arXiv subjects

Marie Wingyee Lau

Publications and source records attributed to Marie Wingyee Lau.

17 recordsLinked to original sources

arXiv2026

Kinematic Stratification in Extremely Red Quasars Revealed by JWST

We analyze the spectra of the central nuclei of extremely red quasars (ERQs) observed as part of the JWST ERS Q3D program. We focus on the complex kinematic structures of the prominent rest-frame optical emission lines. Our modeling allows us to deblend the lines and separate the emission into distinct kinematic components that imply velocity- and density-stratified gas structures on a range of physical scales within the ERQs. Supplementing the JWST data with archival data, we analyze the spectral energy distributions (SEDs) of the ERQs and find they are consistent with a significantly dust-obscured central source with a small amount of relatively-unobscured UV/optical flux that is scattered into our line-of-sight. While the kinematics of the UV and optical emission lines largely agree, the UV lines are dominated by scattered light. In contrast, the optical emission-line ratios indicate a combination of scattered and obscured emission. Our analysis focuses on one ERQ, J0834, because its distinct spectroscopic features allow the emission to be easily decomposed into separate kinematic components.

astro-ph.GA↗

arXiv2026

The Two Component Circumgalactic Medium Emission around z~2 Radio-loud Quasars

We present Ly$α$, He II and C IV observations of 7 redshift ~ 2 radio-loud quasars observed using the Keck Cosmic Web Imager (KCWI) and compare it to observed radio jet emission using archival VLA and ALMA radio observations. We detect 80-120 kpc diameter Ly$α$ and 10-40 kpc He II and C IV emission around the targets. We find the Ly$α$ emission to be brighter in the inner 30 kpc by factors of 2-10 compared to other literature samples. We reproduce the trend for increased total luminosity for a larger area on sky, but find our targets tend to be brighter for a given area when compared to literature observations, even when adjusting for the observational sensitivity. We infer that the He II and C IV is likely powered by quasar photoionization, with the ionizing radiation likely escaping along the radio jet axis which is aligned with the He II and C IV emission. The observations agree with a two component model of the CGM where the inner CGM (< 30 kpc) is directly influenced by the host galaxies, whereas the gas motion in the outer CGM (> 30 kpc) is influenced by gas turbulence and the larger environment around the host galaxies.

astro-ph.GA↗

arXiv2025

JWST IFU observations uncover host galaxy continua in extremely red and obscured quasars

Uncovering bright quasars' host galaxies at cosmic noon is challenging because of the high contrast between the quasar and its host and redshifted light, making them primarily visible in the infrared. We present JWST NIRSpec integral field unit (IFU) observations of six extremely red quasars (ERQs) at $z=2.4-2.9$ and two dust-obscured quasars at lower redshifts. Using image decomposition across the spectral range, we successfully separate quasar and host galaxy continuum emission, model host morphologies, and extract spectra. The ERQs and obscured quasars have compact host galaxies with half-light radii of 1.4$-$2.9 kpc and stellar masses of 10$^{10.6-10.9}$ $M_{\odot}$. Their stellar masses are consistent with the average stellar mass of quasar hosts as expected from abundance matching and clustering analysis. Most of the quasars in our sample exhibit significant spatial offsets (0.4$-$1.3 kpc) between the quasar and host galaxy, potentially caused by post-merger dynamics or non-uniform dust obscuration. The ERQs reside 0.5$-$2 dex above the local black hole-stellar mass relation, similar to other heavily obscured populations such as HotDOGs, optically selected quasars at cosmic noon, and high-redshift SMBH candidates identified with JWST. However, this "over-massive" feature might be attributed to selection bias. Compared to HST-based studies, our JWST measurements reveal more compact host galaxies, smaller Sersic indices, and lower stellar masses, likely because of improved resolution, more accurate modeling, and minimal line contamination. These findings highlight the unique capabilities of JWST IFU in revealing quasar host galaxy properties and potential evolutionary stages of obscured quasars at cosmic noon.

astro-ph.GA↗

arXiv2025

Tracking Outflow using Line-Locking (TOLL). II. Large Line-Locking Web identified in Quasar J151352+085555

Quasar outflows often consist of two clouds with velocity separations matching the doublet spacings of common UV resonance transitions, a phenomenon known as line-locking, which is commonly observed in quasar spectra. Multiple clouds can be locked together through multi-ion doublets, forming 'line-locking web'. In the second paper of the TOLL project, we present discovery of one of the largest 'line-locking web' known to date from the VLT/UVES spectra of QSO J151352+085555. We identify 12 associated narrow absorption line systems through the C IV, N V, Si IV, O VI, and multiple Lyman lines (Ly$α$ to Ly$ε$), and find 10 out of the 12 absorbers are line-locked together by comparing velocity separations between different absorption systems. By conducting photoionization modeling with CLOUDY, we measure the total hydrogen column densities, metallicities, and ionization parameters of these absorbers, which suggests the absorbers likely have sub-solar metallicities. A preliminary statistical analysis demonstrates the shadowed clouds tend to have similar ionization states comparing to the shadowing ones. Identification of one of the largest line-locking webs implies that radiative acceleration plays an important role in sorting out cloud velocities in quasar outflows, and highlights the need for more sophisticated theoretical models to explain its formation and evolution.

astro-ph.GA↗

arXiv2024

[OIII] 5007 emissions in extremely red quasars (ERQs) are compact

``Extremely red quasars'' (ERQs) are a non-radio-selected, intrinsically luminous population of quasars at cosmic noon selected by their extremely red colour from rest-frame UV to mid-IR. ERQs are uniquely associated with exceptionally broad and blueshifted [OIII] 5007 emission reaching speeds >6000 km s^-1. We obtained adaptive optics integral-field spectroscopic observations using Keck/OSIRIS and Gemini/NIFS of a sample of 10 ERQs with bolometric luminosities (10^47.0-10^47.9) erg s^-1 at z ~(2.3-3.0). The goal is to measure the sizes and spatially-resolved kinematics of the [OIII]-emitting regions. We study the surface brightness maps and aperture-extracted spectra and model the point-spread functions. We identify signs of merger activities in the continuum emissions. We identify physically distinct [OIII] kinematic components that are bimodal and respectively trace ERQ-driven outflows of velocity dispersion >250 km s^-1 and dynamically quiescent interstellar media. We find that the ERQ-driven ionized outflows are typically at ~1 kpc scales whereas the quiescent ionized gas extend to a few kpc. Compared to normal quasars the extremely fast ERQ-driven [OIII] outflows tend to be more compact, supporting the notion that ERQs are in a young stage of quasar/galaxy evolution and represent systems with unique physical conditions beyond orientation differences with normal quasar populations. The kinematically quiescent [OIII] emissions in ERQs tend to be spatially-resolved but less extended than in normal quasars, which can be explained by global and patchy dust obscuration. The hint of ionization cones suggests some of the obscuration can be partially explained by a patchy torus.

astro-ph.GA↗

arXiv2023

Accurate Systemic Redshifts and Outflow Speeds for Extremely Red Quasars (ERQs)

Extremely Red Quasars (ERQs) are thought to represent a brief episode of young quasar and galactic evolution characterized by rapid outflows and obscured growth due to dusty environments. We use new redshift measurements from CO and Ly$α$ emission-lines to better constrain outflow velocities from previous line measurements. We present sample of 82 ERQs, and the analysis confirms that ERQs have a higher incidence of large CIV blueshifts, accompanied by large Rest Equivalent Widths (REWs) and smaller line widths than blue quasars. We find that strong blueshifts (>2000 km s$^{-1}$) are present in 12/54 (22.22 per cent) of ERQs with the most robust redshift indicators. At least 4 out of 15 ERQs in the sample also have blueshifts in their H$β$ and low-ionization UV lines ranging from $-$500 to $-$1500 km s$^{-1}$. ERQs with strong CIV blueshifts are substantially offset in CIV REW and Full-Width at Half-Maximum (FWHM) from typical blue quasars in the same velocity range. ERQs have average values of REW = 124 A and FWHM = 5274 km s$^{-1}$, while blue quasars have REW = 24 A and FWHM = 6973 km s$^{-1}$. The extreme nature of the outflows in ERQs might explain some of their other spectral properties, such as the large CIV REWs and peculiar wingless profiles owing to more extended broad-line regions participating in outflows. The physical reasons for the extreme outflow properties of ERQs are unclear; however, larger Eddington ratios and/or softer ionizing spectra incident on the outflow gas cannot be ruled out.

astro-ph.GA↗

arXiv2023

Compact and Quiescent Circumgalactic Medium and Ly$α$ Halos around Extremely Red Quasars (ERQs)

Red quasars may represent a young stage of galaxy evolution that provide important feedback to their host galaxies. We are studying a population of extremely red quasars (ERQs) with exceptionally fast and powerful outflows, at median redshift $z$ = 2.6. We present Keck/KCWI integral field spectra of 11 ERQs, which have a median color $i-W3$ = 5.9~mag, median $\left\langle L_{\text{bol}} \right\rangle$ $\approx$ 5 $\times$ $10^{47}$ erg s$^{-1}$, Ly$α$ halo luminosity $\left\langle L_{\text{halo}} \right\rangle$ $=$ 5 $\times$ $10^{43}$ erg s$^{-1}$, and maximum linear size $>128$ kpc. The ERQ halos are generally similar to those of blue quasars, following known trends with $L_{\text{bol}}$ in halo properties. ERQs have halo symmetries similar to Type-I blue quasars, suggesting Type-I spatial orientations. ERQ $\left\langle L_{\text{halo}} \right\rangle$ is $\sim$2 dex below blue quasars, which is marginal due to scatter, but consistent with obscuration lowering photon escape fractions. ERQ halos tend to have more compact and circularly symmetric inner regions than blue quasars, with median exponential scale lengths of $\sim$9 kpc, compared to $\sim$16 kpc for blue quasars. When we include the central regions not available in blue quasar studies (due to PSF problems), the true median ERQ halo scale length is just $\sim$6 kpc. ERQ halos are also kinematically quiet, with median velocity dispersion 293 km s$^{-1}$, consistent with expected virial speeds. Overall we find no evidence for feedback on circumgalactic scales, and the current episode of quasar activity, perhaps due to long outflow travel times, has not been around long enough to affect the circumgalactic medium. We confirm the narrow Ly$α$ emission spikes found in ERQ aperture spectra are halo features, and are useful for systemic redshifts and measuring outflow speeds in other features.

astro-ph.GA↗

arXiv2022

Probing the Inner Circumgalactic Medium and Quasar Illumination around the Reddest `Extremely Red Quasar' (ERQ)

Dusty quasars might be in a young stage of galaxy evolution with prominent quasar feedback. A recently discovered population of luminous, extremely red quasars at $z\sim$~2--4 has extreme spectral properties related to exceptionally powerful quasar-driven outflows. We present Keck/KCWI observations of the reddest known ERQ, at $z=$\,2.3184, with extremely fast [\ion{O}{III}]~$λ$5007 outflow at $\sim$6000~km~s$^{-1}$. The Ly$α$ halo spans $\sim$100~kpc. The halo is kinematically quiet, with velocity dispersion $\sim$300~km~s$^{-1}$ and no broadening above the dark matter circular velocity down to the spatial resolution $\sim$6~kpc from the quasar. We detect spatially-resolved \ion{He}{II}~$λ$1640 and \ion{C}{IV}~$λ$1549 emissions with kinematics similar to the Ly$α$ halo and a narrow component in the [\ion{O}{III}]~$λ$5007. Quasar reddening acts as a coronagraph allowing views of the innermost halo. A narrow Ly$α$ spike in the quasar spectrum is inner halo emission, confirming the broad \ion{C}{IV}~$λ$1549 in the unresolved quasar is blueshifted by $2240$~km~s$^{-1}$ relative to the halo frame. We propose the inner halo is dominated by moderate-speed outflow driven in the past and the outer halo dominated by inflow. The high central concentration of the halo and the symmetric morphology of the inner region are consistent with the ERQ being in earlier evolutionary stage than blue quasars. The \ion{He}{II}~$λ$1640/Ly$α$ ratio of the inner halo and the asymmetry level of the overall halo are dissimilar to Type~II quasars, suggesting unique physical conditions for this ERQ that are beyond orientation differences from other quasar populations. We find no evidence of mechanical quasar feedback in the Ly$α$-emitting halo.

astro-ph.GA↗

arXiv2021

A Long Stream of Metal-Poor Cool Gas around a Massive Starburst Galaxy at z = 2.67

We present the first detailed dissection of the circumgalactic medium (CGM) of massive starburst galaxies at z > 2. Our target is a submillimeter galaxy (SMG) at z = 2.674 that has a star formation rate of 1200 $M_\odot$/yr and a molecular gas reservoir of $1.3\times10^{11} M_\odot$. We characterize its CGM with two background QSOs at impact parameters of 93 kpc and 176 kpc. We detect strong HI and metal-line absorption near the redshift of the SMG towards both QSOs, each consisting of three main subsystems spanning over 1500 km/s. The absorbers show remarkable kinematic and metallicity coherence across a separation of 86 kpc. In particular, the cool gas in the CGM of the SMG exhibits high HI column densities ($\log N_{\rm HI}/{\rm cm}^{-2} = 20.2, 18.6$), low metallicities ([M/H] $\approx$ -2.0), and similar radial velocities ($\approx$ -300 km/s). While the HI column densities match previous results on the CGM around QSOs at z > 2, the metallicities are lower by more than an order of magnitude, making it an outlier in the line width$-$metallicity relation of damped Ly$α$ absorbers. The large physical extent, the velocity coherence, the high surface density, and the low metallicity are all consistent with the cool, inflowing, and near-pristine gas streams predicted to penetrate hot massive halos at z > 1.5. We estimate a total gas accretion rate of ~100 $M_\odot$/yr from three such streams, which falls short of the star formation rate but is consistent with simulations. At this rate, it takes about a gigayear to acquire the molecular gas reservoir of the central starburst.

astro-ph.GA↗

arXiv2018

Quasars probing quasars X: The quasar pair spectral database

The rare close projection of two quasars on the sky provides the opportunity to study the host galaxy environment of a foreground quasar in absorption against the continuum emission of a background quasar. For over a decade the "Quasars probing quasars" series has utilized this technique to further the understanding of galaxy formation and evolution in the presence of a quasar at z>2, resolving scales as small as a galactic disc and from bound gas in the circumgalactic medium to the diffuse environs of intergalactic space. Presented here, is the public release of the quasar pair spectral database utilized in these studies. In addition to projected pairs at z>2, the database also includes quasar pair members at z<2, gravitational lens candidates and quasars closely separated in redshift that are useful for small-scale clustering studies. In total the database catalogs 5627 distinct objects, with 4083 lying within 5' of at least one other source. A spectral library contains 3582 optical and near-infrared spectra for 3028 of the cataloged sources. As well as reporting on 54 newly discovered quasar pairs, we outline the key contributions made by this series over the last ten years, summarize the imaging and spectroscopic data used for target selection, discuss the target selection methodologies, describe the database content and explore some avenues for future work. Full documentation for the spectral database, including download instructions, are supplied at the following URL http://specdb.readthedocs.io/en/latest/

astro-ph.GA↗

arXiv2018

Quasars Probing Quasars IX. The Kinematics of the Circumgalactic Medium Surrounding z ~ 2 Quasars

We examine the kinematics of the gas in the environments of galaxies hosting quasars at $z\sim2$. We employ 148 projected quasar pairs to study the circumgalactic gas of the foreground quasars in absorption. The sample selects foreground quasars with precise redshift measurements, using emission-lines with precision $\lesssim300\,{\rm km\,s^{-1}}$ and average offsets from the systemic redshift $\lesssim|100\,{\rm km\,s^{-1}}|$. We stack the background quasar spectra at the foreground quasar's systemic redshift to study the mean absorption in \ion{C}{2}, \ion{C}{4}, and \ion{Mg}{2}. We find that the mean absorptions exhibit large velocity widths $σ_v\approx300\,{\rm km\,s^{-1}}$. Further, the mean absorptions appear to be asymmetric about the systemic redshifts. The mean absorption centroids exhibit small redshift relative to the systemic $δv\approx+200\,{\rm km\,s^{-1}}$, with large intrinsic scatter in the centroid velocities of the individual absorption systems. We find the observed widths are consistent with gas in gravitational motion and Hubble flow. However, while the observation of large widths alone does not require galactic-scale outflows, the observed offsets suggest that the gas is on average outflowing from the galaxy. The observed offsets also suggest that the ionizing radiation from the foreground quasars is anisotropic and/or intermittent.

astro-ph.GA↗

arXiv2017

Gaia17biu/SN 2017egm in NGC 3191: The closest hydrogen-poor superluminous supernova to date is in a "normal", massive, metal-rich spiral galaxy

Hydrogen-poor superluminous supernovae (SLSNe-I) have been predominantly found in low-metallicity, star-forming dwarf galaxies. Here we identify Gaia17biu/SN 2017egm as an SLSN-I occurring in a "normal" spiral galaxy (NGC 3191) in terms of stellar mass (several times 10^10 M_sun) and metallicity (roughly Solar). At redshift z=0.031, Gaia17biu is also the lowest redshift SLSN-I to date, and the absence of a larger population of SLSNe-I in dwarf galaxies of similar redshift suggests that metallicity is likely less important to the production of SLSNe-I than previously believed. With the smallest distance and highest apparent brightness for an SLSN-I, we are able to study Gaia17biu in unprecedented detail. Its pre-peak near-ultraviolet to optical color is similar to that of Gaia16apd and among the bluest observed for an SLSN-I while its peak luminosity (M_g = -21 mag) is substantially lower than Gaia16apd. Thanks to the high signal-to-noise ratios of our spectra, we identify several new spectroscopic features that may help to probe the properties of these enigmatic explosions. We detect polarization at the ~0.5% level that is not strongly dependent on wavelength, suggesting a modest, global departure from spherical symmetry. In addition, we put the tightest upper limit yet on the radio luminosity of an SLSN-I with <5.4x10^26 erg/s/Hz (at 10 GHz), which is almost a factor of 40 better than previous upper limits and one of the few measured at an early stage in the evolution of an SLSN-I. This limit largely rules out an association of this SLSNe-I with known populations of gamma-ray burst (GRB) like central engines.

astro-ph.HE↗

arXiv2016

Quasars Probing Quasars VIII. The Physical Properties of the Cool Circumgalactic Medium Surrounding z ~ 2-3 Massive Galaxies Hosting Quasars

We characterize the physical properties of the cool T ~10^4 K circumgalactic medium surrounding z ~2-3 quasar host galaxies, which are predicted to evolve into present day massive ellipticals. Using a statistical sample of 14 quasar pairs with projected separation < 300 kpc and high dispersion, high S/N spectra, we find extreme kinematics with low metal ion lines typically spanning ~ 500 km/s, exceeding any previously studied galactic population. The CGM is significantly enriched, even beyond the virial radius, with a median metallicity [M/H] ~ -0.6. The alpha/Fe abundance ratio is enhanced, suggesting that halo gas is primarily enriched by core-collapse supernovae. The projected cool gas mass within the virial radius is estimated to be 1.9*10^11 M_sun (R_\perp/160 kpc)^2, accounting for ~ 1/3 of the galaxy halo baryonic budget. The ionization state of CGM gas increases with projected distance from the foreground quasars, contrary to expectation if the quasar dominates the ionizing radiation flux. However, we also found peculiarities not exhibited in the CGM of other galaxy populations. In one absorption system, we may be detecting unresolved fluorescent Ly-alpha emission, and another system shows strong NV lines. Taken together these anomalies suggest that transverse sightlines are at least in some cases possibly illuminated. We also discovered a peculiar case where detection of the CII* fine structure line implies an electron density > 100 cm^-3 and subparsec scale gas clumps.

astro-ph.GA↗

arXiv2015

MApping the Most Massive Overdensities Through Hydrogen (MAMMOTH) I: Methodology

Modern cosmology predicts that a galaxy overdensity is associated to a large reservoir of the intergalactic gas, which can be traced by the Ly$α$ forest absorption. We have undertaken a systematic study of the relation between Coherently Strong intergalactic Ly$α$ Absorption systems (CoSLAs), which have highest optical depth ($τ$) in $τ$ distribution, and mass overdensities on the scales of $\sim$ 10 - 20 $h^{-1}$ comoving Mpc. On such large scales, our cosmological simulations show a strong correlation between the effective optical depth ($τ_{\rm{eff}}$) of the CoSLAs and the 3-D mass overdensities. In moderate signal-to-noise spectra, however, the profiles of CoSLAs can be confused with high column density absorbers. For $z>2.6$, where the corresponding Ly$β$ is redshifted to the optical, we have developed the technique to differentiate between these two alternatives. We have applied this technique to SDSS-III quasar survey at $z = 2.6$ - 3.3, and we present a sample of five CoSLA candidates with $τ_{\rm{eff}}$ on 15 $h^{-1}$ Mpc greater than $4.5\times$ the mean optical depth. At lower redshifts of $z < 2.6$, where the background quasar density is higher, the overdensity can be traced by intergalactic absorption groups using multiple sight lines. Our overdensity searches fully utilize the current and next generation of Ly$α$ forest surveys which cover a survey volume of $> (1\ h^{-1}$ Gpc)$^3$. In addition, systems traced by CoSLAs will build a uniform sample of the most massive overdensities at $z > 2$ to constrain the models of structure formation, and offer a unique laboratory to study the interactions between galaxy overdensities and the intergalactic medium.

astro-ph.GA↗

arXiv2014

Dissecting the Gaseous Halos of z~2 Damped Ly$α$ Systems with Close Quasar Pairs

We use spectroscopy of close pairs of quasars to study diffuse gas in the circumgalactic medium (CGM) surrounding a sample of 40 Damped Lya systems (DLAs). The primary sightline in each quasar pair probes an intervening DLA in the redshift range 1.6 < z_DLA < 3.6, such that the second quasar sightline then probes Lya, CII, SiII, and CIV absorption in the CGM transverse to the DLA to projected distances $R_{\perp} < 300$ kpc. Analysis of the Lya profiles in these CGM sightlines constrains the covering fraction (f_C) of optically thick HI (having column density N_HI > 10^17.2 cm^-2) to be greater than ~30% within $R_{\perp} < 200$ kpc of DLAs. Strong SiII 1526 absorption with equivalent width W_1526 > 0.2 Ang occurs with an incidence f_C (W_1526 > 0.2 Ang) = 20(+12/-8)% within $R_{\perp}<100$ kpc, indicating that low-ionization metal absorption associated with DLAs probes material at a physical distance R_3D < 30 kpc. However, we find that strong CIV 1548 absorption is ubiquitous in these environments (f_C (W_1548 > 0.2 Ang) = 57(+12/-13)% within $R_{\perp} < 100$ kpc), and in addition exhibits a high degree of kinematic coherence on scales up to ~175 kpc. We infer that this high-ionization material arises predominantly in large, quiescent structures extending beyond the scale of the DLA host dark matter halos rather than in ongoing galactic winds. The Lya equivalent width in the DLA-CGM is anticorrelated with $R_{\perp}$ at >98% confidence, suggesting that DLAs arise close to the centers of their host halos rather than on their outskirts. Finally, the average Lya, CII and CIV equivalent widths are consistent with those measured around z~2 Lyman Break Galaxies. Assuming that DLAs trace a galaxy population with lower masses and luminosities, this finding implies that the absorption strength of cool circumgalactic material has a weak dependence on dark matter halo mass for M_h < 10^12 M_sun.

astro-ph.GA↗

arXiv2014

Quasars Probing Quasars VII. The Pinnacle of the Cool Circumgalactic Medium Surrounds Massive z~2 Galaxies

We survey the incidence and absorption strength of the metal-line transitions CII 1334 and CIV from the circumgalactic medium (CGM) surrounding z~2 quasars, which act as signposts for massive dark matter halos M_halo~10^12.5 Msun. On scales of the virial radius (Mvir~160kpc), we measure a high covering fraction fC=0.73+/-0.10 to strong CII absorption (rest equivalent width W1334>0.2A), implying a massive reservoir of cool (T~10^4K) metal enriched gas. We conservatively estimate a metal mass exceeding 10^8 Msun. We propose these metals trace enrichment of the incipient intragroup/intracluster medium that these halos eventually inhabit. This cool CGM around quasars is the pinnacle amongst galaxies observed at all epochs, as regards covering fraction and average equivalent width of HI Lya and low-ion metal absorption. We argue that the properties of this cool CGM primarily reflect the halo mass, and that other factors such as feedback, star-formation rate, and accretion from the intergalactic medium are secondary. We further estimate, that the CGM of massive, z~2 galaxies accounts for the majority of strong MgII absorption along random quasar sightlines. Lastly, we detect an excess of strong CIV absorption (W1548>0.3A) over random incidence to 1Mpc physical impact parameter and measure the quasar-CIV cross-correlation function: xi(r)=(r/r0)^-g with r0 = 7.5Mpc and g=1.7. Consistent with previous work on larger scales, we infer that this highly ionized CIV gas traces massive (10^12 Msun) halos.

astro-ph.GA↗

arXiv2013

Quasars Probing Quasars VI. Excess HI Absorption Within One Proper Mpc of z~2 Quasars

With close pairs of quasars at different redshifts, a background quasar sightline can be used to study a foreground quasar's environment in absorption. We use a sample of 650 projected quasar pairs to study the HI Lya absorption transverse to luminous, z~2 quasars at proper separations of 30kpc < R < 1Mpc. In contrast to measurements along the line-of-sight, regions transverse to quasars exhibit enhanced HI Lya absorption and a larger variance than the ambient intergalactic medium, with increasing absorption and variance toward smaller scales. Analysis of composite spectra reveals excess absorption characterized by a Lya equivalent width profile W = 2.3A (R/100kpc)^-0.46. We also observe a high (~60%) covering factor of strong, optically thick HI absorbers (HI column log NHI > 17.3) at separations R<200kpc, which decreases to ~20% at R~1Mpc, but still represents a significant excess over the cosmic average. This excess of optically thick absorption can be described by a quasar-absorber cross-correlation function xi_QA(r) = (r/r_0)^gamma with a large correlation length r_0 = 12.5+2.7-1.4 Mpc/h (comoving) and gamma = 1.68+0.14-0.30. The HI absorption measured around quasars exceeds that of any previously studied population, consistent with quasars being hosted by massive dark matter halos Mhalo~10^12.5 Msun at z~2.5. The environments of these massive halos are highly biased towards producing optically thick gas, and may even dominate the cosmic abundance of Lyman limit systems and hence the intergalactic opacity to ionizing photons at z~2.5. The anisotropic absorption around quasars implies the transverse direction is much less likely to be illuminated by ionizing radiation than the line-of-sight, which we interpret in terms of the same obscuration effects frequently invoked in unified models of active galactic nuclei.

astro-ph.CO↗