Quasar Environments Research Articles

The rich galactic environment of a H2-absorption-selected quasar

We present the first Very Large Telescope (VLT) Multi Unit Spectroscopic Explorer (MUSE) observations of a quasar featuring a proximate molecular absorption system, SDSS J125917.31+030922.5. The proximate damped Lyα absorption acts as a natural coronagraph, removing the quasar emission over ∼40 Å in wavelength, and allows us to detect extended Lyα emission without the necessity of subtracting the quasar emission. This natural coronagraph permits the investigation of the quasar environment down to its inner regions (r < 20 kpc), where galaxy interactions or feedback processes should have the most noticeable effects. Our observations reveal a dense environment, with a highly asymmetric Lyα emission within 2″ (∼15 kpc), possibly shaped by a companion galaxy, and a southern extension of the nebulae to about 50 kpc, with rotation-like kinematic signature. The width of the Lyα emission is broadest closer to the quasar, indicating perturbed kinematics as expected if interactions and significant gas flows are present. The foreground absorbing system itself is redshifted by ≈400 km/s relative to the background quasar, and therefore is likely arising from gas moving toward the quasar. Finally two additional Lyα emitters are detected with > 10σ significance at 96 and 223 kpc from the quasar, making this field overdense relative to other similar observations of quasars at z ∼ 3. Our results support the hypothesis that quasars with proximate neutral and molecular absorption trace rich environments where galaxy interactions are at play and motivates further studies of H2-selected quasars to shed light on feeding and feedback processes.

Robustness of direct measurements of the mean free path of ionizing photons in the epoch of reionization

ABSTRACT Measurements of the mean free path of Lyman-continuum photons in the intergalactic medium during the epoch of reionization can help constrain the nature of the sources as well as sinks of hydrogen-ionizing radiation. A recent approach to this measurement has been to utilize composite spectra of multiple quasars at $z\sim 6$, and infer the mean free path after correcting the spectra for the presence of quasar proximity zones. This has revealed not only a steep drop in the mean free path from $z=5$ to $z=6$, but also potentially a mild tension with reionization simulations. We critically examine such direct measurements of the mean free path for biases due to quasar environment, incomplete reionization, and quasar proximity zones. Using cosmological radiative transfer simulations of reionization combined with one-dimensional radiative transfer calculations of quasar proximity zones, we find that the bias in the mean free path due to overdensities around quasars is minimal at $z\sim 6$. Patchiness of reionization at this redshift also does not affect the measurements significantly. Fitting our model to the data results in a mean free path of $\lambda _{\mathrm{mfp}}=1.49^{+0.47}_{-0.52}$ pMpc at $z=6$, which is consistent with the recent measurements in the literature, indicating robustness with respect to the modelling of quasar proximity zones. We also compare various ways in which the mean free path has been defined in simulations before the end of reionization. Overall, our finding is that recent measurements of the mean free path appear to be robust relative to several sources of potential bias.

QUAS(AI)R: A Novel Machine Learning Algorithm to Predict X-ray Brightness in Active Galactic Nuclei

Active Galactic Nuclei (AGNs) are a compact region at the center of galaxies that emit more energy than the rest of the galaxy itself. They emit light across the electromagnetic spectrum, from radio waves to optical light to high-energy X-rays. AGNs indicate the existence of highly energetic phenomena in the nucleus of the galaxy. Although AGNs were identified 60 years ago, our knowledge about their physical properties is limited. Quasars, a subtype of AGNs, provide some of the most intense forms of X-rays, which are among the most energetic light known. Furthering our understanding of X-rays in the dynamic environments of quasars will add to our understanding of how to benefit from their use on Earth. In my project, I study the X-ray brightness in quasars to develop six types of regression-based machine learning models for the X-ray brightness predictions. These six models were Stochastic Gradient Descent (SGD), Random Forest, Ridge, Lasso, Bayesian and the baseline linear regression model, built on the scikit-learn Python package. The training/testing split on the MILLIQUAS dataset was 80/20 percent, and each model was tuned on model-specific hyperparameters. Benchmarked with the normalized mean absolute error (NMAE), the top three performing models were the Bayesian (0.022%), Ridge (0.180%), and Lasso (0.183%), with the baseline NMAE at 0.284%. With this, we can learn more about the evolution of galaxies in the early Universe and understand how these dynamic environments came to be.

The effect of reionization on direct measurements of the mean free path

ABSTRACT Recent measurements of the ionizing photon mean free path (MFP) based on composite quasar spectra may point to reionization ending at z < 6. These measurements are challenging because they rely on assumptions about the proximity zones of the quasars. For example, some quasars might have been close to neutral patches where reionization was still ongoing (‘neutral islands’), and it is unclear how they would affect the measurements. We address this question with mock MFP measurements from radiative transfer simulations. We find that, even in the presence of neutral islands, our mock MFP measurements agree to within $30~{{\ \rm per\ cent}}$ with the true spatially averaged MFP in our simulations, which includes opacity from both the ionized medium and the islands. The inferred MFP is sensitive at the $\lt ~50~{{\ \rm per\ cent}}$ level to assumptions about quasar environments and lifetimes for realistic models. We demonstrate that future analyses with improved data may require explicitly modelling the effects of neutral islands on the composite spectra, and we outline a method for doing this. Lastly, we quantify the effects of neutral islands on Lyman-series transmission, which has been modelled with optically thin simulations in previous MFP analyses. Neutral islands can suppress transmission at λrest < 912 Å significantly, up to a factor of 2 for zqso = 6 in a plausible reionization scenario, owing to absorption by many closely spaced lines as quasar light redshifts into resonance. However, the suppression is almost entirely degenerate with the spectrum normalization and thus does not significantly bias the inferred MFP.

The Cosmic Ultraviolet Baryon Survey (CUBS). VIII. Group Environment of the Most Luminous Quasars at z ≈ 1

We investigate the group-scale environment of 15 luminous quasars (luminosity L 3000 > 1046 erg s−1) from the Cosmic Ultraviolet Baryon Survey (CUBS) at redshift z ≈ 1. Using the Multi Unit Spectroscopic Explorer integral field spectrograph on the Very Large Telescope, we conduct a deep galaxy redshift survey in the CUBS quasar fields to identify group members and measure the physical properties of individual galaxies and galaxy groups. We find that the CUBS quasars reside in diverse environments. The majority (11 out of 15) of the CUBS quasars reside in overdense environments with typical halo masses exceeding 1013 M ⊙, while the remaining quasars reside in moderate-size galaxy groups. No correlation is observed between overdensity and redshift, black hole (BH) mass, or luminosity. Radio-loud quasars (5 out of 15 CUBS quasars) are more likely to be in overdense environments than their radio-quiet counterparts in the sample, consistent with the mean trends from previous statistical observations and clustering analyses. Nonetheless, we also observe radio-loud quasars in moderate groups and radio-quiet quasars in overdense environments, indicating a large scatter in the connection between radio properties and environment. We find that the most UV luminous quasars might be outliers in the stellar mass-to-halo mass relations or may represent departures from the standard single-epoch BH relations.

SCUBA-2 High Redshift Bright Quasar Survey. II. The Environment of z ∼ 6 Quasars at Submillimeter Band

The formation of the first supermassive black holes is expected to have occurred in some most pronounced matter and galaxy overdensities in the early universe. We have conducted a submillimeter wavelength continuum survey of 54 z ∼ 6 quasars using the Submillimeter Common-User Bolometre Array-2 on the James Clerk Maxwell Telescope to study the environments around z ∼ 6 quasars. We identified 170 submillimeter galaxies (SMGs) with above 3.5σ detections in 450 or 850 μm maps. Their far-IR luminosities are (2.2–6.4) × 1012 L ⊙, and their star formation rates are ∼400–1200 M ⊙ yr−1. We also calculated the SMGs’ differential and cumulative number counts in a combined area of ∼620 arcmin2. To a 4σ detection (at ∼5.5 mJy), SMGs’ overdensity is (±0.19), exceeding the blank-field source counts by a factor of 1.68. We find that 13/54 quasars show overdensities (at ∼5.5 mJy) of δ SMG ∼ 1.5–5.4. The combined area of these 13 quasars exceeds the blank-field counts with the overdensity to 5.5 mJy of δ SMG ∼ (±0.25) in the regions of ∼150 arcmin2. However, the excess is insignificant on the bright end (e.g., 7.5 mJy). We also compare results with previous environmental studies of Lyα emitters and Lyman break galaxies on a similar scale. Our survey presents the first systematic study of the environment of quasars at z ∼ 6. The newly discovered SMGs provide essential candidates for follow-up spectroscopic observations to test whether they reside in the same large-scale structures as the quasars and search for protoclusters at an early epoch.

JCMT/SCUBA-2 uncovers an excess of 850 μm counts on megaparsec scales around high-redshift quasars

We conducted a systematic survey of the environment of high-redshift quasars at submillimeter wavelengths to unveil and characterize the surrounding distribution of dusty submillimeter galaxies (SMGs). We took sensitive observations with the SCUBA-2 instrument on the James Clerk Maxwell Telescope for 3 enormous Lyman-alpha nebulae (ELANe) and 17 quasar fields in the redshift range 2 < z < 4.2 selected from recent Lyman alpha (Lyα) surveys. These observations uncovered 523 and 101 sources at 850 μm and 450 μm, respectively, with signal-to-noise ratios (S/N) > 4 or detected in both bands at S/N > 3. We ran self-consistent Monte Carlo simulations to construct 850 μm number counts and unveil an excess of sources in 75% of the targeted fields. Overall, regions around ELANe and quasars are overabundant with respect to blank fields by a factor of 3.4 ± 0.4 and 2.5 ± 0.2, respectively (weighted averages). Therefore, the excess of submillimeter sources is likely part of the megaparsec-scale environment around these systems. By combining all fields and repeating the count analysis in radial apertures, we find (at high significance, ≳5σ) a decrease in the overdensity factor from > 3 within ∼2 cMpc to ∼2 in the annulus at the edge of the surveyed field (∼10 cMpc), which suggests that the physical extent of the overdensities is larger than our maps. We computed preferred directions for the overdensities of SMGs from the positions of the sources and used them to orient and create stacked maps of source densities for the quasars’ environment. This stacking unveils an elongated structure reminiscent of a large-scale filament with a scale width of ≈3 cMpc. Finally, the directions of the overdensities are roughly aligned with the major axis of the Lyα nebulae, suggesting that the latter trace, on scales of hundreds of kiloparsecs, the central regions of the projected large-scale structure described by the SMGs on megaparsec scales. Confirming member associations of the SMGs is required to further characterize their spatial and kinematic distribution around ELANe and quasars.

The feedback of quasars on their galactic environment

ABSTRACTQuasar outflows might either quench (negative) or enhance (positive feedback) star formation in galaxies located in the quasar environment. The possible outcome depend on 4 parameters: The quasar (σ) and satellite (σ*) halo velocity dispersion, their relative distance, d, and satellite disc radius, rd. We find that: (i) small satellites with $\sigma _* \lt 164\ \sigma _{200}^{2/3}\, \rm km\ s^{-1}$ have their star formation quenched; (ii) in larger satellites, star formation, and hence UV/far-infrared (FIR) luminosity, is instead boosted by >80 per cent in a burst with typical duration of 5–10 Myr, if the following positive feedback criterion is met: d/rd < 15(Q/η)1/2σ200, where Q ≈ 1 is the satellite disc Toomre parameter; the disruption parameter (see equation 17) must be η > 1 to prevent complete satellite gas removal. We compare our predictions with ALMA data finding that observed satellites of z ≃ 6 QSOs on average form stars at a 3 × higher rate with respect to field galaxies at the same redshift. Further tests of the model are suggested.

The 2175 Å bump features in FeLoBAL quasars: One indicator of MW-like dust in the nuclear region of quasars

To investigate the properties of dust in the nuclear region of quasars, we explored the extinction curves of the iron low-ionisation broad absorption line (FeLoBAL) quasar SDSS J163004.29+311957.6 and its two analogues. The parametrised extinction curves indicated the Milky Way-like 2175 Å bump features in underlying extinction, which are similar to those seen in the Local Group and in a subset of high-redshift star-forming galaxies. Compared to the bump features in the Large Magellanic Cloud (LMC), the detections in this work are much closer to those in the Milky Way (MW). These bump features, as well as those in the high- and low-ionisation broad absorption line (BAL) quasars with 2175 Å bumps, are probably the counterpart of the 2175 Å bump features in the quasar environment. This type of dust grain is generally small, easily disrupted by high-energy photons, and has difficulty surviving in the radiation field of the active galactic nucleus. However, due to the presence of absorption-line outflows, the 2175 Å bump feature in quasars, which should be rare, is seen many times in BAL quasars. The shielding effect of outflow clouds allows the MW-like dust grains to be assembled or extends the survival period in the quasar nuclear region. The process and physical and chemical conditions deserve further observational study and investigation.

Exploratory Study of the Transverse Proximity Effect around BAL Quasars

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.

ALMA Reveals a Large Overdensity and Strong Clustering of Galaxies in Quasar Environments at z ∼ 4

Abstract We present an Atacama Large Millimeter/submillimeter Array (ALMA) survey of CO(4–3) line emitting galaxies in 17 quasar fields at z ∼ 4 aimed at performing the first systematic search of dusty galaxies in high-z quasar environments. Our blind search of galaxies around the quasars results in five CO emitters with S/N ≥ 5.6 within a projected radius of R ≲ 1.5 h −1 cMpc and a velocity range of δv = ±1000 km s−1 around the quasar. In blank fields, we expect to detect only 0.28 CO emitters within the same volume, implying a total overdensity of 17.6 − 7.6 + 11.9 in our fields, and indicating that quasars trace massive structures in the early universe. We quantify this overdensity by measuring the small-scale clustering of CO emitters around quasars, resulting in a cross-correlation length of r 0 , QG = 8.37 − 2.04 + 2.42 h − 1 cMpc, assuming a fixed slope γ = 1.8. This contradicts the reported mild overdensities (x1.4) of Lyα emitters (LAEs) in the same fields at scales of R ≲ 7 h −1 cMpc, which are well described by a cross-correlation length 3.0 − 1.4 + 1.5 times lower than that measured for CO emitters. We discuss some possibilities to explain this discrepancy, including low star formation efficiency, and excess of dust in galaxies around quasars. Finally, we constrain, for the first time, the clustering of CO emitters at z ∼ 4, finding an autocorrelation length of r 0,CO = 3.14 ±1.71 h −1 cMpc (with γ = 1.8). Our work, together with the previous study of LAEs around quasars, traces simultaneously the clustering properties of both optical and dusty galaxy populations in quasars fields, stressing the importance of multiwavelength studies, and highlighting important questions about galaxy properties in high-z dense environments.

The Highly Self-absorbed Blazar PKS 1351-018

Abstract PKS 1351-018 at a redshift of z = 3.71 is one of the most luminous, steady synchrotron sources with a luminosity &gt;1047 erg s−1. The synchrotron luminosity does not seem to have varied by more than ∼25% over 35 yr. In order to appreciate this remarkable behavior, if it were at z = 0.5, it would have a flux density at 15 GHz in a range of 110–137 Jy over 11 yr. In spite of this steady behavior, two strong γ-ray flares ≲1049 erg s−1 were detected in 2011 and 2016. There is a blazar-like behavior coexisting with the steady behavior. This study is aimed at elucidating the dual nature of this source. We find that the radio source is extremely compact with a bright core and a steep spectrum secondary component, 12 mas away, that appears to be constant in position and flux density in six epochs from 1995–2018. We estimate that a jet with a time averaged power of (5.2 ± 3.2) × 1045 erg s−1 terminates in this lobe, which is advancing ≳0.9c at a deprojected distance of 1–3 kpc from the central engine. This is the rare case of a young (∼6000 yr), very powerful radio source that is viewed a few degrees from the jet axis. We find evidence of a high velocity (4000 km s−1), high ionization wind emanating from a luminous quasar. The young radio jet appears to experience modest bending as it navigates through the intense quasar environment.

The Diversity of Environments around Luminous Quasars at Redshift z ∼ 6

Abstract Significant clustering around the rarest luminous quasars is a feature predicted by dark matter theory combined with number density matching arguments. However, this expectation is not reflected by observations of quasars residing in a diverse range of environments. Here we assess the tension in the diverse clustering of visible i-band dropout galaxies around luminous z ∼ 6 quasars. Our approach uses a simple empirical method to derive the median luminosity–to–halo mass relation, L c (M h ), for both quasars and galaxies under the assumption of lognormal luminosity scatter, Σ Q and Σ G . We show that higher Σ Q reduces the average halo mass hosting a quasar of a given luminosity, thus introducing at least a partial reversion to the mean in the number count distribution of nearby Lyman-break galaxies. We generate a large sample of mock Hubble Space Telescope fields of view centered across rare z ∼ 6 quasars by resampling pencil beams traced through the dark matter component of the BlueTides cosmological simulation. We find that diverse quasar environments are expected for Σ Q &gt; 0.4, consistent with numerous observations and theoretical studies. However, we note that the average number of galaxies around the central quasar is primarily driven by galaxy evolutionary processes in neighboring halos, as embodied by our parameter Σ G , instead of a difference in the large-scale structure around the central quasar host, embodied by Σ Q . We conclude that models with Σ G &gt; 0.3 are consistent with current observational constraints on high-z quasars, and that such a value is comparable to the scatter estimated from hydrodynamical simulations of galaxy formation.

The dust attenuation law in z ∼ 6 quasars

ABSTRACT We investigate the attenuation law in z ∼ 6 quasars by combining cosmological zoom-in hydrodynamical simulations of quasar host galaxies, with multifrequency radiative transfer calculations. We consider several dust models differing in terms of grain-size distributions, dust mass, and chemical composition, and compare the resulting synthetic spectral energy distributions with data from bright, early quasars. We show that only dust models with grain-size distributions in which small grains ($a\lesssim 0.1~\mu {\rm m}$, corresponding to $\approx 60{{\ \rm per\ cent}}$ of the total dust mass) are selectively removed from the dusty medium provide a good fit to the data. Removal can occur if small grains are efficiently destroyed in quasar environments and/or early dust production preferentially results in large grains. Attenuation curves for these models are close to flat, and consistent with recent data; they correspond to an effective dust-to-metal ratio fd ≃ 0.38, i.e. close to the Milky Way value.

The first measurement of the quasar lifetime distribution

ABSTRACT Understanding the growth of the supermassive black holes (SMBH) powering luminous quasars, their co-evolution with host galaxies, and impact on the surrounding intergalactic medium (IGM) depends sensitively on the duration of quasar accretion episodes. Unfortunately, this time-scale, known as the quasar lifetime, tQ, is still uncertain by orders of magnitude ($t_{\rm Q} \simeq 0.01\, {\rm Myr} - 1\, {\rm Gyr}$). However, the extent of the He ii Ly α proximity zones in the absorption spectra of zqso ∼ 3–4 quasars constitutes a unique probe, providing sensitivity to lifetimes up to ∼30 Myr. Our recent analysis of 22 archival Hubble Space Telescope He ii proximity zone spectra reveals a surprisingly broad range of emission time-scales, indicating that some quasars turned on ≲1 Myr ago, whereas others have been shining for ≳30 Myr. Determining the underlying quasar lifetime distribution (QLD) from proximity zone measurements is a challenging task owing to: (1) the limited sensitivity of individual measurements; (2) random sampling of the quasar light curves; (3) density fluctuations in the quasar environment; and (4) the inhomogeneous ionization state of He ii in a reionizing IGM. We combine a seminumerical He ii reionization model, hydrodynamical simulations post-processed with ionizing radiative transfer, and a novel statistical framework to infer the QLD from an ensemble of proximity zone measurements. Assuming a lognormal QLD, we infer a mean $\langle {\rm log}_{10}(t_{\rm Q} / {\rm Myr})\rangle = 0.22^{+0.22}_{-0.25}$ and standard deviation $\sigma _{{\rm log}_{10}t_{\rm Q}} = 0.80^{+0.37}_{-0.27}$. Our results allow us to estimate the probability of detecting very young quasars with tQ ≤ 0.1 Myr from their proximity zone sizes yielding $p ({\le}0.1\, {\rm Myr}) = 0.19^{+0.11}_{-0.09}$, which is broadly consistent with recent determination at z ∼ 6.

MUSE analysis of gas around galaxies (MAGG) – III. The gas and galaxy environment of z = 3–4.5 quasars

ABSTRACT We present a study of the environment of 27 z = 3–4.5 bright quasars from the MUSE Analysis of Gas around Galaxies (MAGG) survey. With medium-depth Multi Unit Spectroscopic Explorer (MUSE) observations (4 h on target per field), we characterize the effects of quasars on their surroundings by studying simultaneously the properties of extended gas nebulae and Ly α emitters (LAEs) in the quasar host haloes. We detect extended (up to ≈100 kpc) Ly α emission around all MAGG quasars, finding a very weak redshift evolution between z = 3 and z = 6. By stacking the MUSE datacubes, we confidently detect extended emission of C iv and only marginally detect extended He ii up to ≈40 kpc, implying that the gas is metal enriched. Moreover, our observations show a significant overdensity of LAEs within 300 $\rm km~s^{-1}$ from the quasar systemic redshifts estimated from the nebular emission. The luminosity functions and equivalent width distributions of these LAEs show similar shapes with respect to LAEs away from quasars suggesting that the Ly α emission of the majority of these sources is not significantly boosted by the quasar radiation or other processes related to the quasar environment. Within this framework, the observed LAE overdensities and our kinematic measurements imply that bright quasars at z = 3–4.5 are hosted by haloes in the mass range $\approx 10^{12.0}\small{--}10^{12.5}~\rm M_\odot$.

Faint Quasars Live in the Same Number Density Environments as Lyman Break Galaxies at z ∼ 4

Abstract Characterizing high-z quasar environments is key to understanding the coevolution of quasars and the surrounding galaxies. To restrict their global picture, we statistically examine the g-dropout galaxy overdensity distribution around 570 faint quasar candidates at z ∼ 4, based on the Hyper Suprime-Cam Subaru Strategic Program survey. We compare the overdensity significances of g-dropout galaxies around the quasars with those around g-dropout galaxies, and find no significant difference between their distributions. A total of 4 (22) out of the 570 faint quasars, , are found to be associated with the &gt;4σ overdense regions within an angular separation of 1.8 (3.0) arcmin, which is the typical size of protoclusters at this epoch. This is similar to the fraction of g-dropout galaxies associated with the &gt;4σ overdense regions. This result is consistent with our previous work in which and of luminous quasars detected in the Sloan Digital Sky Survey exist in the &gt;4σ overdense regions within 1.′8 and 3.′0 separations, respectively. Therefore, we suggest that the galaxy number densities around quasars are independent of their luminosity, and most quasars do not preferentially appear in the richest protocluster regions at z ∼ 4. The lack of an apparent positive correlation between the quasars and the protoclusters implies that (i) the gas-rich major merger rate is relatively low in the protocluster regions, (ii) most high-z quasars may appear through secular processes, or (iii) some dust-obscured quasars exist in the protocluster regions.

Absorption-line Environments of High-redshift BOSS Quasars

Abstract The early stage of massive galaxy evolution often involves outflows driven by a starburst or a central quasar plus cold mode accretion (infall), which adds to the mass build-up in the galaxies. To study the nature of these infall and outflows in the quasar environments, we have examined the correlation of narrow absorption lines (NALs) at positive and negative velocity shifts to other quasar properties, such as their broad absorption-line (BAL) outflows and radio-loudness, using spectral data from SDSS-BOSS DR12. Our results show that the incidence of associated absorption lines (AALs) and outflow AALs is strongly correlated with BALs, which indicates most AALs form in quasar-driven outflows. Multiple AALs are also strongly correlated with BALs, demonstrating quasar outflows tend to be highly structured and can create multiple gas components with different velocity shifts along our line of sight. Infall AALs appear less often in quasars with BALs than quasars without BALs. This suggests that BAL outflows act on large scale in host galaxies and inhibit the infall of gas from the IGM, supporting theoretical models in which quasar outflow plays an important role in the feedback to host galaxies. Despite having larger distances, infall AALs are more highly ionized than outflow AALs, which can be attributed to the lower densities in the infall absorbers.

The Role of Quasar Radiative Feedback on Galaxy Formation during Cosmic Reionization

Abstract Recent observations have found that many z ∼ 6 quasar fields lack galaxies. This unexpected lack of galaxies may potentially be explained by quasar radiation feedback. In this paper, I present a suite of 3D radiative transfer cosmological simulations of quasar fields. I find that quasar radiation suppresses star formation in low-mass galaxies, mainly by photodissociating their molecular hydrogen. Photo-heating also plays a role, but only after ∼100 Myr. However, galaxies that already have stellar mass above 105 M ⊙ when the quasar turns on will not be suppressed significantly. Quasar radiative feedback suppresses the faint end of the galaxy luminosity function (LF) within 1 pMpc, but to a far lesser degree than the field-to-field variation of the LF. My study also suggests that by using the number of bright galaxies ( &lt; −16) around quasars, we can potentially recover the underlying mass overdensity, which allows us to put reliable constraints on quasar environments.

Role of Intervening Mg ii Absorbers on the Rotation Measure and Fractional Polarization of the Background Quasars

Abstract We probed the magnetic fields in high-redshift galaxies using excess extragalactic contribution to residual rotation measure (RRM) for quasar sightlines with intervening Mg ii absorbers. Based on a large sample of 1132 quasars, we have computed RRM distributions broadening using median absolute deviation from the mean ( ), and found it to be 17.1 ± 0.7 rad m−2 for 352 sightlines having Mg ii intervening absorbers in comparison to its value of 15.1 ± 0.6 rad m−2 for 780 sightlines without such absorbers, resulting in an excess broadening ( ) of 8.0 ± 1.9 rad m−2 among these two subsamples. This value of , has allowed us to constrain the average strength of magnetic field (rest frame) in high-redshift galaxies responsible for these Mg ii absorbers, to be ∼1.3 ± 0.3 μG at a median redshift of 0.92. This estimate of magnetic field is consistent with the reported estimate in earlier studies based on radio-infrared correlation and energy equipartition for galaxies in the local universe. A similar analysis on subsample split based on the radio spectral index, α (with F ν ∝ ν α ), for flat (α ≥ −0.3; 315 sources) and steep (α ≤ −0.7; 476 sources) spectrum sources shows a significant (at 3.5σ level) for the former and absent in the latter. An anticorrelation found between the and percentage polarization (p) with a similar Pearson correlation of −0.62 and −0.87 for subsamples with and without Mg ii, respectively, suggests the main contribution for decrements in the p value to be intrinsic to the local environment of quasars.