Metal-line Absorption Systems Research Articles

Metal enrichment and evolution in four z > 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 < z < 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 > 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 > 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 > 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.

EIGER. I. A Large Sample of [O iii]-emitting Galaxies at 5.3 < z < 6.9 and Direct Evidence for Local Reionization by Galaxies

We present a first sample of 117 [O iii] λλ4960, 5008–selected star-forming galaxies at 5.33 < z < 6.93 detected in JWST/NIRCam 3.5 μm slitless spectroscopy of a field centered on the hyperluminous quasar SDSS J0100+2802, obtained as part of the Emission-line galaxies and Intergalactic Gas in the Epoch of Reionization (EIGER) survey. Three prominent galaxy overdensities are observed, one of them at the redshift of the quasar. Galaxies are found within 200 pkpc and 105 km s−1 of four known metal absorption-line systems. We focus on the role of the galaxies in ionizing the intergalactic medium (IGM) during the later stages of cosmic reionization and construct the mean Lyα and Lyβ transmission as a function of distance from the galaxies. At the lowest redshifts in our study, 5.3 < z < 5.7, the IGM transmission rises monotonically with distance from the galaxies, as seen previously at lower redshifts. In contrast, at 5.7 < z < 6.14, the transmission of both Lyα and Lyβ first increases with distance but then peaks at a distance of 5 cMpc before declining. Finally, in the region 6.15 < z < 6.26, where the additional ionizing radiation from the quasar dominates, the monotonic increase in transmission with distance is reestablished. This result is interpreted to represent evidence that the transmission of the IGM at z ∼ 5.9 toward J0100+2802 results from the “local” ionizing radiation of galaxies that dominates over the much-reduced cosmic background.

Characterizing the abundance, properties, and kinematics of the cool circumgalactic medium of galaxies in absorption with SDSS DR16

ABSTRACT In order to study the circumgalactic medium (CGM) of galaxies we develop an automated pipeline to estimate the optical continuum of quasars and detect intervening metal absorption line systems with a matched kernel convolution technique and adaptive S/N criteria. We process ∼ one million quasars in the latest Data Release 16 (DR16) of the Sloan Digital Sky Survey (SDSS) and compile a large sample of ∼ 160 000 Mg ii absorbers, together with ∼ 70 000 Fe ii systems, in the redshift range 0.35 &amp;lt; zabs &amp;lt; 2.3. Combining these with the SDSS DR16 spectroscopy of ∼1.1 million luminous red galaxies (LRGs) and ∼200 000 emission line galaxies (ELGs), we investigate the nature of cold gas absorption at 0.5 &amp;lt; z &amp;lt; 1. These large samples allow us to characterize the scale dependence of Mg ii with greater accuracy than in previous work. We find that there is a strong enhancement of Mg ii absorption within ∼50 kpc of ELGs, and the covering fraction within 0.5rvir of ELGs is 2–5 times higher than for LRGs. Beyond 50 kpc, there is a sharp decline in Mg ii for both kinds of galaxies, indicating a transition to the regime where the CGM is tightly linked with the dark matter halo. The Mg ii-covering fraction correlates strongly with stellar mass for LRGs, but weakly for ELGs, where covering fractions increase with star formation rate. Our analysis implies that cool circumgalactic gas has a different physical origin for star-forming versus quiescent galaxies.

Modelling intergalactic low ionization metal absorption line systems near the epoch of reionization

ABSTRACT We interpret observations of intergalactic low ionization metal absorption systems at redshifts z ≳ 5 in terms of pressure-confined clouds. We find clouds confined by the expected pressure of galactic haloes with masses $11\lt \log M_h/h^{-1}\, \mathrm{M}_\odot \lt 12$ provide a good description of the column density ratios between low ionization metal absorbers. Some of the ratios, however, require extending conventional radiative transfer models of irradiated slabs to spherical (or cylindrical) clouds to allow for lines of sight passing outside the cores of the clouds. Moderate depletion of silicon on to dust grains is also indicated in some systems. The chemical abundances inferred span the range between solar and massive-star-dominated stellar populations as may arise in starburst galaxies. The typical H i column densities matching the data correspond to damped Ly α absorbers (DLAs) or sub-DLAs, with sizes of 40 pc to 3 kpc, gas masses 3.5 &amp;lt; log Mc/M⊙ &amp;lt; 8 and metallicites $0.001\!-\!0.01\, \mathrm{Z}_\odot$. Such systems continue to pose a challenge for galaxy-scale numerical simulations to reproduce.

Identifying Mg ii narrow absorption lines with deep learning

Metal absorption line systems in distant quasar spectra probe of the history of gas content in the universe. The MgII $\lambda \lambda$ 2796, 2803 doublet is one of the most important absorption lines since it is a proxy of the star formation rate and a tracer of the cold gas associated with high redshift galaxies. Machine learning algorithms have been used to detect absorption lines systems in large sky surveys, such as Principle Component Analysis (PCA), Gaussian Process (GP) and decision trees. A very powerful algorithm in the field of machine learning called deep neural networks, or '' deep learning'' is a new structure of neural network that automatically extracts semantic features from raw data and represents them at a high level. In this paper, we apply a deep convolutional neural network for absorption line detection. We use the previously published DR7 MgII catalog (Zhu et al. 2013) as the training and validation sample and the DR12 MgII catalog as the test set. Our deep learning algorithm is capable of detecting MgII absorption lines with an accuracy of $\sim$94% . It takes only $\sim 9$ seconds to analyze $\sim$ 50000 quasar spectra with our deep neural network, which is ten thousand times faster than traditional methods, while preserving high accuracy with little human interference. Our study shows that Mg II absorption line detection accuracy of a deep neutral network model strongly depends on the filter size in the filter layer of the neural network, and the best results are obtained when the filter size closely matches the absorption feature size.

A deep search for metals near redshift 7: the line of sight towards ULAS J1120+0641

We present a search for metal absorption line systems at the highest redshifts to date using a deep (30h) VLT/X-Shooter spectrum of the z = 7.084 quasi-stellar object (QSO) ULAS J1120+0641. We detect seven intervening systems at z > 5.5, with the highest-redshift system being a C IV absorber at z = 6.51. We find tentative evidence that the mass density of C IV remains flat or declines with redshift at z < 6, while the number density of C II systems remains relatively flat over 5 < z < 7. These trends are broadly consistent with models of chemical enrichment by star formation-driven winds that include a softening of the ultraviolet background towards higher redshifts. We find a larger number of weak ( W_rest < 0.3A ) Mg II systems over 5.9 < z < 7.0 than predicted by a power-law fit to the number density of stronger systems. This is consistent with trends in the number density of weak Mg II systems at z = 2.5, and suggests that the mechanisms that create these absorbers are already in place at z = 7. Finally, we investigate the associated narrow Si IV, C IV, and N V absorbers located near the QSO redshift, and find that at least one component shows evidence of partial covering of the continuum source.

Fluctuations of the intergalactic ionization field at redshiftz~ 2

(Abridged) Aims. To probe the spectral energy distribution (SED) of the ionizing background radiation at z ~ 2 and to specify the sources contributing to the intergalactic radiation field. Methods. The spectrum of a bright quasar HS1103+6416 (zem = 2.19) contains five successive metal-line absorption systems at zabs = 1.1923, 1.7193, 1.8873, 1.8916, and 1.9410. The systems are optically thin and reveal multiple lines of different metal ions with the ionization potentials lying in the extreme ultraviolet (EUV) range (1 Ryd to 0.2 keV). For each system, the EUV SED of the underlying ionization field is reconstructed by means of a special technique developed for solving the inverse problem in spectroscopy. For the zabs = 1.8916 system, the analysis also involves the HeI resonance lines of the Lyman series and the HeI 504 A continuum, which are seen for the first time in any cosmic object except the Sun. Results. From one system to another, the SED of the ionizing continuum changes significantly, indicating that the intergalactic ionization field at z ~ 2 fluctuates at the scale of at least Delta_z ~ 0.004. This is consistent with Delta_z ~ 0.01 estimated from HeII and HI Lyman-alpha forest measurements between the redshifts 2 and 3.

HIGH-REDSHIFT METALS. II. PROBING REIONIZATION GALAXIES WITH LOW-IONIZATION ABSORPTION LINES AT REDSHIFT SIX $^,$

We present a survey for low-ionization metal absorption line systems towards 17 QSOs at redshifts z_em=5.8-6.4. Nine of our objects were observed at high resolution with either Keck/HIRES or Magellan/MIKE, and the remainder at moderate resolution with Keck/ESI. The survey spans 5.3 < z_abs < 6.4 and has a pathlength interval \Delta X=39.5, or \Delta z=8.0. In total we detect ten systems, five of which are new discoveries. The line-of-sight number density is consistent with the combined number density at z~3 of DLAs and sub-DLAs, which comprise the main population of low-ionization systems at lower redshifts. This apparent lack of evolution may occur because low ionization systems are hosted by lower-mass halos at higher redshifts, or because the mean cross section of low-ionization gas at a given halo mass increases with redshift due to the higher densities and lower ionizing background. The roughly constant number density notably contrasts with the sharp decline at z > 5.3 in the number density of highly-ionized systems traced by C IV. The low-ionization systems at z~6 span a similar range of velocity widths as lower-redshift sub-DLAs but have significantly weaker lines at a given width. This implies that the mass-metallicity relation of the host galaxies evolves towards lower metallicities at higher redshifts. These systems lack strong Si IV and C IV, which are common among lower-redshift DLAs and sub-DLAs. This is consistent, however, with a similar decrease in the metallicity of the low- and high-ionization phases, and does not necessarily indicate a lack of nearby, highly-ionized gas. The high number density of low-ionization systems at z~6 suggests that we may be detecting galaxies below the current limits of i-dropout and Ly-alpha emission galaxy surveys. These systems may therefore be the first direct probes of the `typical' galaxies responsible for hydrogen reionization.

A KENNICUTT-SCHMIDT LAW FOR INTERVENING ABSORPTION LINE SYSTEMS

We argue that most strong intervening metal absorption line systems, where the rest equivalent width of the MgII 2796A line is >0.5A, are interstellar material in, and outflowing from, star-forming disks. We show that a version of the Kennicutt-Schmidt law is readily obtained if the MgII equivalent widths are interpreted as kinematic broadening from absorbing gas in outflowing winds originating from star-forming galaxies. Taking a phenomenological approach and using a set of observational constraints available for star-forming galaxies, we are able to account for the density distribution of strong MgII absorbers over cosmic time. The association of intervening material with star-forming disks naturally explains the metallicity and dust content of strong MgII systems as well as their high HI column densities, and does not require the advection of metals from compact star-forming regions into the galaxy halos to account for the observations. We find that galaxies with a broad range of luminosities can give rise to absorption of a given rest-equivalent width, and discuss possible observational strategies to better quantify true galaxy-absorber associations and further test our model. We show that the redshift evolution in the density of absorbers closely tracks the star formation history of the universe and that strong intervening systems can be used to directly probe the physics of both bright and faint galaxies over a broad redshift range. By identifying strong intervening systems with galaxy disks and quantifying a version of the Kennicutt-Schmidt law that applies to them, a new probe of the interstellar medium is found which provides complementary information to that obtained through emission studies of galaxies. Implications of our results for galaxy feedback and enrichment of the intergalactic medium are discussed. [abridged]

Constraining the Intergalactic Medium Enrichment History with QSO Pairs

AbstractIntergalactic metals are ubiquitous, but their sources remain unknown. A key constraint on these sources is the spatial distributions of metals. Yet, the clustering of metals is difficult to interpret along single lines-of-sight, because distance and velocity information are mixed in redshift space. To overcome this situation we are carrying out detailed comparisons between the line-of-sight and transverse distributions of metal line absorption systems observed in a large sample of QSO pairs and simulations including a wide range of IGM-enrichment scenarios. The degeneracy between distance and velocity is broken by the transverse information available in pairs of sightlines, and thus these comparisons are providing unique new constraints on when and where metals were ejected from galaxies.

Metal-line system survey: characterizing the low-redshift IGM

The low-redshift IGM probes the last ten billion years of metal enrichment from galactic feedback processes. We present preliminary results from a survey of intergalactic metal-line absorption systems in archival HST STIS, GHRS, and FUSE spectra of ≈50 z≲2 UV-bright objects. We summarize the detailed analysis of one sightline (PKS1302–102, z QSO =0.2784) with which we set the methodology for the larger survey. We use simple CLOUDY models to constrain the ionizing mechanism(s) and metallicities for the metal-line systems. For about 15 sightlines, including PKS1302–102, we have a complementary galaxy survey, and we look for correlations between galaxies and absorption systems in order to understand the large-scale distribution of the metal-enriched IGM.

Correlations between O vi Absorbers and Galaxies at Low Redshift

We investigate the relationship between galaxies and metal-line absorption systems in a large-scale cosmological simulation with galaxy formation. Our detailed treatment of metal enrichment and non-equilibrium calculation of oxygen species allow us, for the first time, to carry out quantitative calculations of the cross-correlations between galaxies and O VI absorbers. We find the following: (1) The cross-correlation strength depends weakly on the absorption strength but strongly on the luminosity of the galaxy. (2) The correlation distance increases monotonically with luminosity from ~0.5-1h^-1 Mpc for 0.1L* galaxies to ~3-5h^-1 Mpc for L* galaxies. (3) The correlation distance has a complicated dependence on absorber strength, with a luminosity-dependent peak. (4) Only 15% of O VI absorbers lie near >=Lz* galaxies. The remaining 85%, then, must arise ``near'' lower-luminosity galaxies, though, the positions of those galaxies is not well-correlated with the absorbers. This may point to pollution of intergalactic gas predominantly by smaller galaxies. (5) There is a subtle trend that for >~0.5Lz* galaxies, there is a positive correlation between absorber strength and galaxy luminosity in the sense that stronger absorbers have a slightly higher probability of finding such a large galaxy at a given projection distance. For less luminous galaxies, there seems to be a negative correlation between luminosity and absorber strength.

Characterizing the Low‐Redshift Intergalactic Medium toward PKS 1302−102

We present a detailed analysis of the intergalactic metal-line absorption systems in the archival HST STIS and FUSE ultraviolet spectra of the low-redshift quasar PKS 1302?102 ( -->zQSO = 0.2784). We supplement the archive data with CLOUDY ionization models and a survey of galaxies in the quasar field. There are 15 strong Ly? absorbers with column densities --> NH I > 14. Of these, six are associated with at least C III ?977 absorption [ -->log N(C+ +) > 13]; this implies a redshift density --> dNC III/dz = 36-9+13 (68% confidence limits) for the five detections with rest equivalent width -->Wr > 50 m?. Two systems show O VI ??1031, 1037 absorption in addition to C III [ -->log N(O+ 5) > 14]. One is a partial Lyman limit system (--> log NH I = 17) with associated C III, O VI, and Si III ?1206 absorption. There are three tentative O VI systems that do not have C III detected. For one O VI doublet with both lines detected at 3 ? with -->Wr > 50 m?, --> dNO VI/dz = 7-4+9. We also search for O VI doublets without Ly? absorption but identify none. From CLOUDY modeling, these metal-line systems have metallicities spanning the range ? -->4 [ M/H ] ? 0.3. The two O VI systems with associated C III absorption cannot be single-phase, collisionally ionized media based on the relative abundances of the metals and kinematic arguments. From the galaxy survey, we discover that the absorption systems are in a diverse set of galactic environments. Each metal-line system has at least one galaxy within 500 km s?1 and 600 -->h?175 kpc with -->L > 0.1L*.

Spectral shape of the UV ionizing background and He II absorption at redshifts 1.8 &lt; z &lt; 2.9

Aims. The shape of the UV ionizing background is reconstructed from optically thin metal absorption-line systems identified in spectra of HE 2347–4342, Q 1157+3143, and HS 1700+6416 in the redshift interval $1.8 Methods. The systems are analyzed by means of the Monte Carlo Inversion method completed with the spectral shape recovering procedure. Results. The UVB spectral shape fluctuates at $2.4 2.4$, the recovered spectral shapes show intensity depression between 3 and 4 Ryd due to $\ion{He}{ii}$ Ly α absorption in the IGM clouds (line blanketing) and continuous medium (true Gunn-Petersen effect). The mean $\ion{He}{ii}$ Ly α opacity estimated from the depth of this depression corresponds within 1-2 σ to the values directly measured from the $\ion{H}{i}$/$\ion{He}{ii}$ Ly α forest towards the quasars studied. The observed scatter in $\eta = N$($\ion{He}{ii}$)/ N ($\ion{H}{i}$) and anti-correlation between N ($\ion{H}{i}$) and η can be explained by the combined action of variable spectral softness and differences in the mean gas density between the absorbing clouds. Neither of the recovered spectral shapes show features which can be attributed to the putative input of radiation from soft sources like starburst galaxies.

Lyα Absorption in the Quasar Triplet Q0107-025A, Q0107-025B, and Q0107-0232: Data Calibration and Line Selection

We present spectroscopic observations for quasars Q0107-025A, Q0107-025B, and Q0107-0232. For the first time, all data obtained with the Hubble Space Telescope's GHRS and FOS for these three quasars are combined. Lyα absorbers selected from the spectra can be used to trace the coherence of the intergalactic medium (IGM) on scales of 1-2 h Mpc over the redshift range 0.4 < za < 0.9. A new analysis of double and triple absorber coincidences derived from the improved spectra is performed. Automated line-selection algorithms were used to detect absorption lines in the QSO spectra; coincident absorbers were identified across two and three sight lines based on their proximity to each other in velocity space. A control simulation designed to generate artificial absorption-line spectra was used to gauge the significance of the coincidences. Four intervening metal-line absorption systems are detected, with three of the four coincident to the A and B sight lines and one coincident across all three sight lines. This is evidence for substantial clustering among the objects responsible for the metal-enriched gas. By contrast, large-scale coherence of the IGM gas is detectable but weak. Fewer than half of the absorbers are coincident on scales of 1-2 h Mpc, a result that is significant at the 99% confidence level, and coherence arises preferentially in the higher column density gas. Triple absorber coincidences occur at a level that is significant at the 99% confidence level, which indicates that the higher column density gas has a planar geometry.

Multi-object spectroscopy of the field surrounding PKS 2126-158: discovery of a z= 0.66 galaxy group

The high-redshift radio-loud quasar PKS 2126-158 is found to have a large number of red galaxies in close apparent proximity. We use the Gemini Multi-Object Spectrograph (GMOS) on Gemini South to obtain optical spectra for a large fraction of these sources. We show that there is a group of galaxies at $z\sim0.66$, coincident with a metal-line absorption system seen in the quasar's optical spectrum. The multiplexing capabilities of GMOS also allow us to measure redshifts of many foreground galaxies in the field surrounding the quasar. The galaxy group has five confirmed members, and a further four fainter galaxies are possibly associated. All confirmed members exhibit early-type galaxy spectra, a rare situation for a Mg II absorbing system. We discuss the relationship of this group to the absorbing gas, and the possibility of gravitational lensing of the quasar due to the intervening galaxies.

Discovery of a Dwarf Poststarburst Galaxy near a High Column Density Local Lyα Absorber

We report the discovery of a dwarf (MB = -13.9) poststarburst galaxy coincident in recession velocity (within uncertainties) with the highest column density absorber (NH i = 1015.85 cm-2 at cz = 1586 km s-1) in the 3C 273 sight line. This galaxy is by far the closest galaxy to this absorber, projected just 71 h kpc on the sky from the sight line. The mean properties of the stellar populations in this galaxy are consistent with a massive starburst ≈3.5 Gyr ago, whose attendant supernovae, we argue, could have driven sufficient gas from this galaxy to explain the nearby absorber. Beyond its proximity on the sky and in recession velocity, the further evidence in favor of this conclusion includes both a match in the metallicities of absorber and galaxy and the fact that the absorber has an overabundance of Si/C, suggesting recent Type II supernova enrichment. Thus, this galaxy and its ejecta are in the expected intermediate stage in the fading dwarf evolutionary sequence envisioned by Babul & Rees to explain the abundance of faint blue galaxies at intermediate redshifts. While this one instance of a QSO metal-line absorber and a nearby dwarf galaxy is not proof of a trend, a similar dwarf galaxy would be too faint to be observed by galaxy surveys around more distant metal-line absorbers. Thus, we cannot exclude the possibility that dwarf galaxies are primarily responsible for weak (NH i = 1014-1017 cm-2) metal-line absorption systems in general. If a large fraction of the dwarf galaxies expected to exist at high redshift had a similar history (i.e., they had a massive starburst that removed all or most of their gas), these galaxies could account for at least several hundred high-z metal-line absorbers along the line of sight to a high-z QSO. The volume-filling factor for this gas, however, would be less than 1%.

Spectroscopic Identification of Faint White Dwarf Candidates in the Praesepe Open Star Cluster

We present spectroscopic observations of four previously unidentified candidate white dwarfs (WDs) in Praesepe. All four candidates are quasars with redshifts between 0.8 and 2.8. One quasar, LB 6072, is observed to have a strong metal-line absorption system blueward of the quasar redshift. The lack of additional WDs in Praesepe leaves the total known WD population of the cluster at five, well below the number expected from commonly assumed initial mass functions, although several undiscovered cluster WDs may lie in the outer regions of the cluster. All known Praesepe member WDs are concentrated within 06 of the cluster center, and the radial profile of cluster WDs is quite similar to the profile of massive cluster stars. This profile is mildly inconsistent with that of ~1 M⊙ cluster stars and suggests that the WDs did not receive a velocity kick during the progenitor star's mass-loss phase. If complete, the observed Praesepe WD population is consistent with a steeper high-end initial mass function than is commonly assumed, although the calculated slopes are inconsistent with the present-day mass function of Praesepe. Searches for WDs outside the core of Praesepe and further study of the WD populations of additional open clusters are necessary to constrain further the underlying cause of the WD deficit.

A New Hi21 Centimeter Absorber Associated with the HiDeficient Interacting Galaxies G0248+430

We present high-resolution (~2'') H I 21 cm and CO(1-0) observations of the quasar (QSO) galaxy pair 0248+430. The QSO Q0248+430 (zem = 1.313) has been found to show two metal absorption-line systems at redshifts za ~ 0.052, which are consistent with the redshift of a foreground luminous infrared galaxy 15'' (~11 h-1 kpc) away. In our observations, the CO emission of this foreground galaxy, G0248+430, shows broad velocity distribution (~173 km s-1) but is spatially confined to a small unresolved region less than 1.5 × 1.5 h-1 kpc; the H2 mass based on the traditional conversion factor is ≈1010 M☉, which is approximately 30 times the H2 mass within a similar region of the Milky Way. On the other hand, no significant H I 21 cm emission is found in the foreground galaxy; the mass of the neutral atomic hydrogen is less than 6 × 108 M☉. Toward the QSO we discover a new H I 21 cm absorber with τ dv ~ 0.26 km s-1 at the redshift of one of the metal absorption components; however, we did not detect significant CO(1-0) absorption toward the QSO. The H I column density is large enough for the absorber to be classified as a damped Lyα system. We also derive the H I mass and spin temperature for this metal-line absorption system. We discuss the relation of this H I absorber and the depletion of the H I in the foreground galaxy. We find that this H I absorber has very high metal abundance and is intrinsically different from the normal damped Lyα absorption systems, although both have similar spin temperatures and hydrogen column densities.

SDSS J1650+4251: A New Gravitational Lens

We report that the Sloan Digital Sky Survey quasar SDSS J165043.44+425149.3 is gravitationally lensed into two images, based on observations obtained with the WIYN 3.5 m telescope at the Kitt Peak National Observatory. The lensed quasar, at a redshift of z=1.54, appears as two images separated by 1.2" with B-band magnitudes of 17.8 and 20.0. The lensing galaxy is clearly detected in I-band images obtained in 0.3" seeing, after point spread function subtraction of the two quasar images. A strong metal-line absorption system is also identified in the unresolved SDSS spectrum of the double quasar, suggesting a plausible lens redshift of z=0.58. The UBRI flux ratios of the pair vary significantly from 8.5:1 in the blue to 5.4:1 in the red, a difference of 0.5 magnitudes, and may indicate the presence of microlensing in one or both quasar components. The predicted differential time delay between quasar images is on the order of one month, assuming the intervening absorption system is due to the lensing galaxy.