1) exceeding that of non-BAL quasars at the same redshift. The second is a population of 207 low-redshift (z < 0.3) quasars, in which we find an enhancement in the SFRs of quasar hosts compared to the underlying galaxy population, with no quasars residing in quiescent hosts over the last 2Gyr. Overall, we find no evidence for galaxy-wide quenching in either population, rather we suggest that the dominant effect of quasar activity is to enhance star formation in the galaxy.
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Drinkwater, M. J., R. L. Webster, P. J. Francis, T. Wiklind und F. Combes. „Dust-reddened Quasars“. Publications of the Astronomical Society of Australia 13, Nr. 2 (Mai 1996): 183–84. http://dx.doi.org/10.1017/s1323358000020774.
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We have recently discovered evidence for a population of radio-loud quasars that is reddened by dust. The dust is either along the line of sight to the quasars or is associated with the quasars. In the latter case the dust may be in molecular clouds in the quasar’s host galaxy, or in a molecular torus around the nucleus. We are planning to use 3 mm observations to search for molecular absorption lines (CO and HCO+) associated with dust at the redshift of these quasars. If any absorption systems are detected we will be able to deduce detailed information about the physical state of the molecular gas, hopefully showing which of the proposed locations of the dust is most likely.
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Jin, Jun-Jie, Xue-Bing Wu, Yuming Fu, Su Yao, Yan-Li Ai, Xiao-Tong Feng, Zi-Qi He et al. „The Large Sky Area Multi-Object Fiber Spectroscopic Telescope (LAMOST) Quasar Survey: Quasar Properties from Data Releases 6 to 9“. Astrophysical Journal Supplement Series 265, Nr. 1 (01.03.2023): 25. http://dx.doi.org/10.3847/1538-4365/acaf89.
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Abstract We report the fourth installment in the series of the Large Sky Area Multi-Object Fiber Spectroscopic Telescope (LAMOST) quasar survey, which includes quasars observed between 2017 September and 2021 June. There are in total 13,066 quasars reliably identified, of which 6685 are newly discovered that are not reported in the Sloan Digital Sky Survey (SDSS) DR14 quasar catalog or Million Quasars catalog. Because LAMOST does not provide accurate absolute flux calibration, we recalibrate the spectra with the SDSS/Pan-STARRS1 multiband photometric data. The emission-line properties of Hα, Hβ, Mg ii, and C iv and the continuum luminosities are measured by fitting the recalibrated spectra. We also estimate the single-epoch virial black hole masses (M BH) using the derived emission-line and continuum parameters. This is the first time that the emission-line and continuum fluxes were estimated based on LAMOST recalibrated quasar spectra. The catalog and spectra for these quasars are available online. After the 9 yr LAMOST quasar survey, there are in total 56,175 identified quasars, of which 24,127 are newly discovered. The LAMOST quasar survey not only discovers a great number of new quasars but also provides a database for investigating the spectral variability of the quasars observed by both LAMOST and SDSS and finding rare quasars, including changing-look quasars and broad absorption line quasars.
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M, Vivek, Akhil Nair und Sapna Mishra. „AGN outflows and its variability“. Proceedings of the International Astronomical Union 19, S378 (Dezember 2023): 16–21. http://dx.doi.org/10.1017/s1743921323003484.
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AbstractThe radiative mode of AGN feedback, operated through outflows, plays an essential role in the evolution of galaxies. Quasar outflows are detected as blue-shifted broad absorption lines in the UV/optical spectra of quasars. Thanks to the Sloan digital sky survey, 100,000 broad absorption line quasars are available now for ensemble statistical studies. This rich dataset has also enabled us to identify some peculiar cases of these sources. By quantifying the BAL fraction in radio-loud BAL quasars, our studies demonstrate a clear trend of increasing BAL fraction as the viewing angle approaches an edge-on orientation, favoring the orientation model of BAL quasars. Also, by contrasting the properties of BAL quasars with appearing and disappearing BAL troughs, our analysis suggests that the extreme variations in BAL troughs are driven by ionization changes.
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Rankine, Amy L., Paul C. Hewett, Manda Banerji und Gordon T. Richards. „BAL and non-BAL quasars: continuum, emission, and absorption properties establish a common parent sample“. Monthly Notices of the Royal Astronomical Society 492, Nr. 3 (16.01.2020): 4553–75. http://dx.doi.org/10.1093/mnras/staa130.
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ABSTRACT Using a sample of ≃144 000 quasars from the Sloan Digital Sky Survey Data Release 14, we investigate the outflow properties, evident in both absorption and emission, of high-ionization broad absorption line (BAL) and non-BAL quasars with redshifts 1.6 ≲ $z$ ≤ 3.5 and luminosities 45.3 erg s−1 < log10(Lbol) < 48.2 erg s−1. Key to the investigation is a continuum and emission-line reconstruction scheme, based on mean-field independent component analysis, that allows the kinematic properties of the C iv λ1550 emission line to be compared directly for both non-BAL and BAL quasars. C iv emission blueshift and equivalent width (EW) measurements are thus available for both populations. Comparisons of the emission-line and BAL trough properties reveal strong systematic correlations between the emission and absorption properties. The dependence of quantitative outflow indicators on physical properties such as quasar luminosity and luminosity relative to Eddington luminosity is also shown to be essentially identical for the BAL and non-BAL populations. There is an absence of BALs in quasars with the hardest spectral energy distributions (SEDs), revealed by the presence of strong He ii λ1640 emission, large C iv λ1550 emission EW, and no measurable blueshift. In the remainder of the C iv emission blueshift versus EW space, BAL and non-BAL quasars are present at all locations; for every BAL quasar, it is possible to identify non-BAL quasars with the same emission-line outflow properties and SED hardness. The co-location of BAL and non-BAL quasars as a function of emission-line outflow and physical properties is the key result of our investigation, demonstrating that (high-ionization) BALs and non-BALs represent different views of the same underlying quasar population.
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Sorini, Daniele, Romeel Davé und Daniel Anglés-Alcázar. „simba: the average properties of the circumgalactic medium of 2 ≤ z ≤ 3 quasars are determined primarily by stellar feedback“. Monthly Notices of the Royal Astronomical Society 499, Nr. 2 (05.10.2020): 2760–84. http://dx.doi.org/10.1093/mnras/staa2937.
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ABSTRACT We use the simba cosmological hydrodynamic simulation suite to explore the impact of feedback on the circumgalactic medium (CGM) and intergalactic medium (IGM) around 2 ≤ z ≤ 3 quasars. We identify quasars in simba as the most rapidly accreting black holes, and show that they are well matched in bolometric luminosity and correlation strength to real quasars. We extract Lyα absorption in spectra passing at different transverse distances ($10 \, \mathrm{kpc} \lesssim b \lesssim 10 \, \rm Mpc$) around those quasars, and compare to observations of the mean Lyα absorption profile. The observations are well reproduced, except within $100 \, \, \rm kpc$ from the foreground quasar, where simba overproduces absorption; this could potentially be mitigated by including ionization from the quasar itself. By comparing runs with different feedback modules activated, we find that (mechanical) AGN feedback has little impact on the surrounding CGM even around these most highly luminous black holes, while stellar feedback has a significant impact. By further investigating thermodynamic and kinematic properties of CGM gas, we find that stellar feedback, and not AGN feedback, is the primary physical driver in determining the average properties of the CGM around z ∼ 2–3 quasars. We also compare our results with previous works, and find that simba predicts much more absorption within $100 \, \rm kpc$ than the nyx and illustris simulations, showing that the Lyα absorption profile can be a powerful constraint on simulations. Instruments such as VLT-MUSE and upcoming surveys (e.g. WEAVE and DESI) promise to further improve such constraints.
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Simon, Leah E., und Fred Hamann. „Tracing Metallicity in High Redshift Quasars“. Proceedings of the International Astronomical Union 5, S265 (August 2009): 183–84. http://dx.doi.org/10.1017/s1743921310000517.
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AbstractWe present two ongoing studies of gas phase abundances around high redshift quasars. First, we examine broad emission line (BEL) metallicities for 29 quasars with 2.3 < z < 4.6 and far-infrared (far-IR) luminosities (LFIR) from 1013.4 to ≤ 1012.2 L⊙, corresponding to star formation rates (SFRs) of 6740 to ≤ 1360 M⊙ yr−1. Quasar samples sorted by LFIR might represent an evolutionary sequence if SFRs in quasar hosts generally diminish across quasar lifetimes. We create three composite spectra from rest-frame ultra-violet Sloan Digital Sky Survey spectra with increasing far-IR luminosity. We measure the N V(λ1240)/C IV(λ1550) and Si IV(λ1397)+O IV](λ1402)/C IV(λ1550) emission line flux ratios for each composite and find uniformly high (~5-10 times solar) metallicities for the three composites, and no evidence for changes in metal enrichment with changes in ongoing SFR. Second, we present preliminary results from the largest ever survey of high resolution associated absorption line (AAL) region metallicities and physical properties in a sample of high redshift (z > 3) quasars. This includes five quasars with previously known AALs at z > 4 and two well measured z ~3 quasars with unusually rich absorption spectra. We determine well-constrained metallicities of about twice solar for five AAL systems. We find a range of lower limits for AAL metallicities in the z > 4 quasars from 1/100ths solar to 3 times solar. Overall, these results for typically super-solar gas-phase metallicities near quasars are consistent with evolutionary schemes where the major episodes of star formation in the host galaxies occur before the visibly luminous quasar phase. High SFRs (comparable to ULIRGs) in the host galaxies are not clearly linked to younger or chemically less mature quasar environments.
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He, X. T., M. G. Smith, R. D. Cannon, J. A. Peacock, J. B. Oke und C. D. Impey. „Quasars in the Virgo cluster region“. Symposium - International Astronomical Union 119 (1986): 501–2. http://dx.doi.org/10.1017/s0074180900153306.
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The region of the Virgo cluster is the subject of an intensive quasar search, since quasars mill provide valuable probes of absorption due to galaxy haloes or the intracluster medium. It is also interesting to test the quasar-galaxy association in such a region of the nearest major cluster of galaxies. More than 200 quasar candidates were found in the Virgo cluster region using both slitless technique and machine search, 32 of them have been confirmed as quasars.
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Bischetti, Manuela, Fabrizio Fiore, Chiara Feruglio, Valentina D’Odorico, Nahum Arav, Tiago Costa, Kastytis Zubovas et al. „The Fraction and Kinematics of Broad Absorption Line Quasars across Cosmic Time“. Astrophysical Journal 952, Nr. 1 (01.07.2023): 44. http://dx.doi.org/10.3847/1538-4357/accea4.
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Abstract Luminous quasars are powerful targets to investigate the role of feedback from supermassive black holes (BHs) in regulating the growth phases of BHs themselves and of their host galaxies, up to the highest redshifts. Here we investigate the cosmic evolution of the occurrence and kinematics of BH-driven outflows, as traced by broad absorption line (BAL) features, due to the C iv ionic transition. We exploit a sample of 1935 quasars at z = 2.1–6.6 with bolometric luminosity log(L bol/erg s−1) ≳ 46.5, drawn from the Sloan Digital Sky Survey and from the X-Shooter legacy survey of Quasars at the Reionization Epoch (XQR-30). We consider rest-frame optical bright quasars to minimize observational biases due to quasar selection criteria. We apply a homogeneous BAL-identification analysis, based on employing composite template spectra to estimate the quasar intrinsic emission. We find a BAL quasar fraction close to 20% at z ∼ 2–4, while it increases to almost 50% at z ∼ 6. The velocity and width of the BAL features also increase at z ≳ 4.5. We exclude the possibility that the redshift evolution of the BAL properties is due to differences in terms of quasar luminosity and accretion rate. These results suggest significant BH feedback occurring in the 1 Gyr old universe, likely affecting the growth of BHs and, possibly, of their host galaxies, as supported by models of early BH and galaxy evolution.
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Capellupo, Daniel M., Fred Hamann, Joseph C. Shields, Tom A. Barlow und Paola Rodriguez. „Variability in Quasar Broad Absorption Line Outflows“. Proceedings of the International Astronomical Union 5, S267 (August 2009): 394. http://dx.doi.org/10.1017/s1743921310006782.
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Broad absorption lines (BALs) in quasar spectra identify high-velocity outflows that likely exist in all quasars and could play a major role in feedback to galaxy evolution (e.g., Di Matteo et al. 2005). Studying the variability in these BALs can help us understand the structure, evolution, and basic physical properties of these outflows. We are investigating BAL variability in a sample of 25 luminous quasars at 1.2 < z < 2.9 with multi-epoch observations that cover time scales from less than around a month to 7.7 years in the quasar rest-frame. We investigate changes in the C iv λ1549 BALs, and we see a variety of phenomena, including some BALs that either appeared or disappeared completely and other BALs that did not change at all over the whole observation period.
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Nair, A., und M. Vivek. „Fraction of broad absorption line quasars in different radio morphologies“. Monthly Notices of the Royal Astronomical Society 511, Nr. 4 (27.01.2022): 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 into core-dominated and lobe-dominated sources. The CNN models can classify the sources with a high precision of >98 ${{\ \rm per\ cent}}$ for all the morphological sub-classes. The average BAL fraction in the resolved core, core-dominated, and lobe-dominated quasars are consistent with the BAL fraction inferred from radio and infrared surveys. We also present the distribution of BAL quasars as a function of quasar orientation by using the radio core-dominance as an orientation indicator. A similar analysis is performed for HiBALs, LoBALs, and FeLoBALs. All the radio morphological sub-classes and BAL sub-classes show an increase in BAL fraction at high orientation angles of the jets with respect to the line of sight. Our analysis suggests that BAL quasars are more likely to be found in viewing angles close to the equatorial plane of the quasar. However, a pure orientation model is inadequate, and a combination of orientation and evolution is probably the best way to explain the complete BAL phenomena.
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Morrison, Sean, Matthew M. Pieri, Debopam Som und Ignasi Pérez-Ràfols. „Probing large-scale UV background inhomogeneity associated with quasars using metal absorption“. Monthly Notices of the Royal Astronomical Society 506, Nr. 4 (21.07.2021): 5750–63. http://dx.doi.org/10.1093/mnras/stab2091.
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ABSTRACT We study large-scale UV background inhomogeneity in three-dimensions associated with the observed quasar populations at high redshift. We do this by measuring metal absorption through quasar absorption spectrum stacking as a function distance to closest quasar in SDSS-IV/eBOSS on 10 s of comoving megaparsec scales. We study both intergalactic medium absorbers and mixed circumgalactic medium absorbers and probe absorption in O vi, C iv, and Si iv, and Si iii. Overall, stronger high ionization species absorption is seen closer to quasars at 2.4 < z < 3.1. O vi absorption shows a particularly strong change, with effects in C iv evident in some cases, and more marginal effects in Si iii and Si iv. We further study 2.05 < z < 2.4 (with weak signs of increasing homogeneity with time) and explore the study of metal absorption as a function of integrated SDSS-r band flux quasar flux (yielding consistent but less significant results). While the metal absorption does show sensitivity to large-scale 3D quasar proximity, the current incomplete quasar samples limit detailed interpretation. This work does, however, demonstrate that UV background inhomogeneities exist on scales of several 10 s of comoving megaparsecs associated with quasars and that they can be measured with precision by examining metal absorption in the intergalactic medium.
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Bechtold, Jill. „Evolution of the EUV Background from Quasar Absorption Line Studies“. Symposium - International Astronomical Union 168 (1996): 237–44. http://dx.doi.org/10.1017/s0074180900110125.
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The integrated extreme ultraviolet (EUV) radiation from quasars and other high redshift sources provides an ambient ionizing radiation field which may photoionize the gas seen as quasar absorption lines. In particular, the observed evolution of the Lyα forest clouds probably results in part from the evolution of the EUV metagalactic field. Estimates of the EUV field as a function of redshift can be made from measuring the “proximity effect” in quasar spectra; uncertainties in these estimates may be large. Given the uncertainties, the estimated EUV field at z≈3 derived from the proximity effect is in reasonable agreement with the expected contribution from luminous quasars.
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Ahmed, Harum, Ohad Shemmer, Brandon Matthews, Cooper Dix, Trung Ha, Gordon T. Richards, Michael S. Brotherton et al. „Gemini Near Infrared Spectrograph−Distant Quasar Survey: Rest-frame Ultraviolet−Optical Spectral Properties of Broad Absorption Line Quasars“. Astrophysical Journal 968, Nr. 2 (01.06.2024): 77. http://dx.doi.org/10.3847/1538-4357/ad3e69.
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Abstract We present the rest-frame ultraviolet−optical spectral properties of 65 broad absorption line (BAL) quasars from the Gemini Near Infrared Spectrograph−Distant Quasar Survey (GNIRS-DQS). These properties are compared with those of 195 non-BAL quasars from GNIRS-DQS in order to identify the drivers for the appearance of BALs in quasar spectra. In particular, we compare equivalent widths and velocity widths, as well as velocity offsets from systemic redshifts, of principal emission lines. In spite of the differences between their rest-frame ultraviolet spectra, we find that luminous BAL quasars are generally indistinguishable from their non-BAL counterparts in the rest-frame optical band at redshifts 1.55 ≲ z ≲ 3.50. We do not find any correlation between BAL trough properties and the Hβ-based supermassive black hole masses and normalized accretion rates in our sample. Considering the Sloan Digital Sky Survey quasar sample, which includes the GNIRS-DQS sample, we find that a monochromatic luminosity at rest-frame 2500 Å of ≳1045 erg s−1 is a necessary condition for launching BAL outflows in quasars. We compare our findings with other BAL quasar samples and discuss the roles that accretion rate and orientation play in the appearance of BAL troughs in quasar spectra.
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Bañados, Eduardo, Jan-Torge Schindler, Bram P. Venemans, Thomas Connor, Roberto Decarli, Emanuele Paolo Farina, Chiara Mazzucchelli et al. „The Pan-STARRS1 z > 5.6 Quasar Survey. II. Discovery of 55 Quasars at 5.6 < z < 6.5“. Astrophysical Journal Supplement Series 265, Nr. 1 (01.03.2023): 29. http://dx.doi.org/10.3847/1538-4365/acb3c7.
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Abstract The identification of bright quasars at z ≳ 6 enables detailed studies of supermassive black holes, massive galaxies, structure formation, and the state of the intergalactic medium within the first billion years after the Big Bang. We present the spectroscopic confirmation of 55 quasars at redshifts 5.6 < z < 6.5 and UV magnitudes −24.5 < M 1450 < −28.5 identified in the optical Pan-STARRS1 and near-IR VIKING surveys (48 and 7, respectively). Five of these quasars have independently been discovered in other studies. The quasar sample shows an extensive range of physical properties, including 17 objects with weak emission lines, 10 broad absorption line quasars, and 5 objects with strong radio emission (radio-loud quasars). There are also a few notable sources in the sample, including a blazar candidate at z = 6.23, a likely gravitationally lensed quasar at z = 6.41, and a z = 5.84 quasar in the outskirts of the nearby (D ∼ 3 Mpc) spiral galaxy M81. The blazar candidate remains undetected in NOEMA observations of the [C ii] and underlying emission, implying a star formation rate <30–70 M ⊙ yr−1. A significant fraction of the quasars presented here lies at the foundation of the first measurement of the z ∼ 6 quasar luminosity function from Pan-STARRS1 (introduced in a companion paper). These quasars will enable further studies of the high-redshift quasar population with current and future facilities.
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Okoshi, Katsuya, Yosuke Minowa, Nobunari Kashikawa, Toru Misawa, Daichi Kashino, Hajime Sugai, Kazuya Matsubayashi, Atsushi Shimono und Shinobu Ozaki. „Multiple Mg ii Absorption Systems in the Lines of Sight to Quadruply Lensed Quasar H1413+1143“. Astronomical Journal 162, Nr. 5 (04.10.2021): 175. http://dx.doi.org/10.3847/1538-3881/ac0bbb.
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Abstract We find multiple Mg ii absorption systems at redshift z = 1.66, 2.069, and 2.097 in the spatially resolved spectra of the quadruply gravitationally lensed quasar H1413+1143 utilizing the Kyoto tridimensional spectrograph ii (Kyoto 3D ii) spectrograph on board the Subaru telescope. Here we present the first measurement of differences in Mg ii absorption strength of the multiple intervening absorbers, which include ones identified as damped Lyα (DLA) absorption systems. Our detection of the significant Mg ii absorptions in the spatially resolved spectra reveals the inhomogeneous chemical enrichment on scales of about 12 kpc within the separation of the four sight lines. For the DLA system at z = 1.66, the rest equivalent widths (EWs) of the Mg ii absorption lines between the four spatially resolved lines of sight change by factors of up to ∼6, which trace the variations in the H i absorption strength. This suggests that inhomogeneous cold absorbers that give rise to the strong H i/Mg ii absorptions dwell on a scale of about 6–12 kpc between the four lines of sight. We also investigate the degree of variation in the EW of the absorption lines between the lines of sight. We find that the systems giving rise to strong absorptions in the spectra of the quadruply lensed quasars tend to have a high degree of variation in absorption strength between the lines of sight toward the lensed quasars.
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Chartas, George, und Sarah Strickland. „Wide-Angle Quasar Feedback“. Proceedings of the International Astronomical Union 11, S319 (August 2015): 58. http://dx.doi.org/10.1017/s1743921315010145.
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AbstractWe present results from the detection of relativistic winds launched near the innermost stable circular orbits of supermassive black holes. A recent detection of a powerful wind in the X-ray-bright narrow absorption line (NAL) z=1.51 quasar HS 0810+2554 strengthens the case that quasars play a significant role in feedback. In both deep Chandra and XMM-Newton observations of HS 0810 we detected blueshifted absorption lines implying outflowing velocities ranging from 0.1c and 0.4c. The presence of both an emission line at 6.8 keV and an absorption line at 7.8 keV in the spectral line profile of HS 0810 is a characteristic feature of a P-Cygni profile supporting the presence of an expanding outflowing highly ionized Fe absorber. A hard excess component is detected in the XMM-Newton observation of HS 0810 possibly originating from reflection off the disk. Modelling of the XMM-Newton spectrum constrains the inclination angle to be < 35° (68% confidence). The presence of relativistic winds in both low inclination angle NAL quasars as well as in high inclination angle BAL quasars implies that the solid angle of quasar winds may be quite large. The larger solid angle of quasar winds would also indicate that their contribution to the regulation of the host galaxy may be more important than previously thought.
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Dutta, R., S. Raghunathan, N. Gupta und R. Joshi. „uGMRT search for cold gas at z ∼ 1–1.4 towards red quasars“. Monthly Notices of the Royal Astronomical Society 491, Nr. 1 (04.11.2019): 838–47. http://dx.doi.org/10.1093/mnras/stz3084.
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ABSTRACT We present results from our search for H i 21-cm and OH 18-cm absorption at z ∼ 1–1.4 towards red quasars showing strong Mg ii absorption using upgraded Giant Metrewave Radio Telescope. The quasars J1501 + 1822 and J1521 + 5508 show multiple strong associated Mg ii absorption at z ∼ 1.1 and signature of reddening in their optical spectra. We report the detection of H i 21-cm absorption towards J1521 + 5508 at the systemic redshift of the quasar, with $N(\rm{H\,{\small I}}$) = (1.2 ± 0.2) × 1020 cm−2 for spin temperature of 100 K and unit covering factor. The H i 21-cm absorption is offset from the blueshifted strong Mg ii absorbers by ≳1500 km s−1. We do not detect H i 21-cm absorption at the redshift of the associated Mg ii absorption and at the systemic redshift towards J1501 + 1822. We argue that lack of one-to-one correspondence between Mg ii and H i 21-cm absorption could be related with clumpiness of the neutral gas and the radio and optical sightlines probing different volume of the gas. We find that the presence of strong associated Mg ii absorption and reddening in the optical spectra of the quasars lead to an increased detection rate of associated H i 21-cm absorption at z ≥1. We also report non-detection of intervening OH absorption ([OH]/[H i] ≤ (1–4)× 10−8) at z = 1.3 towards two red quasars, J0850 + 5159 and J0852 + 3435, which show strong metal and H i 21-cm absorption and the 2175 Å dust extinction bump.
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Kunert-Bajraszewska, M., M. Cegłowski, C. Roskowiński und M. Gawroński. „Extragalactic jets of broad absorption line (BAL) quasars“. Proceedings of the International Astronomical Union 10, S313 (September 2014): 244–45. http://dx.doi.org/10.1017/s1743921315002264.
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AbstractFast outflows of the ionized plasma, probably lunched in proximity of Supermassive Black Hole, are responsible for blue-shifted Broad Absorption Lines (BALs) in quasar spectrum. Outflows together with powerful jets produced in AGN are important feedback processes. Therefore, understanding physics behind BAL outflows might be a key to comprehend Galaxy Evolution as a whole. Discovery of the existence of radio-loud BAL quasars gave us another opportunity to study the BAL phenomenon, this time on the ground on radio emission. The radio emission is an additional tool to understand the BAL quasars, their orientation and age, by the VLBI imaging (detection of radio jets and their direction, size determination), the radio-loudness parameter distribution and variability study.
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Yang, Jinyi, Feige Wang, Xiaohui Fan, Aaron J. Barth, Joseph F. Hennawi, Riccardo Nanni, Fuyan Bian et al. „Probing Early Supermassive Black Hole Growth and Quasar Evolution with Near-infrared Spectroscopy of 37 Reionization-era Quasars at 6.3 < z ≤ 7.64“. Astrophysical Journal 923, Nr. 2 (01.12.2021): 262. http://dx.doi.org/10.3847/1538-4357/ac2b32.
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Abstract We report the results of near-infrared spectroscopic observations of 37 quasars in the redshift range 6.3 < z ≤ 7.64, including 32 quasars at z > 6.5, forming the largest quasar near-infrared spectral sample at this redshift. The spectra, taken with Keck, Gemini, VLT, and Magellan, allow investigations of central black hole mass and quasar rest-frame ultraviolet spectral properties. The black hole masses derived from the Mg ii emission lines are in the range (0.3–3.6) × 109 M ⊙, which requires massive seed black holes with masses ≳103–104 M ⊙, assuming Eddington accretion since z = 30. The Eddington ratio distribution peaks at λ Edd ∼ 0.8 and has a mean of 1.08, suggesting high accretion rates for these quasars. The C iv–Mg ii emission-line velocity differences in our sample show an increase of C iv blueshift toward higher redshift, but the evolutionary trend observed from this sample is weaker than the previous results from smaller samples at similar redshift. The Fe ii/Mg ii flux ratios derived for these quasars up to z = 7.6, compared with previous measurements at different redshifts, do not show any evidence of strong redshift evolution, suggesting metal-enriched environments in these quasars. Using this quasar sample, we create a quasar composite spectrum for z > 6.5 quasars and find no significant redshift evolution of quasar broad emission lines and continuum slope, except for a blueshift of the C iv line. Our sample yields a strong broad absorption line quasar fraction of ∼24%, higher than the fractions in lower-redshift quasar samples, although this could be affected by small sample statistics and selection effects.
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Yang, Jinyi, Xiaohui Fan, Ansh Gupta, Adam D. Myers, Nathalie Palanque-Delabrouille, Feige Wang, Christophe Yèche et al. „DESI z ≳ 5 Quasar Survey. I. A First Sample of 400 New Quasars at z ∼ 4.7–6.6“. Astrophysical Journal Supplement Series 269, Nr. 1 (01.11.2023): 27. http://dx.doi.org/10.3847/1538-4365/acf99b.
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Abstract We report the first results of a high-redshift (z ≳ 5) quasar survey using the Dark Energy Spectroscopic Instrument (DESI). As a DESI secondary target program, this survey is designed to carry out a systematic search and investigation of quasars at 4.8 < z < 6.8. The target selection is based on the DESI Legacy Imaging Surveys (the Legacy Surveys) DR9 photometry, combined with the Pan-STARRS1 data and J-band photometry from public surveys. A first quasar sample has been constructed from the DESI Survey Validation 3 (SV3) and first-year observations until 2022 May. This sample includes more than 400 new quasars at redshift 4.7 ≤ z < 6.6, down to 21.5 magnitude (AB) in the z band, discovered from 35% of the entire target sample. Remarkably, there are 220 new quasars identified at z ≥ 5, more than one-third of existing quasars previously published at this redshift. The observations so far result in an average success rate of 23% at z > 4.7. The current spectral data set has already allowed analysis of interesting individual objects (e.g., quasars with damped Lyα absorbers and broad absorption line features), and statistical analysis will follow the survey’s completion. A set of science projects will be carried out leveraging this program, including quasar luminosity function, quasar clustering, intergalactic medium, quasar spectral properties, intervening absorbers, and properties of early supermassive black holes. Additionally, a sample of 38 new quasars at z ∼ 3.8–5.7 discovered from a pilot survey in the DESI SV1 is also published in this paper.
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Vivek, M. „Ionization-driven intrinsic absorption line variability of BAL quasars in the Stripe 82 region“. Monthly Notices of the Royal Astronomical Society 486, Nr. 2 (03.04.2019): 2379–96. http://dx.doi.org/10.1093/mnras/stz947.
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Abstract We investigate the connection between the intrinsic C iv absorption line variability and the continuum flux changes of broad absorption line (BAL) quasars using a sample of 78 sources in the Stripe 82 region. The absorption trough variability parameters are measured using the archival multi-epoch spectroscopic data from the Sloan Digital Sky Survey (SDSS), and the continuum flux variability parameters are estimated from the photometric light curves obtained by the SDSS and the Catalina Real-Time Survey surveys. We find evidence for weak correlations (ρs ∼ 0.3) between the intrinsic C iv absorption line variability and the quasar continuum variability for the final sample of 78 BAL quasars. The correlation strengths improve (ρs ∼ 0.5) for the ‘high-signal-to-noise ratio (SNR)’ sample sources that have higher spectral SNR. Using two subsets of the high-SNR sample differing on the absorption trough depth, we find that the shallow-trough subset shows an even stronger correlation (ρs ∼ 0.6), whereas the deep-trough subset does not show any correlation between the absorption line variability and the continuum variability. These results point to the important role of saturation effects in the correlation between the absorption line variability and the continuum variability of BAL quasars. Considering other effects that can also smear the correlation, we conclude that the actual correlation between the absorption line and continuum variability is even stronger.
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Rees, Martin J. „What Quasars Tell Us about Galactic Evolution“. Symposium - International Astronomical Union 171 (1996): 303–11. http://dx.doi.org/10.1017/s0074180900232531.
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Quasars offer three types of clue to galactic evolution. (i) The formation of massive black holes in the centres of young galaxies; (ii) Clues to subgalactic structure from quasar absorption spectra; (iii) Implications for redshifts higher than 5. These are briefly summarised in this text.
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Monadi, Reza, und Simeon Bird. „Improved selection of extremely red quasars with boxy C iv lines in BOSS“. Monthly Notices of the Royal Astronomical Society 511, Nr. 3 (03.02.2022): 3501–13. http://dx.doi.org/10.1093/mnras/stac294.
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ABSTRACT Extremely red quasars (ERQs) are an interesting sample of quasars in the Baryon Oscillation Spectroscopic Sample (BOSS) in the redshift range of 2.0–3.4 and have extreme red colours of i − W3 ≥ 4.6. Core ERQs have strong C iv emission lines with rest equivalent width of ≥100 Å. Many core ERQs also have C iv line profiles with peculiar boxy shapes which distinguish them from normal blue quasars. We show, using a combination of kernel density estimation and local outlier factor analyses on a space of the i − W3 colour, C iv rest equivalent width and line kurtosis, that core ERQs likely represent a separate population rather than a smooth transition between normal blue quasars and the quasars in the tail of the colour-REW distribution. We apply our analyses to find new criteria for selecting ERQs in this 3D parameter space. Our final selection produces 133 quasars, which are three times more likely to have a visually verified C iv broad absorption line feature than the previous core ERQ sample. We further show that our newly selected sample are extreme objects in the intersection of the WISE AGN catalogue with the MILLIQUAS quasar catalogue in the colour–colour space of (W1 − W2, W2 − W3). This paper validates an improved selection method for red quasars which can be applied to future data sets such as the quasar catalogue from the Dark Energy Spectroscopic Instrument.
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Levshakov, S. A. „Absorption spectra of quasars“. Astrophysics 29, Nr. 2 (1989): 657–71. http://dx.doi.org/10.1007/bf01005972.
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Curran, S. J., J. K. Webb, M. T. Murphy, R. Bandiera, E. Corbelli und V. V. Flambaum. „A Catalogue of Damped Lyman Alpha Absorption Systems and Radio Flux Densities of the Background Quasars“. Publications of the Astronomical Society of Australia 19, Nr. 4 (2002): 455–74. http://dx.doi.org/10.1071/as01077.
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AbstractWe present a catalogue of the 322 damped Lyman alpha absorbers taken from the literature. All damped Lyman alpha absorbers are included, with no selection on redshift or quasar magnitude. Of these, 123 are candidates and await confirmation using high resolution spectroscopy. For all 322 objects we catalogue the radio properties of the background quasars, where known. Around 60 quasars have radio flux densities above 0.1 Jy and approximately half of these have optical magnitudes brighter than V = 18. This compilation should prove useful in several areas of extragalactic/cosmological research.
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Gross, Arran C., Yu-Ching Chen, Adi Foord, Xin Liu, Yue Shen, Masamune Oguri, Andy Goulding et al. „Varstrometry for Off-nucleus and Dual Subkiloparsec Active Galactic Nuclei (VODKA): Investigating the Nature of SDSS J0823+2418 at z = 1.81, A Likely Lensed Quasar“. Astrophysical Journal 956, Nr. 2 (01.10.2023): 117. http://dx.doi.org/10.3847/1538-4357/acf469.
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Abstract Dual quasars at small physical separations are an important precursor phase of galaxy mergers, ultimately leading to the coalescence of the two supermassive black holes. Starting from a sample of dual and/or lensed quasar candidates discovered using astrometric jitter in Gaia data, we present a pilot case study of one of the most promising yet puzzling candidate dual quasars at cosmic noon (z ∼ 1.8). Using multiwavelength imaging and spectroscopy from X-ray to radio, we test whether the SDSS J0823+2418 system is two individual quasars in a bound pair at separation ∼0.″64, or instead a single quasar being gravitationally lensed by a foreground galaxy. We find consistent flux ratios (∼1.25−1.45) between the two sources in optical, near-IR (NIR), UV, and radio, and thus similar spectral energy distributions, suggesting a strong-lensing scenario. However, differences in the radio spectral index, as well as changing X-ray fluxes, hint at either a dual quasar with otherwise nearly identical properties or perhaps lensing-based time lag of ∼3 days paired with intrinsic variability. We find with lens mass modeling that the relative NIR positions and magnitudes of the two quasars and a marginally detected central galaxy are consistent with strong lensing. Archival Sloan Digital Sky Survey spectra likewise suggest a foreground absorber via Mg ii absorption lines. We conclude that SDSS J0823+2418 is likely a lensed quasar, and therefore that the VODKA sample contains a population of these lensed systems (perhaps as high as 50%) as well as dual quasars.
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Timlin, John D., W. N. Brandt, S. Zhu, H. Liu, B. Luo und Q. Ni. „The frequency of extreme X-ray variability for radio-quiet quasars“. Monthly Notices of the Royal Astronomical Society 498, Nr. 3 (02.09.2020): 4033–50. http://dx.doi.org/10.1093/mnras/staa2661.
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ABSTRACT We analyse 1598 serendipitous Chandra X-ray observations of 462 radio-quiet quasars to constrain the frequency of extreme amplitude X-ray variability that is intrinsic to the quasar corona and innermost accretion flow. The quasars in this investigation are all spectroscopically confirmed, optically bright (mi ≤ 20.2), and contain no identifiable broad absorption lines in their optical/ultraviolet spectra. This sample includes quasars spanning z ≈ 0.1–4 and probes X-ray variability on time-scales of up to ≈12 rest-frame years. Variability amplitudes are computed between every epoch of observation for each quasar and are analysed as a function of time-scale and luminosity. The tail-heavy distributions of variability amplitudes at all time-scales indicate that extreme X-ray variations are driven by an additional physical mechanism and not just typical random fluctuations of the coronal emission. Similarly, extreme X-ray variations of low-luminosity quasars seem to be driven by an additional physical mechanism, whereas high-luminosity quasars seem more consistent with random fluctuations. The amplitude at which an X-ray variability event can be considered extreme is quantified for different time-scales and luminosities. Extreme X-ray variations occur more frequently at long time-scales (Δt ≳ 300 d) than at shorter time-scales and in low-luminosity quasars compared to high-luminosity quasars over a similar time-scale. A binomial analysis indicates that extreme intrinsic X-ray variations are rare, with a maximum occurrence rate of $\lt 2.4{{\ \rm per\ cent}}$ of observations. Finally, we present X-ray variability and basic optical emission-line properties of three archival quasars that have been newly discovered to exhibit extreme X-ray variability.
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Pâris, Isabelle, Patrick Petitjean, Éric Aubourg, Adam D. Myers, Alina Streblyanska, Brad W. Lyke, Scott F. Anderson et al. „The Sloan Digital Sky Survey Quasar Catalog: Fourteenth data release“. Astronomy & Astrophysics 613 (Mai 2018): A51. http://dx.doi.org/10.1051/0004-6361/201732445.
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We present the data release 14 Quasar catalog (DR14Q) from the extended Baryon Oscillation Spectroscopic Survey (eBOSS) of the Sloan Digital Sky Survey IV (SDSS-IV). This catalog includes all SDSS-IV/eBOSS objects that were spectroscopically targeted as quasar candidates and that are confirmed as quasars via a new automated procedure combined with a partial visual inspection of spectra, have luminosities Mi [z = 2] < −20.5 (in a Λ CDM cosmology with H0 = 70 km s−1 Mpc−1, Ω M =0.3, and Ω Λ = 0.7), and either display at least one emission line with a full width at half maximum larger than 500 km s−1 or, if not, have interesting/complex absorption features. The catalog also includes previously spectroscopically-confirmed quasars from SDSS-I, II, and III. The catalog contains 526 356 quasars (144 046 are new discoveries since the beginning of SDSS-IV) detected over 9376 deg2 (2044 deg2 having new spectroscopic data available) with robust identification and redshift measured by a combination of principal component eigenspectra. The catalog is estimated to have about 0.5% contamination. Redshifts are provided for the Mg II emission line. The catalog identifies 21 877 broad absorption line quasars and lists their characteristics. For each object, the catalog presents five-band (u, g, r, i, z) CCD-based photometry with typical accuracy of 0.03 mag. The catalog also contains X-ray, ultraviolet, near-infrared, and radio emission properties of the quasars, when available, from other large-area surveys. The calibrated digital spectra, covering the wavelength region 3610–10 140 Å at a spectral resolution in the range 1300 < R < 2500, can be retrieved from the SDSS Science Archiver Server.
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Cai, Zhenyi. „The Composite Spectral Energy Distribution of Quasars Is Surprisingly Universal Since Cosmic Noon“. Universe 10, Nr. 11 (19.11.2024): 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 composite quasar SED is plausibly also independent of black hole mass and Eddington ratio, and suggests similar properties of dust and gas in the quasar host galaxies since cosmic noon. Both the mean and median composite SEDs are nicely consistent with previous mean composite quasar spectra at wavelengths beyond ≃1000 A˚, but at shorter wavelengths, are redder, indicating, on average, less ionizing radiation than previously expected. Through comparing the model-predicted to the observed composite quasar SEDs, we favor a simply truncated disk model, rather than a standard thin disk model, for the quasar central engine, though we request more sophisticated disk models. Future deep ultraviolet facilities, such as the China Space Station Telescope and the Ultraviolet Explorer, would prompt revolutions in many aspects, including the quasar central engine, production of the broad emission lines in quasars, and cosmic reionization.
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Shull, J. Michael. „High-Resolution Spectroscopy of Quasars and Quasar Absorption-Line Systems“. Publications of the Astronomical Society of the Pacific 107 (Oktober 1995): 1007. http://dx.doi.org/10.1086/133653.
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Lewis, Tiffany R., und Doron Chelouche. „On the Fine-tuning and Physical Origin of Line-locked Absorption Systems in Active Galaxies“. Astrophysical Journal 945, Nr. 2 (01.03.2023): 110. http://dx.doi.org/10.3847/1538-4357/acb541.
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Abstract Line locking (LL) of absorption-line systems is a clear signature of the dynamical importance of radiation-pressure force in driving astrophysical flows, with recent findings suggesting that it may be common in quasars exhibiting multiple intrinsic narrow absorption-line (NAL) systems. In this work, we probe the phase space conducive to LL and follow the detailed kinematics of those systems that may lock at the velocity separation of the C iv λ λ1548.19, 1550.77 doublet. We find that a small volume of the phase-phase admits LL, suggesting a high degree of fine-tuning between the physical properties of locked systems. The stability of LL against quasar luminosity variations is quantified with implications for the long-term variability amplitude of quasars and the velocity-separation statistic between multiple NAL systems. The high occurrence of LL by the C iv doublet implies that the hidden extreme-UV emission from quasars is unlikely to be significantly underestimated by current models. Further, the ratio of the LL velocity to the outflow velocity may serve as a powerful constraint on the composition of the accelerating medium. We conclude that LL poses significant challenges to current theories for the formation of nonintervening NAL systems, and speculate that it may be a manifestation of expanding circumstellar shells around asymptotic giant branch stars in the quasar-host bulge.
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Yi, Weimin, P. B. Hall, Zunli Yuan, W. N. Brandt, D. P. Schneider, Zhicheng He, Jin-Ming Bai und Xue-Bing Wu. „Quasar Winds Caught on Acceleration and Deceleration“. Astrophysical Journal Supplement Series 271, Nr. 2 (01.04.2024): 61. http://dx.doi.org/10.3847/1538-4365/ad2a42.
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Abstract We present an observational study of wind acceleration based on four low-ionization broad absorption line (BAL) quasars (J0136, J1238, J1259, and J1344). J0136 and J1344 (group 1) are radio-quiet and show large BAL-velocity shifts as opposed to stable line-locking associated absorption lines (AALs). Notably, J1344 displays a linear relation between BAL-velocity shift and time interval over three consecutive epochs, characteristic of compelling evidence for BAL acceleration. J1238 and J1259 (group 2) exhibit small BAL-velocity shifts along with steep-spectrum, weak radio emission at 3.0 and 1.4 GHz. All four quasars have spectral energy distributions (SEDs) with a peak at λ rest ∼ 10 μm, suggesting a link between the BAL acceleration and hot dust emission. The group-2 quasars are redder than group-1 quasars and have a steeper rise at 1 μm < λ rest < 3 μm in their SEDs. All but J1238 exhibit a steep rise followed by a plateau-like time evolution in BAL-velocity shift. Our investigations, combined with previous studies of BAL acceleration, indicate that (1) the coupling process between the BALs and the interstellar medium (ISM) is one of the major avenues for the origin of quasar reddening and patchy obscuration, (2) AAL outflows are ubiquitous and likely signify large-scale remnants of BAL winds coupled to the ISM, and (3) wind deceleration that is closely linked to the BAL–ISM coupling process may produce weak radio emission in otherwise radio-quiet quasars.
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Fumagalli, Michele, Sotiria Fotopoulou und Laura Thomson. „Detecting neutral hydrogen at z ≳ 3 in large spectroscopic surveys of quasars“. Monthly Notices of the Royal Astronomical Society 498, Nr. 2 (31.08.2020): 1951–62. http://dx.doi.org/10.1093/mnras/staa2388.
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ABSTRACT We present a pipeline based on a random forest classifier for the identification of high column density clouds of neutral hydrogen (i.e. the Lyman limit systems, LLSs) in absorption within large spectroscopic surveys of z ≳ 3 quasars. We test the performance of this method on mock quasar spectra that reproduce the expected data quality of the Dark Energy Spectroscopic Instrument and the WHT (William Herschel Telescope) Enhanced Area Velocity Explorer surveys, finding ${\gtrsim}90{{\ \rm per\ cent}}$ completeness and purity for $N_{\rm H\,\rm{\small I}} \gtrsim 10^{17.2}~\rm cm^{-2}$ LLSs against quasars of g < 23 mag at z ≈ 3.5–3.7. After training and applying our method on 10 000 quasar spectra at z ≈ 3.5–4.0 from the Sloan Digital Sky Survey (Data Release 16), we identify ≈6600 LLSs with $N_{\rm H\,\rm{\small I}} \gtrsim 10^{17.5}~\rm cm^{-2}$ between z ≈ 3.1 and 4.0 with a completeness and purity of ${\gtrsim}90{{\ \rm per\ cent}}$ for the classification of LLSs. Using this sample, we measure a number of LLSs per unit redshift of ℓ(z) = 2.32 ± 0.08 at z = [3.3, 3.6]. We also present results on the performance of random forest for the measurement of the LLS redshifts and H i column densities, and for the identification of broad absorption line quasars.
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Timlin, John D., W. N. Brandt, Q. Ni, B. Luo, Xingting Pu, D. P. Schneider, M. Vivek und W. Yi. „The correlations between optical/UV broad lines and X-ray emission for a large sample of quasars“. Monthly Notices of the Royal Astronomical Society 492, Nr. 1 (06.12.2019): 719–41. http://dx.doi.org/10.1093/mnras/stz3433.
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ABSTRACT We present Chandra observations of 2106 radio-quiet quasars in the redshift range 1.7 ≤ z ≤ 2.7 from the Sloan Digital Sky Survey (SDSS), through data release 14 (DR14), that do not contain broad absorption lines in their rest-frame ultraviolet (UV) spectra. This sample adds over a decade worth of SDSS and Chandra observations to our previously published sample of 139 quasars from SDSS DR5 that is still used to correlate X-ray and optical/UV emission in typical quasars. We fit the SDSS spectra for 753 of the quasars in our sample that have high-quality (exposure time ≥ 10 ks and off-axis observation angle ≤ 10 arcmin) X-ray observations, and analyse their X-ray-to-optical spectral energy distribution properties (αox and Δαox) with respect to the measured C iv and Mg ii emission-line rest-frame equivalent width (EW) and the C iv emission-line blueshift. We find significant correlations (at the ≥99.99 per cent level) between αox and these emission-line parameters, as well as between Δαox and $\rm{C \, \small{IV}}$ EW. Slight correlations are found between Δαox and $\rm{C \, \small{IV}}$ blueshift, $\rm{Mg \, \small{II}}$ EW, and the $\rm{C \, \small{IV}}$ EW to $\rm{Mg \, \small{II}}$ EW ratio. The best-fitting trend in each parameter space is used to compare the X-ray weakness (Δαox) and optical/UV emission properties of typical quasars and weak-line quasars (WLQs). The WLQs typically exhibit weaker X-ray emission than predicted by the typical quasar relationships. The best-fitting relationships for our typical quasars are consistent with predictions from the disc–wind quasar model. The behaviour of the WLQs compared to our typical quasars can be explained by an X-ray ‘shielding’ model.
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Hamann, Fred, und Leah E. Simon. „Quasar Metal Abundances & Host Galaxy Evolution“. Proceedings of the International Astronomical Union 5, S265 (August 2009): 171–78. http://dx.doi.org/10.1017/s1743921310000487.
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AbstractHigh-redshift quasars provide a unique glimpse into the early evolution of massive galaxies. The physical processes that trigger major bursts of star formation in quasar host galaxies (mergers and interactions) probably also funnel gas into the central regions to grow the super-massive black holes (SMBHs) and ignite the luminous quasar phenomenon. The globally dense environments where this occurs were probably also among the first to collapse and manufacture stars in significant numbers after the big bang. Measurements of the elemental abundances near quasars place important constraints on the nature, timing and extent of this star formation. A variety of studies using independent emission and absorption line diagnostics have shown that quasar environments have gas-phase metallicities that are typically a few times solar at all observed redshifts. These results are consistent with galaxy evolution scenarios in which large amounts of star formation (e.g., in the central regions) precede the visibly bright quasar phase. An observed trend for higher metallicities in more luminmous quasars (powered by more massive SMBHs) is probably tied to the well-known mass–metallicity relation among ordinary galaxies. This correlation and the absence of a trend with redshift indicate that mass is a more important parameter in the evolution than the time elapsed since the big bang.
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Stone, Robert B., und Gordon T. Richards. „Narrow, intrinsic C iv absorption in quasars as it relates to outflows, orientation, and radio properties“. Monthly Notices of the Royal Astronomical Society 488, Nr. 4 (05.08.2019): 5916–34. http://dx.doi.org/10.1093/mnras/stz2111.
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Abstract This work provides evidence that a large fraction of C iv narrow absorption lines (NALs) seen along the line of sight to distant quasars are due to accretion disc winds, while also seeking to understand the relationship between NALs and certain quasar-intrinsic properties. We extend the results from past work in the literature using ${\sim}105\, 000$ NALs from a sample of ${\sim}58\, 000$ SDSS quasars. The primary results of this work are summarized as follows: (1) the velocity distribution (dN/dβ) of NALs is not a function of radio loudness (or even detection) once marginalized by optical/UV luminosity; (2) there are significant differences in the number and distribution of NALs as a function of both radio spectral index and optical/UV luminosity, and these two findings are not entirely interdependent; (3) improvements in quasar systemic redshift measurements and differences in the NAL distribution as a combined function of optical luminosity and radio spectral index together provide evidence that a significant portion of NALs are due to outflows; (4) the results are consistent with standard models of accretion disc winds governed by the LUV–αox relationship and line-of-sight orientation indicated by radio spectral index, and (5) possibly support a magnetically arrested disc model as an explanation for the semistochastic nature of strong radio emission in a fraction of quasars.
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Heintz, K. E., J. P. U. Fynbo, E. Høg, P. Møller, J. K. Krogager, S. Geier, P. Jakobsson und L. Christensen. „Unidentified quasars among stationary objects from Gaia DR2“. Astronomy & Astrophysics 615 (Juli 2018): L8. http://dx.doi.org/10.1051/0004-6361/201833396.
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Here we apply a technique selecting quasar candidates purely as sources with zero proper motions in the Gaia data release 2 (DR2). We demonstrate that this approach is highly efficient toward high Galactic latitudes with ≲25% contamination from stellar sources. Such a selection technique offers very pure sample completeness, since all cosmological point sources are selected regardless of their intrinsic spectral properties within the limiting magnitude of Gaia. We carry out a pilot-study, defining a sample compiled by including all Gaia-DR2 sources within one degree of the north Galactic pole (NGP) selected to have proper motions consistent with zero within 2σ uncertainty. By cross-matching the sample to the optical Sloan Digital Sky Survey (SDSS) and the mid-infrared (MIR) AllWISE photometric catalogues, we investigate the colours of each of our sources. We determine the efficiency of our selection by comparison with previously spectroscopically confirmed quasars. The majority of the zero-proper-motion sources selected here have optical to MIR colours consistent with known quasars. The remaining population may be contaminating stellar sources, but some may also be quasars with colours similar to stars. Spectroscopic follow-up of the zero-proper-motion sources is needed to unveil such a hitherto hidden quasar population. This approach has the potential to allow substantial progress on many important questions concerning quasars, such as determining the fraction of dust-obscured quasars, the fraction of broad absorption line (BAL) quasars, and the metallicity distribution of damped Lyman-α absorbers. The technique could also potentially reveal new types of quasars or even new classes of cosmological point sources.
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Arrigoni Battaia, F., A. Obreja, J. X. Prochaska, J. F. Hennawi, H. Rahmani, E. Bañados, E. P. Farina, Z. Cai und A. Man. „Discovery of intergalactic bridges connecting two faint z ∼ 3 quasars“. Astronomy & Astrophysics 631 (11.10.2019): A18. http://dx.doi.org/10.1051/0004-6361/201936211.
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We used the Multi-Unit Spectroscopic Explore (MUSE) on the Very Large Telescope (VLT) to conduct a survey of z ∼ 3 physical quasar pairs at close separation (<30″) with a fast observation strategy (45 min on source). Our aim is twofold: (i) to explore the Lyα glow around the faint-end of the quasar population; and (ii) to take advantage of the combined illumination of a quasar pair to unveil large-scale intergalactic structures (if any) extending between the two quasars. In this work we report the results for the quasar pair SDSS J113502.03−022110.9 – SDSS J113502.50−022120.1 (z = 3.020, 3.008; i = 21.84, 22.15), separated by 11.6″ (or 89 projected kpc). MUSE reveals filamentary Lyα structures extending between the two quasars with an average surface brightness of SBLyα = 1.8 × 10−18 erg s−1 cm−2 arcsec−2. Photoionization models of the constraints in the Lyα, He IIλ1640, and C IVλ1548 line emissions show that the emitting structures are intergalactic bridges with an extent between ∼89 kpc, the quasars’ projected distance, and up to ∼600 kpc. Our models rule out the possibility that the structure extends for ∼2.9 Mpc, that is, the separation inferred from the uncertain systemic redshift difference of the quasars if the difference was only due to the Hubble flow. At the current spatial resolution and surface brightness limit, the average projected width of an individual bridge is ∼35 kpc. We also detect one strong absorption in H I, N V, and C IV along the background sight-line at higher z, which we interpret to be due to at least two components of cool (T ∼ 104 K), metal enriched (Z > 0.3 Z⊙), and relatively ionized circumgalactic or intergalactic gas surrounding the quasar pair. Two additional H I absorbers are detected along both quasar sight-lines at ∼−900 and −2800 km s−1 from the system; the latter has associated C IV absorption only along the foreground quasar sight-line. The absence of galaxies in the MUSE field of view at the redshifts of these two absorbers suggests that they trace large-scale structures or expanding shells in front of the quasar pair. Combining longer exposures and higher spectral resolution when targeting similar quasar pairs has the potential to firmly constrain the physical properties of gas in large-scale intergalactic structures.
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Culliton, Chris, Jane Charlton, Mike Eracleous, Rajib Ganguly und Toru Misawa. „Probing quasar winds using intrinsic narrow absorption lines“. Monthly Notices of the Royal Astronomical Society 488, Nr. 4 (07.08.2019): 4690–731. http://dx.doi.org/10.1093/mnras/stz1642.
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ABSTRACT We use the spectra of 73 quasars (1.5 ≲ z ≲ 5) from the VLT UVES archive to catalogue and study narrow absorption lines (NALs) that are physically associated with (intrinsic to) the quasars. We identify 410 NAL systems containing C iv, N v, and/or Si iv doublets. Based on the assumption that only systems intrinsic to the quasar can exhibit partial coverage of the background source(s), we identify 34 reliably intrinsic NAL systems and 11 systems that are potentially intrinsic, as well as 4 mini-broad absorption lines (BALs) and 1 BAL. The minimum fraction of quasars with at least one intrinsic system is shown to be 38 per cent. We identify intrinsic NALs with a wide range of properties, including apparent ejection velocity, coverage fraction, and ionization level. There is a continuous distribution of properties, rather than discrete families, ranging from partially covered C iv systems with black Ly α and with a separate low-ionization gas phase to partially covered N v systems with partially covered Ly α and without detected low-ionization gas. Even more highly ionized associated and intrinsic absorption systems (O vi, Ne viii, and Mg x doublets) have been presented in separate studies; these may represent an extension of the above sequence. We also use the properties of the NALs in conjunction with recent models of accretion disc winds that predict the origins of the absorbing gas in order to determine the model that best characterizes our sample. Additionally, we construct a model describing the spatial distributions, geometries, and varied ionization structures of intrinsic NALs.