Insight into quasar ages may be obtained from the proximity effect, but so far only in a limited number of bright quasars. Based on ~2600 SDSS quasar spectra at 2.5 <= z <= 3.5, a search for spectral voids between Ly-alpha forest lines finds proximity zones over a wide range of radial distances. The majority of zone sizes are less than 5 Mpc, with their numbers decreasing exponentialy towards larger distances. After normalization by luminosities, the zone sizes are distributed an e-folding scale of 0.64 as compared with the anticipated values. A group of quasars are selected for their large proximity zones of >~ 10 Mpc. Their composite spectrum displays strong narrow cores and large equivalent widths in Ly-alpha and other major UV emission lines. If the proximity zones along lines of sight are indicative of quasar ages, these features may be the signatures of old quasars. Another group of quasars are selected as they show no proximity zone and exhibit intrinsic absorption lines at z_{ab} > z_{em}. They are likely young quasars and exhibit weaker narrow emission-line components. The significant difference of spectral features between the two groups may reflect an evolution pattern over quasars' lifetimes.
Motivated by recent measurements of the number density of faint AGN at high redshift, we investigate the contribution of quasars to reionization by tracking the growth of central supermassive black holes in an update of the Meraxes semi-analytic model. The model is calibrated against the observed stellar mass function at $z\sim0.6-7$, the black hole mass function at $z\lesssim0.5$, the global ionizing emissivity at $z\sim2-5$ and the Thomson scattering optical depth. The model reproduces a Magorrian relation in agreement with observations at $z<0.5$ and predicts a decreasing black hole mass to…
We present new rest frame UV and visible observations of 22 high-redshift (1 < z < 2.5) 3C radio galaxies and QSOs obtained with the Hubble Space Telescope's (HST) Wide Field Camera 3 (WFC3) instrument. Using a custom data reduction strategy in order to assure the removal of cosmic rays, persistence signal, and other data artifacts, we have produced high-quality science-ready images of the targets and their local environments. We observe targets with regions of UV emission suggestive of active star formation. In addition, several targets exhibit highly distorted host galaxy morphologies in the…
Using 16,421 spectra from a sample of 340 quasars ($1.62<z<3.30$) from the SDSS Reverberation Mapping Project, we present an analysis of quasar spectral variability. We confirm the intrinsic Baldwin Effect and brighter-means-bluer trends in which emission line strength and color are associated with changes in luminosity. We then create a composite differential spectrum that captures the wavelength dependence of quasar variability as a function of change in luminosity. When using a bandpass around 1740 Å to describe the luminosity, the differential spectrum follows a power law at longer wavelen…
Increasing evidence suggests that He II proximity profiles in the quasar spectra at z ~ 3 - 4 are sensitive probes of quasar ages. But the development of their H I counterparts is difficult to trace and remains poorly constrained. We compare the UV spectra of 15 He II quasars with their high-resolution optical counterparts and find a significant correlation between the sizes of He II and H I proximity zones. The luminous quasar HE2347-4342 displays a null proximity zone in both He II and H I, suggesting that it is extremely young (age < 0.2 Myr). Three other quasars also display small proximit…
The aim of this paper is to investigate the claim that stars in the lensing galaxy of a gravitationally lensed quasar system can always account for the observed microlensing of the individual quasar images. A small sample of gravitationally lensed quasar systems was chosen where the quasar images appear to lie on the fringe of the stellar distribution of the lensing galaxy. As with most quasar systems, all the individual quasar images were observed to be microlensed. The surface brightness of the lensing galaxy at the positions of the quasar images was measured from HST frames, and converted t…
We present optical spectroscopy of the close companions of 22 low redshift (z<0.5) quasars (QSO) selected from a larger sample of QSO in the SDSS Stripe82 region for which both the host galaxy and the large scale environments have been investigated in our previous work. The new observations extend the number of QSO studied in our previous paper on close companion galaxies of 12 quasars. Our analysis here covers all 34 quasars from both this work and the previously published paper. We find that half of them (15 QSO; $\sim$44%) have at least one associated galaxy. Many (12 galaxies; $\sim$67%) o…
We use the Dark-ages, Reionization And Galaxy-formation Observables from Numerical Simulations (DRAGONS) framework to investigate the effect of galaxy-formation physics on the morphology and statistics of ionized hydrogen (HII) regions during the Epoch of Reioinization (EoR). DRAGONS self-consistently couples a semi-analytic galaxy-formation model with the inhomogeneous ionizing UV background, and can therefore be used to study the dependence of morphology and statistics of reionization on feedback phenomena of the ionizing source galaxy population. Changes in galaxy-formation physics modify t…
We study the application of machine learning techniques for the detection of the astrometric signature of dark matter substructure. In this proof of principle a population of dark matter subhalos in the Milky Way will act as lenses for sources of extragalactic origin such as quasars. We train {\it ResNet-18}, a state-of-the-art convolutional neural network to classify angular velocity maps of a population of quasars into lensed and no lensed classes. We show that an SKA -like survey with extended operational baseline can be used to probe the substructure content of the Milky Way, and demonstra…
The HeII transverse proximity effect - enhanced HeII Lyα transmission in a background sightline caused by the ionizing radiation of a foreground quasar - offers a unique opportunity to probe the emission properties of quasars, in particular the emission geometry (obscuration, beaming) and the quasar lifetime. Building on the foreground quasar survey published in Schmidt+2017, we present a detailed model of the HeII transverse proximity effect, specifically designed to include light travel time effects, finite quasar ages, and quasar obscuration. We post-process outputs from a cosmological hydr…
We investigate the flux ratio between the 1335 A and 2326 A lines of singly ionized carbon in the extended narrow line regions of type 2 quasars at z~2.5. We find the observed CII 1335 / CII] 2326 flux ratio, which is not sensitive to the C/H abundance ratio, to be often several times higher than predicted by the canonical AGN photoionization models that use solar metallicity and a Maxwell-Boltzmann electron energy distribution. We study several potential solutions for this discrepancy: low gas metallicity, shock ionization, continuum fluorescence, and kappa-distributed electron energies. Alth…
We report on the diversity in quasar spectra from the Baryon Oscillation Spectroscopic Survey. After filtering the spectra to mitigate selection effects and Malmquist bias associated with a nearly flux-limited sample, we create high signal-to-noise ratio composite spectra from 58,656 quasars (2.1 \le z \le 3.5), binned by luminosity, spectral index, and redshift. With these composite spectra, we confirm the traditional Baldwin effect (BE, i.e., the anticorrelation of C IV equivalent width (EW) and luminosity) that follows the relation W_λ\propto L^{β_w} with slope β_w = -0.35 \pm 0.004, -0.35 …
The presence of multifractality in a time series shows different correlations for different time scales as well as intermittent behaviour that cannot be captured by a single scaling exponent. The identification of a multifractal nature allows for a characterization of the dynamics and of the intermittency of the fluctuations in non-linear and complex systems. In this study, we search for a possible multifractal structure (multifractality signature) of the flux variability in the quasar 3C 273 time series for all electromagnetic wavebands at different observation points, and the origins for the…
We use a background quasar to detect the presence of circum-galactic gas around a $z=0.91$ low-mass star forming galaxy. Data from the new Multi Unit Spectroscopic Explorer (MUSE) on the VLT show that the host galaxy has a dust-corrected star-formation rate (SFR) of 4.7$\pm$0.2 Msun/yr, with no companion down to 0.22 Msun/yr (5 $σ$) within 240 kpc (30"). Using a high-resolution spectrum (UVES) of the background quasar, which is fortuitously aligned with the galaxy major axis (with an azimuth angle $α$ of only $15^\circ$), we find, in the gas kinematics traced by low-ionization lines, distinct …
Observational constraints on the birth and early evolution of massive black holes (BHs) come from two extreme regimes. At high redshift, quasars signal the rapid growth of billion-solar-mass BHs and indicate that these objects began remarkably heavy and/or accreted mass at rates above the Eddington limit. At low redshift, the smallest nuclear BHs known are found in dwarf galaxies and provide the most concrete limits on the mass of BH seeds. Here we review current observational work in these fields that together are critical for our understanding of the origin of massive BHs in the Universe.
We describe the kinematics of circumgalactic gas near the galactic plane, combining new measurements of galaxy rotation curves and spectroscopy of background quasars. The sightlines pass within 19--93 kpc of the target galaxy and generally detect Mg II absorption. The Mg II Doppler shifts have the same sign as the galactic rotation, so the cold gas co-rotates with the galaxy. Because the absorption spans a broader velocity range than disk rotation can explain, we explore simple models for the circumgalactic kinematics. Gas spiraling inwards (near the disk plane) offers a successful description…
Quasar host galaxies are key for understanding the relation between galaxies and the supermassive black holes (SMBHs) at their centers. We present a study of 191 broad-line quasars and their host galaxies at z < 1, using high signal-to-noise ratio (SNR) spectra produced by the Sloan Digital Sky Survey Reverberation Mapping project. Clear detection of stellar absorption lines allows a reliable decomposition of the observed spectra into nuclear and host components, using spectral models of quasar and stellar radiations as well as emission lines from the interstellar medium. We estimate age, mass…
We obtained optical spectroscopy of close (< 80 kpc) companion objects of a sample of 12 low redshift quasars (z < 0.3 ) selected from the SDSS Stripe82 area and that are in the subsample of 52 QSOs for which both multicolor host galaxies properties and galaxy environment was recently investigated in detail. We found that for 8 out of 12 sources the companion galaxy is associated to the QSO having a difference of radial velocity that is less than 400 km/s. Many of these associated companions exhibit [OII] $λ$3727 Å~ emission lines suggestive of episodes of (recent) star formation possibly indu…
Discovery of Quasar Variability and Early Accretion Disk Signatures at Cosmic Dawn
Massachusetts Institute of Technology（麻省理工学院）；Columbia University（哥伦比亚大学）；Flatiron Institute（平顿研究所）；University of Portsmouth（朴茨茅斯大学）；University of Arizona（亚利桑那大学）；University of Michigan（密歇根大学）
"Green Bean" Galaxies (GBs) are the most [O III]-luminous type-2 active galactic nuclei (AGN) at z~0.3. However, their infrared luminosities reveal AGN in very low activity states, indicating that their gas reservoirs must be ionized by photons from a recent high activity episode - we are observing quasar ionization echoes. We use integral field spectroscopy from the Gemini Multi-Object Spectrograph to analyse the 3D kinematics, ionization state, temperature and density of ionized gas in the GB SDSS J224024.1-092748. We model the emission line spectrum of each spaxel as a superposition of up t…
We present MUSE observations of the field of the quasar Q0152$-$020 whose spectrum shows a Lyman limit system (LLS) at redshift $z_{\rm abs} = 0.38$, with a metallicity Z $\gtrsim 0.06$ Z$_\odot$. The low ionization metal lines associated with the LLS present two narrow distinct absorption components with a velocity separation of 26 km ${\rm s}^{-1}$. We detect six galaxies within 600 km ${\rm s}^{-1}$ from the absorption redshift; their projected distances from the quasar sightline range from 60 to 200 kpc. The optical spectra of five of these galaxies exhibit prominent nebular emission lines…
We present a dynamical analysis of a quasar-host galaxy at $z\simeq 6$ (SDSS J2310+1855) using a high-resolution ALMA observation of the [CII] emission line. The observed rotation curve was fitted with mass models that considered the gravitational contribution of a thick gas disc, a thick star-forming stellar disc, and a central mass concentration, which is likely due to a combination of a spheroidal component (i.e. a stellar bulge) and a supermassive black hole (SMBH). The SMBH mass of $5\times 10^9\ \rm M_{\odot}$, previously measured using the CIV and MgII emission lines, is not sufficient …
Outflows in quasars during the early epochs of galaxy evolution are an important part of the feedback mechanisms potentially affecting the evolution of the host galaxy. However, systematic observations of outflows are only now becoming possible with the advent of sensitive mm telescopes. In this study we use spectral stacking methods to search for faint high velocity outflow signal in a sample of [C II] detected, z ~ 6 quasars. We search for broad emission line signatures from high-velocity outflows for a sample of 26 z ~ 6 quasars observed with ALMA, with a detection of the [C II] line. The o…
The search for Population III (Pop III) stars has fascinated and eluded astrophysicists for decades. One promising place for capturing evidence of their presence must be high-redshift objects; signatures should be recorded in their characteristic chemical abundances. We deduce the Fe and Mg abundances of the broad-line region (BLR) from the intensities of ultraviolet Mg II and Fe II emission lines in the near-infrared spectrum of UKIDSS Large Area Survey (ULAS) J1342+0928 at $z = 7.54$, by advancing our novel flux-to-abundance conversion method developed for $z\sim 1$ quasars. We find that the…
We have determined detailed elemental abundances and stellar ages for a sample of now 38 microlensed dwarf and subgiant stars in the Galactic bulge. Stars with sub-solar metallicities are all old and have enhanced alpha-element abundances -- very similar to what is seen for local thick disk stars. The metal-rich stars on the other hand show a wide variety of stellar ages, ranging from 3-4 Gyr to 12 Gyr, and an average around 7-8 Gyr. The existence of young and metal-rich stars are in conflict with recent photometric studies of the bulge which claim that the bulge only contains old stars.
Photoionization modeling of certain low-ionization broad absorption lines in quasars implies very compact (Delta R~0.01 pc), galaxy-scale (R kpc) absorbers blueshifted by several 1000 km s^-1. While these are likely signatures of quasar outflows, the lifetimes of such compact absorbers are too short for them to be direct ejecta from a nuclear wind. Instead, I argue that the absorbing clouds must be transient and created in situ. Following arguments detailed by Faucher-Giguere, Quataert, & Murray (2011), I show that a model in which the cool absorbers form in radiative shocks arising when a qua…
The quasar PG 1302$-$102 is believed to harbour a supermassive binary black hole (SMBBH) system. Using the available 15 GHz and $2-8$ GHz, multi-epoch Very Long Baseline Array data, we constrain the pc-scale jet properties based on the inferred mean proper motion, including a bulk Lorentz factor $\geq 5.1 \pm 0.8$, jet inclination angle $\leq (11.4 \pm 1.7)$ degrees, projected position angle $= 31.8$ degrees, intrinsic half opening angle $\leq (0.9 \pm 0.1)$ degrees and a mean $2-8$ GHz spectral index of 0.31. A general relativistic helical jet model is presented and applied to predict quasi-p…
We present results from the largest systematic investigation of broad absorption line (BAL) acceleration to date. We use spectra of 140 quasars from three Sloan Digital Sky Survey programs to search for global velocity offsets in BALs over timescales of ~2.5-5.5 years in the quasar rest frame. We carefully select acceleration candidates by requiring monolithic velocity shifts over the entire BAL trough, avoiding BALs with velocity shifts that might be caused by profile variability. The CIV BALs of two quasars show velocity shifts consistent with the expected signatures of BAL acceleration, and…
Broad absorption line quasars are among the objects presenting the fastest outflows. The launching mechanism itself is not completely understood. Models in which they could be launched from the accretion disk, and then curved and accelerated by the effect of the radiation pressure, have been presented. We conducted an extensive observational campaign, from radio to optical band, to collect information about their nature and test the models present in the literature, the main dichotomy being between a young scenario and an orientation one. We found a variety of possible orientations, morphologi…
Many Active Galactic Nuclei (AGN) surveys rely on optical emission line signatures for robust source classification. There are, however, examples of luminous AGN candidates lacking such signatures, including those from the narrow line region, which are expected to be less susceptible to classical nuclear (torus) obscuration. Here, we seek to formalise this subpopulation of AGN with a prototypical candidate, SDSS J075139.06+402810.9. This shows IR colours typical for AGN, an optical spectrum dominated by an early type galaxy continuum,an [OIII] 5007Å limiting flux about two dex below Type 2 qua…
Lomb-Scargle periodograms struggle with non-sinusoidal supermassive BH binary signatures in quasar lightcurves
Columbia University（哥伦比亚大学）；Washington State University（华盛顿州立大学）；Institute of Astrophysics, FORTH（FORTH天体物理研究所）；Institute of Science and Technology Austria (ISTA)（奥地利科学与技术研究所）
Physically motivated AGN emissivity profiles and their effects on quasar microlensing signatures. 1. Multi-epoch accretion disc size inference
IFPU - Institute for Fundamental Physics of the Universe（基础物理宇宙研究所）；SISSA - International School for Advanced Studies（国际高等研究院）；INAF - Osservatorio Astronomico di Trieste（的里雅斯特天文台）；Center for Astrophysics and Cosmology, University of Nova Gorica（新戈里察大学天体物理学与宇宙学中心）
Quasar microlensing offers a unique opportunity to resolve tiny sources in distant active galactic nuclei and study compact object populations in lensing galaxies. We therefore searched for microlensing-induced variability of the gravitationally lensed quasar QSO 2237+0305 (Einstein Cross) using 4374 optical frames taken with the 2.0 m Liverpool Telescope and the 1.5 m Maidanak Telescope. These $gVrRI$ frames over the 2006$-$2019 period were homogeneously processed to generate accurate long-term multi-band light curves of the four quasar images A-D. Through difference light curves, we found st…
Massive Black Holes Seeded by Dark Matter -- Implications for Little Red Dots and Gravitational Wave Signatures
John A. Paulson School of Engineering and Applied Sciences, Harvard University（哈佛大学约翰·A·保尔森工程与应用科学学院）；Kavli Institute for Astrophysics and Space Research, Massachusetts Institute of Technology（麻省理工学院卡弗里天体物理与空间研究所）；Theory Division, Fermilab（费米实验室理论部）；Kavli Institute for Cosmological Physics, University of Chicago（芝加哥大学卡弗里宇宙物理学研究所）；Kavli Institute for Astronomy and Astrophysics, Peking University（北京大学卡弗里天文学与天体物理研究所）
We report a synchronized kinematic shift of CIV and SiIV broad absorption lines (BAL) in a high-ionization, radio-loud, and X-ray bright quasar SDSS-J092345+512710 (at $z_{em} \sim 2.1627$). This quasar shows two broad absorption components (blue component at $v \sim 14,000\ km\ s^{-1}$, and red component at $v \sim 4,000\ km\ s^{-1}$ with respect to the quasars systemic redshift). The absorption profiles of CIV and SiIV BAL of the blue component show decrease in outflow velocity with an average deceleration rate of $-1.62_{-0.05}^{+0.04}\ cm\ s^{-2}$ and $-1.14^{+0.21}_{-0.22}\ cm\ s^{-2}$ ov…
Broad absorption line (BAL) features in quasar spectra reveal an unambiguous signature of energetic outflows from central supermassive black holes, and thus BAL quasars are prime targets for investigating the potential process of luminous quasar feedback on galaxies. We analyzed the rest-UV spectrum of an "overlapping trough" iron low-ionization broad absorption line quasar (FeLoBAL) SDSS J135246.37+423923.5 using the novel spectral synthesis code SimBAL (Leighly et al. 2018) and discovered an extraordinarily fast and energetic BAL outflow. Our analysis revealed outflow velocities reaching $\s…
Observational evidence revealing the main mechanisms that accelerate quasar outflows has proven difficult to obtain, due to the complexity of the absorption features that this gas produces in the spectra of the emission sources. We build 36 composite outflow spectra, covering a large range of outflow and quasar parameters, by stacking broad ($>450\,{\rm km\,s^{-1}}$) absorption line systems in the spectra of SDSS-III/BOSS DR12 quasars. The two lines of the atomic doublet of CIV, with a separation of $\approx 497\,{\rm km\,s^{-1}}$, as well as those of other species appear well resolved in most…
We study the distribution and kinematics of the cool circumgalactic medium (CGM) of emission line galaxies (ELGs) traced by metal absorption lines. Using about 200,000 ELGs from SDSS-IV eBOSS and half a million background quasars from SDSS, we measure the median absorption strength of MgII and FeII lines in quasar spectra for impact parameters ranging from 10 kpc to 1 Mpc. For comparison we measure the same quantity around luminous red galaxies (LRGs). On scales greater than 100 kpc both ELGs and LRGs exhibit similar absorption profiles. However, metal absorption is 5-10 times stronger around …
