Quasar Sightlines Research Articles

Investigation of the radial profile of galactic magnetic fields using rotation measure of background quasars

Probing magnetic fields in high-redshift galactic systems is crucial to investigate galactic dynamics and evolution. Utilizing the rotation measure of the background quasars, we have developed a radial profile of the magnetic field in a typical high-z galaxy. We have compiled a catalog of 59 confirmed quasar sightlines, having one intervening Mg II absorber in the redshift range 0.372 ≤ z abs ≤ 0.8. The presence of the foreground galaxy is ensured by comparing the photometric and spectroscopic redshifts within 3σ z-photo and visual checks. These quasar line-of-sights (LoS) pass through various impact parameters (D) up to 160 kpc, covering the circumgalactic medium of a typical Milky-Way type galaxy. Utilizing the residual rotation measure (RRM) of these sightlines, we estimated the excess in RRM dispersion, σ ex RRM. We found σ ex RRM decreases with increasing D. We translated σ ex RRM to average LoS magnetic field strength, 〈 B ∥ 〉 by considering a typical electron column density. Consequently, the decreasing trend is sustained in the magnetic field. In particular for sightlines with D ≤ 50 kpc and D> 50 kpc, 〈 B ∥ 〉 is found to be 2.39 ± 0.7 μG and 1.67 ± 0.38 μG, respectively. This suggests a clear indication of varying magnetic field from the disk to the circumgalactic medium. This work provides a methodology that, when applied to ongoing and future radio polarisation surveys such as LOFAR and SKA, promises to significantly enhance our understanding of magnetic field mapping in galactic systems.

The effect of cosmic rays on the observational properties of the CGM

ABSTRACT The circumgalactic medium (CGM) contains information on the cumulative effect of galactic outflows over time, generally thought to be caused by feedback from star formation and active galactic nuclei. Observations of such outflows via absorption in CGM gas of quasar sightlines show a significant amount of cold (${\lesssim}10^4\,{\rm K}$) gas, which cosmological simulations struggle to reproduce. Here, we use the adaptive mesh refinement hydrodynamical code Ramses to investigate the effect of cosmic rays (CR) on the cold gas content of the CGM using three zoom realizations of a z = 1 star-forming galaxy with supernova mechanical feedback: one with no CR feedback (referred to as no-CR), one with a medium CR diffusion coefficient $\kappa = 10^{28} \, \rm {cm^{2}\, s^{-1}}$ (CR−κmed), and one with a high rate of diffusion of $\kappa = 3\times 10^{29} \, \rm {cm^{2}\,\, s^{-1}}$ (CR−κhigh). We find that, for CR−κmed, the effects of CRs are largely confined to the galaxy itself as CRs do not extend far into the CGM. However, for CR−κhigh, the CGM temperature is lowered and the amount of outflowing gas is boosted. Our CR simulations fall short of the observed Mg ii covering fraction, a tracer of gas at temperatures ${\lesssim}10^4\,{\rm K}$, but the CR−κhigh simulation is more in agreement with covering fractions of C iv and O vi, which trace higher temperature gas.

The temperature of the neutral interstellar medium in the Galaxy

ABSTRACT Atomic Hydrogen-21 cm transition (H i) is an excellent tracer to study and understand the properties of the atomic gas in the Galaxy. Using the Westerbork Synthesis Radio Telescope, we observed 12 quasar sightlines to detect galactic H i in absorption. We achieve an optical depth rms of ∼1−2 × 10−3, essential to detect the warm neutral medium (WNM). We detect H i absorption in all our sightlines except along 1006+349, for which we set a strict upper limit on the spin temperature as 〈Ts〉 > 570 K. We find around 50 per cent of our sightlines have 〈Ts〉 > 500 K, indicating a WNM dominance. Further, we calculate an upper limit of the cold neutral medium (CNM) fraction along our sightlines and find a median CNM fraction of ∼0.12. With our observations, we reconfirm the existence of a threshold column density of ∼2 × 1020$\rm atoms \, cm^{-2}$ to form CNM in the interstellar medium (ISM). Using a two-temperature model of the H i disc, we explore the distribution of spin temperature in the Galactic ISM. We find that a simple fixed axisymmetric two-temperature model could not produce either the observed column density or the integral optical depth. This indicates the existence of a more complex distribution of spin temperatures in the Galaxy.

Large-scale excess H i absorption around z ≈ 4 galaxies detected in a background galaxy spectrum in the MUSE eXtremely deep field

ABSTRACT Observationally mapping the relation between galaxies and the intergalactic medium (IGM) is of key interest for studies of cosmic reionization. Diffuse hydrogen gas has typically been observed in H i Lyman-α (Lyα) absorption in the spectra of bright background quasars. However, it is important to extend these measurements to background galaxies as quasars become increasingly rare at high redshift and rarely probe closely separated sight lines. Here, we use deep integral field spectroscopy in the MUSE eXtremely Deep Field to demonstrate the measurement of the Lyα transmission at z ≈ 4 in absorption to a background galaxy at z = 4.77. The H i transmission is consistent with independent quasar sight lines at similar redshifts. Exploiting the high number of spectroscopic redshifts of faint galaxies (500 between z = 4.0–4.7 within a radius of 8 arcmin) that are tracers of the density field, we show that Lyα transmission is inversely correlated with galaxy density, i.e. transparent regions in the Lyα forest mark underdense regions at z ≈ 4. Due to large-scale clustering, galaxies are surrounded by excess H i absorption over the cosmic mean out to 4 cMpc/h70. We also find that redshifts from the peak of the Lyα line are typically offset from the systemic redshift by +170 km s−1. This work extends results from z ≈ 2–3 to higher redshifts and demonstrates the power of deep integral field spectroscopy to simultaneously measure the ionization structure of the IGM and the large-scale density field in the early Universe.

Detecting the Effect of Nonthermal Sources on the Warm-hot Galactic Halo

We report the first detection of nonthermal broadening of O vii lines in the warm-hot ≈106 K circumgalactic medium of the Milky Way. We use z = 0 absorption of O vii Kα, O vii Kβ, and O viii Kα lines in archival grating data of b > 15° quasar sightlines from Chandra and XMM-Newton. Nonthermal line broadening is evident in two-thirds of the sightlines considered, and on average is constrained at 4.6σ significance. Nonthermal line broadening dominates over thermal broadening. We extensively test whether the appearance of nonthermal line broadening could instead be because of multiple thermally broadened velocity components and robustly rule it out. Nonthermal line broadening is more evident toward sightlines at lower galactic latitude indicating the Galactic disk origin of the nonthermal sources. There is weak/no correlation between nonthermal line broadening and the angular separation of sightlines from the Galactic center, indicating that the nuclear region might not be a major source of nonthermal factors.

Cosmic Reionization on Computers: Statistics, Physical Properties, and Environments of Lyman Limit Systems at z ∼ 6

Lyman limit systems (LLSs) are dense hydrogen clouds with high enough H i column densities to absorb Lyman continuum photons emitted from distant quasars. Their high column densities imply an origin in dense environments; however, the statistics and distribution of LLSs at high redshifts still remain uncertain. In this paper, we use self-consistent radiative transfer cosmological simulations from the Cosmic Reionization on Computers (CROC) project to study the physical properties of LLSs at the tail end of cosmic reionization at z ∼ 6. We generate 3000 synthetic quasar sight lines to obtain a large number of LLS samples in the simulations. In addition, with the high physical fidelity and resolution of CROC, we are able to quantify the association between these LLS samples and nearby galaxies. Our results show that the fraction of LLSs spatially associated with nearby galaxies increases with H i column density. Moreover, we find that LLSs that are not near any galaxy typically reside in filamentary structures connecting neighboring galaxies in the intergalactic medium (IGM). This quantification of the distribution and association of LLSs to large-scale structure informs our understanding of the IGM–galaxy connection during the “Epoch of Reionization,” and provides a theoretical basis for interpreting future observations.

EIGER IV. The Cool 104 K Circumgalactic Environment of High-redshift Galaxies Reveals Remarkably Efficient Intergalactic Medium Enrichment

We report new observations of the cool diffuse gas around 29, 2.3 < z < 6.3 galaxies using deep JWST/NIRCam slitless grism spectroscopy around the sight line to the quasar J0100+2802. The galaxies span a stellar mass range of 7.1≤logM∗/M⊙≤10.7 , and star formation rates (SFRs) of −0.1<log SFR/M ⊙ yr−1 < 2.3. We find galaxies for seven Mg ii absorption systems within 300 kpc of the quasar sight line. The Mg ii radial absorption profile falls off sharply with radius, with most of the absorption extending out to 2–3 R 200 of the host galaxies. Six out of seven Mg ii absorption systems are detected around galaxies with logM∗/M⊙> 9. The Mg ii absorption kinematics are shifted from the systemic redshifts of host galaxies with a median absolute velocity ≈ 135 km s−1 and standard deviation ≈ 85 km s−1. The high kinematic offset and large radial separation (R > 1.3 R 200), suggest that five out of the seven Mg ii absorption systems are not gravitationally bound to their host galaxy. In contrast, most of the cool circumgalactic medium at z < 1 is gravitationally bound. The high incidence of unbound Mg ii gas in this work suggests that toward the end of reionization, galaxy halos are in a state of remarkable disequilibrium, and are highly efficient in enriching the intergalactic medium. The two strongest Mg ii absorption systems are detected at z ∼ 4.22 and 4.5, the former associated with a merging galaxy system and the latter associated with three kinematically close galaxies. Both of these galaxies reside in local galaxy overdensities, indicating the presence of cool Mg ii absorption in two “protogroups” at z > 4.

Metal enrichment and evolution in four z &gt; 6.5 quasar sightlines observed with JWST/NIRSpec

We present JWST/NIRSpec R ≃ 2700 spectra of four high-redshift quasars: VDES J0020–3653 (z = 6.860), DELS J0411–0907 (z = 6.825), UHS J0439+1634 (z = 6.519), and ULAS J1342+0928 (z = 7.535). The exquisite data quality, signal-to-noise ratio of 50–200, and large 0.86 μm ≤ λ ≤ 5.5 μm spectral coverage allowed us to identify between 13 and 17 intervening and proximate metal absorption line systems in each quasar spectrum, with a total number of 61 absorption-line systems detected at 2.42 &lt; z &lt; 7.48 including the highest redshift intervening O Iλ1302 and Mg II systems at z = 7.37 and z = 7.44. We investigated the evolution of the metal enrichment in the epoch of re-ionisation (EoR) at z &gt; 6 and found the following: i) a continued increase in the low-ionisation O I, C II, and Si II incidence, ii) decreasing high-ionisation C IV and Si IV incidence with a transition from predominantly high- to low-ionisation at z ≈ 6.0, and iii) a constant Mg II incidence across all redshifts. The observations support a change in the ionisation state of the intergalactic medium in the EoR rather than a change in metallicity. The abundance ratio of [Si/O] in five z &gt; 6 absorption systems show enrichment signatures produced by low-mass Pop III pair instability supernovae, and possibly Pop III hypernovae. In the Gunn-Peterson troughs, we detected transmission spikes where Lyα photons can escape. From 22 intervening absorption line systems at z &gt; 5.7, only a single low-ionisation system out of 13 lies within 2000 km s−1 from a spike, while four high-ionisation systems out of nine lie within ∼2000 km s−1 from a spike. Most spikes do not have associated metal absorbers close by. This confirms that star-forming galaxies responsible for producing the heavy elements that are transported to the circumgalactic medium via galaxy winds do so in predominantly high-density, neutral environments, while lower density environments are ionised without being polluted by metals at z ≈ 6 − 7.

Quasar Sightline and Galaxy Evolution (QSAGE) – III. The mass–metallicity and fundamental metallicity relation of z ≈ 2.2 galaxies

ABSTRACT We present analysis of the mass–metallicity relation (MZR) for a sample of 67 [O iii]-selected star-forming (SF) galaxies at a redshift range of z = 1.99−2.32 (zmed = 2.16) using Hubble Space Telescope Wide Field Camera 3 grism spectroscopy from the Quasar Sightline and Galaxy Evolution survey. Metallicities were determined using empirical gas-phase metallicity calibrations based on the strong emission lines [O ii]3727, 3729, [O iii]4959, 5007 and Hβ. SF galaxies were identified, and distinguished from active-galactic nuclei, via Mass–Excitation diagrams. Using z ∼ 0 metallicity calibrations, we observe a negative offset in the z = 2.2 MZR of ≈−0.51 dex in metallicity when compared to locally derived relationships, in agreement with previous literature analysis. A similar offset of ≈−0.46 dex in metallicity is found when using empirical metallicity calibrations that are suitable out to z ∼ 5, though our z = 2.2 MZR, in this case, has a shallower slope. We find agreement between our MZR and those predicted from various galaxy evolution models and simulations. Additionally, we explore the extended fundamental metallicity relation (FMR) which includes an additional dependence on star formation rate. Our results consistently support the existence of the FMR, as well as revealing an offset of 0.28 ± 0.04 dex in metallicity compared to locally derived relationships, consistent with previous studies at similar redshifts. We interpret the negative correlation with SFR at fixed mass, inferred from an FMR existing for our sample, as being caused by the efficient accretion of metal-poor gas fuelling SFR at cosmic noon.

The Relationship between IGM Lyα Opacity and Galaxy Density near the End of Reionization

Observed scatter in the Lyα opacity of quasar sightlines at z < 6 has motivated measurements of the correlation between Lyα opacity and galaxy density, as models that predict this scatter make strong and sometimes opposite predictions for how they should be related. Our previous work associated two highly opaque Lyα troughs at z ∼ 5.7 with a deficit of Lyα emitting galaxies (LAEs). In this work, we survey two of the most highly transmissive lines of sight at this redshift toward the z = 6.02 quasar SDSS J1306+0356 and the z = 6.17 quasar PSO J359-06. We find that both fields are underdense in LAEs within 10 h −1 Mpc of the quasar sightline, somewhat less extensive than underdensities associated with Lyα troughs. We combine our observations with three additional fields from the literature and find that while fields with extreme opacities are generally underdense, moderate opacities span a wider density range. The results at high opacities are consistent with models that invoke UV background fluctuations and/or late reionization to explain the observed scatter in intergalactic medium (IGM) Lyα opacities. There is tension at low opacities, however, as the models tend to associate lower IGM Lyα opacities with higher densities. Although the number of fields surveyed is still small, the low-opacity results may support a scenario in which the ionizing background in low-density regions increases more rapidly than some models suggest after becoming ionized. Elevated gas temperatures from recent reionization may also be making these regions more transparent.

On the Metallicities and Kinematics of the Circumgalactic Media of Damped Lyα Systems at z ∼ 2.5* * The data presented herein were obtained at the W. M. Keck Observatory, which is operated as a scientific partnership among the California Institute of Technology, the University of California and the National Aeronautics and Space Administration. The Observatory was made possible by

We use medium- and high-resolution spectroscopy of close pairs of quasars to analyze the circumgalactic medium (CGM) surrounding 32 damped Lyα absorption systems (DLAs). The primary quasar sightline in each pair probes an intervening DLA in the redshift range 1.6 < z abs < 3.5, such that the secondary sightline probes absorption from Lyα and a large suite of metal-line transitions (including O i, C ii, C iv, Si ii, and Si iv) in the DLA host galaxy’s CGM at transverse distances 24 kpc ≤ R ⊥ ≤ 284 kpc. Analysis of Lyα in the CGM sightlines shows an anticorrelation between R ⊥ and H i column density (N HI) with 99.8% confidence, similar to that observed around luminous galaxies. The incidences of C ii and Si ii with N > 1013 cm−2 within 100 kpc of DLAs are larger by 2σ than those measured in the CGM of Lyman break galaxies (C f (N CII ) > 0.89 and ). Metallicity constraints derived from ionic ratios for nine CGM systems with negligible ionization corrections and N HI > 1018.5 cm−2 show a significant degree of scatter (with metallicities/limits across the range ), suggesting inhomogeneity in the metal distribution in these environments. Velocity widths of C iv λ1548 and low-ionization metal species in the DLA versus CGM sightlines are strongly (>2σ) correlated, suggesting that they trace the potential well of the host halo over R ⊥ ≲ 300 kpc scales. At the same time, velocity centroids for C iv λ1548 differ in DLA versus CGM sightlines by >100 km s−1 for ∼50% of velocity components, but few components have velocities that would exceed the escape velocity assuming dark matter host halos of ≥1012 M ⊙.

Searching for dilaton fields in the Lyman- α forest

Dilatons (and moduli) couple to the masses and coupling constants of ordinary matter, and these quantities are fixed by the local value of the dilaton field. If, in addition, the dilaton with mass ${m}_{\ensuremath{\phi}}$ contributes to the cosmic dark matter density, then such quantities oscillate in time at the dilaton Compton frequency. We show how these oscillations lead to broadening and shifting of the Voigt profile of the Lyman-$\ensuremath{\alpha}$ forest in a manner that is correlated with the local dark matter density. We further show how tomographic methods allow the effect to be reconstructed by observing the Lyman-$\ensuremath{\alpha}$ forest spectrum of distant quasars. We then simulate a large number of quasar lines of sight using the lognormal density field, and forecast the ability of future astronomical surveys to measure this effect. We find that in the ultra low mass range ${10}^{\ensuremath{-}32}\text{ }\text{ }\mathrm{eV}\ensuremath{\le}{m}_{\ensuremath{\phi}}\ensuremath{\le}{10}^{\ensuremath{-}28}\text{ }\mathrm{eV}$ upcoming observations can improve over existing limits to the dilaton electron mass and fine structure constant couplings set by fifth force searches by up to five orders of magnitude. Our projected limits apply assuming that the ultralight dilaton makes up a few percent of the dark matter density, consistent with upper limits set by the cosmic microwave background anisotropies.

The physical origin for spatially large scatter of IGM opacity at the end of reionization: The IGM Lyα opacity-galaxy density relation

ABSTRACT The large opacity fluctuations in the z &amp;gt; 5.5 Lyα forest may indicate inhomogeneous progress of reionization. To explain the observed large scatter of the effective Lyα optical depth (τeff) of the intergalactic medium (IGM), fluctuation of UV background (Γ model), or the IGM gas temperature (T model) have been proposed, which predict opposite correlations between τeff and galaxy density. In order to address which model can explain the large scatter of τeff, we search for Lyα emitters (LAEs) around two (J1137+3549 and J1602+4228) quasar sightlines with τeff ∼ 3 and J1630+4012 sightline with τeff ∼ 5.5. Using a narrow-band imaging with Subaru/Hyper Suprime-Cam, we draw LAE density maps to explore their spatial distributions. Overdensities are found within 20 h−1 Mpc of the quasar sightlines in the low-τeff regions, while a deficit of LAEs is found in the high τeff region. Although the τeff of the three quasar sightlines are neither high nor low enough to clearly distinguish the two models, these observed τeff-galaxy density relations all consistently support the Γ model rather than the T model in the three fields, along with the previous studies. The observed overdensities near the low-τeff sightlines may suggest that the relic temperature fluctuation does not affect reionization that much. Otherwise, these overdensities could be attributed to other factors besides the reionization process, such as the nature of LAEs as poor tracers of underlying large-scale structures.

Measuring the thermal and ionization state of the low-z IGM using likelihood free inference

ABSTRACT We present a new approach to measure the power-law temperature density relationship $T=T_0 (\rho/ \bar{\rho })^{\gamma -1}$ and the UV background photoionization rate $\Gamma _{{{{\rm H\, {\small I}}}}{}}$ of the intergalactic medium (IGM) based on the Voigt profile decomposition of the Ly α forest into a set of discrete absorption lines with Doppler parameter b and the neutral hydrogen column density $N_{\rm H\, {\small I}}$. Previous work demonstrated that the shape of the $b-N_{{{{\rm H\, {\small I}}}}{}}$ distribution is sensitive to the IGM thermal parameters T0 and γ, whereas our new inference algorithm also takes into account the normalization of the distribution, i.e. the line-density dN/dz, and we demonstrate that precise constraints can also be obtained on $\Gamma _{{{{\rm H\, {\small I}}}}{}}$. We use density-estimation likelihood-free inference (DELFI) to emulate the dependence of the $b-N_{{{{\rm H\, {\small I}}}}{}}$ distribution on IGM parameters trained on an ensemble of 624 nyx hydrodynamical simulations at z = 0.1, which we combine with a Gaussian process emulator of the normalization. To demonstrate the efficacy of this approach, we generate hundreds of realizations of realistic mock HST/COS data sets, each comprising 34 quasar sightlines, and forward model the noise and resolution to match the real data. We use this large ensemble of mocks to extensively test our inference and empirically demonstrate that our posterior distributions are robust. Our analysis shows that by applying our new approach to existing Ly α forest spectra at z ≃ 0.1, one can measure the thermal and ionization state of the IGM with very high precision ($\sigma _{\log T_0} \sim 0.08$ dex, σγ ∼ 0.06, and $\sigma _{\log \Gamma _{{{{\rm H\, {\small I}}}}{}}} \sim 0.07$ dex).

Discovery of a Cool, Metal-rich Gas Reservoir in the Outskirts of z ≈ 0.5 Clusters

We built the first-ever statistically significant sample of ≈80,000 background quasar–foreground cluster pairs to study the cool, metal-rich gas in the outskirts (>R 500) of z ≈ 0.5 clusters with a median mass of ≈1014.2 M ⊙. The sample was obtained by crossmatching the Sloan Digital Sky Survey (SDSS) cluster catalog of Wen & Han and the SDSS quasar catalog of Lyke et al. The median impact parameter (ρ cl) of the clusters from the quasar sightlines is 2.4 Mpc (median ρ cl/R 500 = 3.6). A strong Mg II, along with marginal Fe II, absorption is detected in the mean and median stacked spectra of the quasars with a total Mg II rest-frame equivalent width () of 0.034 ± 0.005 Å (7σ) and 0.010 ± 0.003 Å (3σ), respectively. The shows a declining trend with increasing ρ cl and ρ cl/R 500, but does not show any significant trend with mass (M 500) or redshift (z cl) within the small M 500 and z cl ranges probed here. The Mg II absorption signal and the trends persist even if we exclude the quasar–cluster pairs where the background quasars may be probing the circumgalactic medium of bright galaxies with impact parameters <300 kpc. The Mg II (and Fe II) absorption reported here is the first detection of its kind. It indicates the presence of a cool, metal-rich gas reservoir surrounding galaxy clusters out to several R 500. We suggest that the metal-rich gas in the cluster outskirts arise from stripped materials and that gas stripping may be important out to large clustocentric distances (>3R 500).

Hydrogen reionization ends by z = 5.3: Lyman-α optical depth measured by the XQR-30 sample

ABSTRACT The presence of excess scatter in the Ly-α forest at z ∼ 5.5, together with the existence of sporadic extended opaque Gunn-Peterson troughs, has started to provide robust evidence for a late end of hydrogen reionization. However, low data quality and systematic uncertainties complicate the use of Ly-α transmission as a precision probe of reionization’s end stages. In this paper, we assemble a sample of 67 quasar sightlines at z &amp;gt; 5.5 with high signal-to-noise ratios of &amp;gt;10 per ≤15 km s−1 spectral pixel, relying largely on the new XQR-30 quasar sample. XQR-30 is a large program on VLT/X-Shooter which obtained deep (SNR &amp;gt; 20 per pixel) spectra of 30 quasars at z &amp;gt; 5.7. We carefully account for systematics in continuum reconstruction, instrumentation, and contamination by damped Ly-α systems. We present improved measurements of the mean Ly-α transmission over 4.9 &amp;lt; z &amp;lt; 6.1. Using all known systematics in a forward modelling analysis, we find excellent agreement between the observed Ly-α transmission distributions and the homogeneous-UVB simulations Sherwood and Nyx up to z ≤ 5.2 (&amp;lt;1σ), and mild tension (∼2.5σ) at z = 5.3. Homogeneous UVB models are ruled out by excess Ly-α transmission scatter at z ≥ 5.4 with high confidence (&amp;gt;3.5σ). Our results indicate that reionization-related fluctuations, whether in the UVB, residual neutral hydrogen fraction, and/or IGM temperature, persist in the intergalactic medium until at least z = 5.3 (t = 1.1 Gyr after the big bang). This is further evidence for a late end to reionization.

Measuring the Density Fields around Bright Quasars at z ∼ 6 with XQR-30 Spectra

Measuring the density of the intergalactic medium using quasar sight lines in the epoch of reionization is challenging due to the saturation of Lyα absorption. Near a luminous quasar, however, the enhanced radiation creates a proximity zone observable in the quasar spectra where the Lyα absorption is not saturated. In this study, we use 10 high-resolution (R ≳ 10,000) z ∼ 6 quasar spectra from the extended XQR-30 sample to measure the density field in the quasar proximity zones. We find a variety of environments within 3 pMpc distance from the quasars. We compare the observed density cumulative distribution function (CDF) with models from the Cosmic Reionization on Computers simulation and find a good agreement between 1.5 and 3 pMpc from the quasar. This region is far away from the quasar hosts and hence approaching the mean density of the universe, which allows us to use the CDF to set constraints on the cosmological parameter σ 8 = 0.6 ± 0.3. The uncertainty is mainly due to the limited number of high-quality quasar sight lines currently available. Utilizing the more than 200 known quasars at z ≳ 6, this method will allow us to tighten the constraint on σ 8 to the percent level in the future. In the region closer to the quasar within 1.5 pMpc, we find that the density is higher than predicted in the simulation by 1.23 ± 0.17, suggesting that the typical host dark matter halo mass of a bright quasar (M 1450 < −26.5) at z ∼ 6 is .

Observations of cold extragalactic gas clouds at z = 0.45 towards PKS 1610-771

ABSTRACT We present results from MUSE observations of a 21-cm ${\rm H\, {\small I}}$ absorption system detected with the Australian Square Kilometre Array Pathfinder radio telescope at redshift z = 0.4503 towards the z = 1.71 quasar PKS 1610-771. We identify four galaxies (A, B, X, and Y) at the same redshift as the 21-cm ${\rm H\, {\small I}}$ Damped Lyman-α (DLA) absorption system, with impact parameters ranging from less than 10 kpc to almost 200 kpc from the quasar sightline. ${\rm Ca\, {\small II}}$ and ${\rm Na\, {\small I}}$ absorption is seen in the MUSE spectrum of the background QSO, with velocities coinciding with the initial ${\rm H\, {\small I}}$ 21-cm detection, but tracing less dense and warmer gas. This metal-line component aligns with the rotating ionized disc of galaxy B (impact parameter 18 kpc from the QSO) and appears to be corotating with the galaxy disc. In contrast, the 21-cm ${\rm H\, {\small I}}$ absorber is blueshifted relative to the galaxies nearest the absorber and has the opposite sign to the velocity field of galaxy B. Since galaxies A and B are separated by only 17 kpc on the sky and 70 km s−1 in velocity, it appears likely that the 21-cm detection traces extragalactic clouds of gas formed from their interaction. This system reveals that the cold 100 K neutral gas critical for star formation can be associated with complex structures beyond the galaxy disc, and is a first case study made in preparation for future large 21-cm absorption surveys like the ASKAP First Large Absorption Survey in ${\rm H\, {\small I}}$.

Extremely strong DLAs at high redshift: gas cooling and H2 formation

ABSTRACT We present a spectroscopic investigation with the Very Large Telescope/X-shooter of seven candidate extremely strong damped Lyman-α absorption systems [ESDLAs, N(H i) ≥ 5 × 1021 cm−2] observed along quasar sightlines. We confirm the extremely high column densities, albeit slightly (0.1 dex) lower than the original ESDLA definition for four systems. We measured low-ionization metal abundances and dust extinction for all systems. For two systems, we also found strong associated H$\rm _2$ absorption $\log N(\rm{H\rm _2})\,\text{(cm$^{-2}$)}=18.16\pm 0.03$ and 19.28 ± 0.06 at z = 3.26 and 2.25 towards J2205+1021 and J2359+1354, respectively, while for the remaining five we measured conservative upper limits on the H$\rm _2$ column densities of typically $\log N(\rm{H\rm _2})\,\text{(cm$^{-2}$)}\,\lt\, 17.3$. The increased H2 detection rate (10–55 per cent at 68 per cent confidence level) at high H i column density compared with the overall damped Lyman-α population (∼5–10 per cent) confirms previous works. We find that these seven ESDLAs have similar observed properties as those previously studied towards quasars and γ-ray burst afterglows, suggesting they probe inner regions of galaxies. We use the abundance of ionized carbon at the excited fine-structure level to calculate the cooling rates through the C ii λ158 μm emission, and compare them with the cooling rates from damped Lyman-α systems in the literature. We find that the cooling rate distribution of ESDLAs also presents the same bimodality as previously observed for the general (mostly lower H i column density) damped Lyman-α population.

OUP accepted manuscript

We present an absorption line study of the physical and chemical properties of the Leo HI Ring and the Leo I Group as traced by 11 quasar sightlines spread over a 600 kpc X 800 kpc region. Using HST/COS G130/G160 archival observations as constraints, we couple cloud-by-cloud, multiphase, Bayesian ionization modeling with galaxy property information to determine the plausible origin of the absorbing gas along these sightlines. We search for absorption in the range 600 km/s - 1400 km/s consistent with the kinematics of the Leo Ring/Group. We find absorption plausibly associated with the Leo Ring towards five sightlines. Along three other sightlines, we find absorption likely to be associated with individual galaxies, intragroup gas, and/or large-scale filamentary structure. The absorption along these five sightlines is stronger in metal lines than expected from individual galaxies, indicative of multiple contributions, and of the complex kinematics of the region. We also identify three sightlines within a 7-degree X 6-degree field around the Leo Ring, along which we do not find any absorption. We find that the metallicities associated with the Leo Ring are generally high, with values between solar and several times solar. The inferred high metallicities are consistent with the origin of the ring as tidal debris from a major galaxy merger.