Quasar Absorption Line Systems Research Articles

HIGH DUST DEPLETION IN TWO INTERVENING QUASAR ABSORPTION LINE SYSTEMS WITH THE 2175 Å EXTINCTION BUMP ATz∼ 1.4

We present the column densities of heavy-elements and dust depletion studies in twostrong Mg~II absorption systems at $z\sim1.4$ displaying the 2175-{\AA} dust extinction feature. Column densities are measured from low-ionization absorption lines using Apparent Optical Depth Method on the Keck/ESI spectra. We find the dust depletion patterns resemble to that of cold diffuse clouds in the Milky Way (MW). The values, [Fe/Zn]$\approx -1.5$ and [Si/Zn]$<-0.67$, are among the highest dust depletion measured for quasar absorption line systems. In another 2175-{\AA} absorber at $z$=1.64 toward the quasar SDSS J160457.50+220300.5, Noterdaeme et al. (2009) reported a similar dust depletion measurement ([Fe/Zn]=$-1.47$ and [Si/Zn]=$-1.07$) and detected C~I and CO absorption lineson its VLT/UVES spectrum. We conclude that heavy dust depletion (i.e. a characteristic of cold dense clouds in MW) is required to produce a pronounced 2175-{\AA} extinction bump.

Directly imaging damped Lyman α galaxies at z &gt; 2 - I. Methodology and first results★

We present the methodology for, and the first results from, a new imaging program aimed at identifying and characterizing the host galaxies of damped Lyman-alpha absorbers (DLAs) at z>2. We target quasar sightlines with multiple optically-thick HI absorbers and use the higher-redshift system as a "blocking filter" (via its Lyman-limit absorption) to eliminate all far-ultraviolet (FUV) emission from the quasar. This allows us to directly image the rest-frame FUV continuum emission of the lower-redshift DLA, without any quasar contamination and with no bias towards large impact parameters. We introduce a formalism based on galaxy number counts and Bayesian statistics with which we quantify the probability that a candidate is the DLA host galaxy. This method will allow the identification of a bona fide sample of DLAs that are too faint to be spectroscopically confirmed. The same formalism can be adopted to the study of other quasar absorption line systems (e.g. MgII absorbers). We have applied this imaging technique to two QSO sightlines. For the z~2.69 DLA towards J073149+285449, a galaxy with impact parameter b=1.54"=11.89 kpc and implied star formation rate (SFR) of ~5 M/yr is identified as the most reliable candidate. In the case of the z~2.92 DLA towards J211444-005533, no likely host is found down to a 3-sigma SFR limit of 1.4 M/yr. Studying the HI column density as a function of the impact parameter, including 6 DLAs with known hosts from the literature, we find evidence that the observed HI distribution is more extended than what is generally predicted from numerical simulation.

A CROSS-CORRELATION ANALYSIS OF Mg II ABSORPTION LINE SYSTEMS AND LUMINOUS RED GALAXIES FROM THE SDSS DR5

We analyze the cross-correlation of 2,705 unambiguously intervening Mg II (2796,2803A) quasar absorption line systems with 1,495,604 luminous red galaxies (LRGs) from the Fifth Data Release of the Sloan Digital Sky Survey within the redshift range 0.36<=z<=0.8. We confirm with high precision a previously reported weak anti-correlation of equivalent width and dark matter halo mass, measuring the average masses to be log M_h(M_[solar]h^-1)=11.29 [+0.36,-0.62] and log M_h(M_[solar]h^-1)=12.70 [+0.53,-1.16] for systems with W[2796A]>=1.4A and 0.8A<=W[2796A]<1.4A, respectively. Additionally, we investigate the significance of a number of potential sources of bias inherent in absorber-LRG cross-correlation measurements, including absorber velocity distributions and the weak lensing of background quasars, which we determine is capable of producing a 20-30% bias in angular cross-correlation measurements on scales less than 2'. We measure the Mg II - LRG cross-correlation for 719 absorption systems with v<60,000 km s^-1 in the quasar rest frame and find that these associated absorbers typically reside in dark matter haloes that are ~10-100 times more massive than those hosting unambiguously intervening Mg II absorbers. Furthermore, we find evidence for evolution of the redshift number density, dN/dz, with 2-sigma significance for the strongest (W>2.0A) absorbers in the DR5 sample. This width-dependent dN/dz evolution does not significantly affect the recovered equivalent width-halo mass anti-correlation and adds to existing evidence that the strongest Mg II absorption systems are correlated with an evolving population of field galaxies at z<0.8, while the non-evolving dN/dz of the weakest absorbers more closely resembles that of the LRG population.

Constraining Fundamental Constants of Physics with Quasar Absorption Line Systems

We summarize the attempts by our group and others to derive constraints on variations of fundamental constants over cosmic time using quasar absorption lines. Most upper limits reside in the range 0.5–1.5×10−5 at the 3σ level over a redshift range of approximately 0.5–2.5 for the fine-structure constant, α, the proton-to-electron mass ratio, μ and a combination of the proton gyromagnetic factor and the two previous constants, g p(α 2/μ)ν, for only one claimed variation of α. It is therefore very important to perform new measurements to improve the sensitivity of the numerous methods to at least <0.1×10−5 which should be possible in the next few years. Future instrumentations on ELTs in the optical and/or ALMA, EVLA and SKA pathfinders in the radio will undoutedly boost this field by allowing to reach much better signal-to-noise ratios at higher spectral resolution and to perform measurements on molecules in the ISM of high redshift galaxies.

Visualization of large scale structure from the Sloan Digital Sky Survey

We will discuss the challenges of visualizing large cosmological datasets. These include observational issues such as the masks and incomplete nature of the survey volume, cosmological issues such as redshift distortions and the difficulty of visualizing datasets that span cosmological epochs, as well as the inherent visualization challenges in presenting dense three-dimensional (3D) datasets. Two case studies will be presented. The first will feature the identification of filamentary structures in the large scale distribution of galaxies. The second case study will feature visualizations of the correlations between quasar absorption line systems and luminous red galaxies. Finally, we will give an overview of our visualization work-flow which features the use of the open-source 3D modeling program Blender.

Narrow associated quasi-stellar object absorbers: clustering, outflows and the line-of-sight proximity effect

Using data from the Sloan Digital Sky Survey data release 3 (SDSS DR3) we investigate how narrow (< 700km/s) C IV and Mg II quasar absorption line systems are distributed around quasars. The C IV absorbers lie in the redshift range 1:6 < z < 4 and the Mg II absorbers in the range 0:4 < z< 2:2. By correlating absorbers with quasars on different but nei ghbouring lines-of-sight, we measure the clustering of absorbers aro und quasars on comoving scales between 4 and 30 Mpc. The observed comoving correlation lengths are ro � 5h 1 Mpc, similar to those observed for bright galaxies at these redshifts. Co mparing with correlations between absorbers and the quasars in whose spectra they are identifie d then implies: (i) that quasars destroy absorbers to comoving distances of � 300kpc (C IV) and � 800kpc (Mg II) along their lines-of-sight; (ii) that & 40% of C IV absorbers within 3,000 km/s of the QSO are not a result of large-scale clustering but rather are directly a ssociated with the quasar itself; (iii) that this intrinsic absorber population extends to outflow v elocities of order 12,000 km/s; (iv) that this outflow component is present in both radio-loud and radio-quiet quasars; and (v) that a small high-velocity outflow component is observed in the Mg II population, but any further intrinsic absorber component is undetectable in our cluste ring analysis. We also find an indication that absorption systems within 3,000 km/s are more abundant for radio-loud than for radio-quiet quasars. This suggests either that radio-loud objects live in more massive halos, or that their radio activity generates an additional low-velo city outflow, or both.

Metal abundances at z &lt; 1.5: new measurements in sub-damped Lyman α absorbers

Damped Lyman-alpha systems (DLAs) and sub-DLAs seen toward background quasars provide the most detailed probes of elemental abundances. Somewhat paradoxically these measurements are more difficult at lower redshifts due to the atmospheric cut-off, and so a few years ago our group began a programme to study abundances at z < 1.5 in quasar absorbers. In this paper, we present new UVES observations of six additional quasar absorption line systems at z < 1.5, five of which are sub-DLAs. We find solar or above solar metallicity, as measured by the abundance of zinc, assumed not to be affected by dust, in two sub-DLAs: one, towards Q0138-0005 with [Zn/H]=+0.28 +/- 0.16; the other towards Q2335+1501 with [Zn/H]=+0.07 +/- 0.34. Relatively high metallicity was observed in another system: Q0123-0058 with [Zn/H]=-0.45 +/- 0.20. Only for the one DLA in our sample, in Q0449-1645, do we find a low metallicity, [Zn/H]=-0.96 +/- 0.08. We also note that in some of these systems large relative abundance variations from component to component are observed in Si, Mn, Cr and Zn.

The chemical compositions of 10 new sub-DLAs and strong Lyman-limit systems atz≲ 1.5

We present chemical abundance measurements from medium-resolution observations of eight subdamped Lya (sub-DLA) absorber and two strong Lyman-limit systems at z ≤ 1.5 observed with the Magellan Inamori Kyocera Echelle (MIKE) spectrograph on the 6.5-m Magellan II Clay telescope. These observations were taken as part of an ongoing project to determine abundances in z abs ≤ 1.5 quasar absorption line systems focusing on sub-DLA systems. These observations increase the sample of Zn measurements in z abs ≤ 1.5 sub-DLAs by ∼50 per cent. Lines of Mg i, Mg II, Al II, Al III, Can, Mn II, Fe II and Zn II were detected and column densities were determined. Zn II, a relatively undepleted element and tracer of the gas-phase metallicity is detected in two of these systems, with [Zn/H] = -0.05 ±0.12 and [Zn/H] > +0.86. The latter one is however a weak system with N H I < 18.8, and therefore may need significant ionization corrections to the abundances. Fe II lines were detected in all systems, with an average Fe abundance of ([Fe/H]) = -0.68, higher than typical Fe abundances for DLA systems at these redshifts. This high mean [Fe/H] could be due to less depletion of Fe on to dust grains, or to higher abundances in these systems. We also discuss the relative abundances in these absorbers. The systems with high metallicity show high ratios of [Mn/Fe] and [Zn/Fe], as seen previously in another sub-DLA. These higher values of [Mn/Fe] could be a result of heavy depletion of Fe on to grains, unmixed gas, or an intrinsically non-solar abundance pattern. Based on CLOUDY modelling, we do not expect ionization effects to cause this phenomenon.

Physical Properties of Weak MgiiAbsorbers atz ∼ 2

We present the results of photoionization modeling of nine weak Mg II (Wr < 0.3 A) quasar absorption-line systems with redshifts 1.4 < z < 2.4 obtained with the Ultraviolet and Visual Echelle Spectrograph on the Very Large Telescope. These systems have been chosen because they provide access to a regime of redshift space that previous weak Mg II studies have not looked at. The densities, metallicities, Doppler parameters, and column densities of these systems are compared to those of other weak Mg II systems at lower redshift. There is no significant statistical variation in the properties of the absorbers over the redshift range 0.4 < z < 2.4. The number density per unit redshift is known to decrease for weak Mg II absorbers between z ~ 1 and 2 by a greater amount than predicted from cosmological effects and changes in the extragalactic ionizing background alone. We suggest that, because the physical properties of the absorber population are not seen to change significantly across this range, the evolution in dN/dz is due to a decrease in the activity that gives rise to weak Mg II absorption, and not due to a change in the processes that form weak Mg II absorbers. The presence of separate, but aligned (in velocity) low- and high-density clouds in all single-cloud weak Mg II absorbers provides an important diagnostic of their geometry. We discuss possible origins in dwarf galaxies and in extragalactic analogs to high-velocity clouds.

On the Connection between Metal Absorbers and Quasar Nebulae

We establish a simple model for the distribution of cool (~10^4 K) gas around L* galaxies using the properties of strong Mg II absorption line systems as observational constraints. Our analysis suggests that the halos of L* galaxies are filled with cool gas clouds having sizes of order 1 kpc and densities of ~10^−2 cm^−3. We then investigate the physical conditions of a similar ensemble of clouds situated around a central quasar. We show that the flux from the quasar gives rise to (1) extended narrow line emission on ~100 kpc scales and (2) an anisotropy in the properties of the absorbing gas arising from the geometry of the quasar radiation field. Provided that quasars reside in gaseous halos more massive than those of L* galaxies, our predictions agree with the results from detections of both narrow emission line nebulae and ~100 kpc Mg II-absorbing halos around quasars, suggesting a common origin for these phenomena. We discuss the implications of our results for understanding quasar absorption line systems, quasar environments at high redshifts, and the quasar unification scheme.

The association between gas and galaxies - II. The two-point correlation function

We measure the two-point correlation function, TAG, between galaxies and quasar absorption-line systems at z 10 17 cm -2 . For C IV absorbers, the peak strength of ξ AG is roughly comparable to that of Hi absorbers with N HI > 10 16.5 cm -2 , consistent with the finding that the Civ absorbers are associated with strong Hi absorbers. We do not reproduce the differences reported by Chen et al. between ID TAG measurements using galaxy subsamples of different spectral types. However, the full impact on the measurements of systematic differences in our samples is hard to quantify. We compare the observations with smoothed particle hydrodynamical (SPH) simulations and discover that in the observations TAG is more concentrated to the smallest separations than in the simulations. The latter also display a 'finger of god' elongation of TAG along the LOS in redshift space, which is absent from our data, but similar to that found by Ryan-Weber for the cross-correlation of quasar absorbers and H I-emission-selected galaxies. The physical origin of these 'fingers of god' is unclear, and we thus highlight several possible areas for further investigation.

Life in the Universe: from the Miller Experiment to the Search for Life on Other Worlds

Life in the Universe: from the Miller Experiment to the Search for Life on Other Worlds

Supersolar Super-Lyman Limit Systems

We present abundance measurements for two super Lyman Limit systems (SLLS; quasar absorption line systems with 10^19 cm^-2 < N_HI < 10^20.3 cm^-2) selected from a set of metal-strong absorbers in the Sloan Digital Sky Survey quasar database. After applying estimate corrections for photoionization effects, we derive gas-phase metallicities of [M/H]=+0.7 +/- 0.2 dex for the SLLS at z=1.7749 toward SDSS0927+5621 and [M/H]=+0.05 +/- 0.1 dex for the SLLS at z=1.7678 toward SDSS0953+5230. The former exhibits among the highest gas metallicity of any astrophysical environment and its total metal surface density exceeds that of nearly every known damped Lya system. The properties of these absorbers -- high metallicity and large velocity width (> 300 km/s) -- resemble those of gas observed in absorption in the spectra of bright, star-forming galaxies at high redshift. We discuss the metal mass density of the SLLS based on these observations and our ongoing SLLS survey and argue that a conservative estimate to the total metal budget at z=2 is greater than 15% of the total, suggesting that the metal-rich LLS may represent the dominant metal reservoir in the young universe.

The Evolution of Neutral Gas in the Universe

AbstractWe give references to some of our work on the properties and evolution of the neutral gas component of the Universe (see reference list). The bulk of the observed neutral gas has been detected by identifying intervening damped Lyα (DLA) quasar absorption-line systems with N(H) ≥2 × 1020 atoms cm−2. We also present some initial results from a program to identify DLA absorbers near redshift z = 0.5 using Hubble Space Telescope ACS prism spectra (see Figure 1).

On the Importance of Local Sources of Radiation for Quasar Absorption Line Systems

A generic assumption of ionization models of quasar absorption systems is that radiation from local sources is negligible compared with the cosmological background. We test this assumption and find that it is unlikely to hold for absorbers as rare as H I Lyman limit systems. Assuming that the absorption systems are gas clouds centered on sources of radiation, we derive analytic estimates for the cross section-weighted moments of the flux seen by the absorbers, of the impact parameter, and of the luminosity of the central source. In addition, we compute the corresponding medians numerically. For the one class of absorbers for which the flux has been measured, damped Ly? systems at z ? 3, our prediction is in excellent agreement with the observations if we assume that the absorption arises in clouds centered on Lyman break galaxies. Finally, we show that consistency between observations of the UV background, the UV luminosity density from galaxies, and the number density of Lyman limit systems would require escape fractions of order 10%.

Dissecting the Circumstellar Environment of γ‐Ray Burst Progenitors

We investigate properties of the interstellar medium (ISM) in galaxies hosting long-duration γ-ray bursts (GRBs) from an analysis of atomic species (Mg0, Fe0) and excited fine-structure levels of ions (e.g., Si+). Our analysis is guided primarily by echelle observations of GRB 050730 and GRB 051111. These sight lines exhibit fine-structure transitions of O0, Si+, and Fe+ gas that have not yet been detected in intervening quasar absorption-line systems. Our results indicate that the gas with large Mg I equivalent width (e.g., GRB 051111) must occur at distances 50 pc from GRB afterglows to avoid photoionization. We examine the mechanisms for fine-structure excitation and find that two processes can contribute: (1) indirect UV pumping by the GRB afterglow provided a far-UV intensity in excess of 106 times the Galactic radiation field; and (2) collisional excitation in gas with electron density ne > 104 cm-3. The observed abundances of excited ions are well explained by UV pumping with the gas at r ~ a few hundred pc from the afterglow for GRB 051111 and r < 100 pc for GRB 050730, without invoking extreme gas density and temperature in the ISM. We show that UV pumping alone provides a simple explanation for all reported detections of excited ions in GRB afterglow spectra. The presence of strong fine-structure transitions therefore may offer little constraint for the gas density or temperature. We discuss additional implications of UV pumping including its impact on chemical abundance measurements, new prospects for observing line-strength variability, and future prospects for studying the gas density and temperature. Finally, we list a series of criteria that can distinguish between the mechanisms of UV pumping and collisional excitation.

Models of Five Absorption‐Line Systems along the Line of Sight Toward PG 0117+213

We present our investigation into the physical conditions of the gas in five intervening quasar absorption-line systems along the line of sight toward the quasar PG 0117+213, with redshifts of z ¼ 0:57, 0.72, 1.04, 1.32, and 1.34. Photoionization modeling of Hubble Space Telescope, Keck I, and Palomar data, using the code Cloudy, is employed to derive densities and metallicities of the multiple phases of gas required to fit the absorption profile for eachsystem.We discusstheimplicationsofthese models forgalaxy evolution,including theinterpretationof‘‘Civ �

DLAs in simulated galaxies and dust obscuration

We report here and use the results of a set of three-dimensional SPH/Treecode simulations which model the formation and early evolution of disk galaxies, including the generation of heavy elements by star formation, to investigate the effects of dust absorption in quasar absorption line systems. Using a simple prescription for the production of dust, we have compared the column density, zinc abundance, and optical depth properties of our models to the known properties of damped Lyman alpha systems. We find that a significant fraction of our model galaxy disks have a higher column density than any observed DLA system. We are also able to show that such parts of the disk tend to be optically thick, implying that any background quasar would be obscured through much of the disk. This would produce the selection effect against the denser absorption systems thought to be present in observations.

The MIKE/HIRES Lyman limit survey: first results

We present preliminary results of a detailed analysis of the such systems in an effort to accurately characterise this enigmatic and important class of quasar absorption line systems.

Low-redshift quasar absorption-line systems: inside and around galaxies

We present semi-analytic models and Monte-Carlo simulations of QSO Ly for a galaxy halo, in good agreement with observations. Using mock imaging and spectroscopic surveys, selection effects are found to be able to strengthen the anti-correlation between line width and projected distance. The models were also applied to quasar metal absorption lines and more realistic absorption spectra with noise were simulated.