ALBERT

Description: Using VLT/X-shooter, we searched for emission line galaxies associated with four damped Lyman α systems (DLAs) and one sub-DLA at 2.73 ≤ z ≤3.25 towards QSO J2358+0149. We detect [O iii ] emission from a ‘low-cool’ DLA at z abs = 2.9791 (having log N (H i ) = 21.69 ± 0.10, [Zn/H] = –1.83 ± 0.18) at an impact parameter of, ~ 12 kpc. The associated galaxy is compact with a dynamical mass of (1–6) x 10 9 M , very high excitation ([O iii ]/[O ii ] and [O iii ]/[Hβ] both greater than 10), 12+[O/H]≤8.5 and moderate star formation rate (SFR ≤2 M  yr –1 ). Such properties are typically seen in the low- z extreme blue compact dwarf galaxies. The kinematics of the gas is inconsistent with that of an extended disc and the gas is part of either a large scale wind or cold accretion. We detect Lyα emission from the z abs = 3.2477 DLA [having log N (H i ) = 21.12 ± 0.10 and [Zn/H] = –0.97 ± 0.13]. The Lyα emission is redshifted with respect to the metal absorption lines by 320 km s –1 , consistent with the location of the red hump expected in radiative transport models. We derive SFR ~0.2–1.7 M  yr –1 and Lyα escape fraction of ≥10 per cent. No other emission line is detected from this system. Because the DLA has a small velocity separation from the quasar (~500 km s –1 ) and the DLA emission is located within a small projected distance ( 〈 5 kpc), we also explore the possibility that the Lyα emission is being induced by the QSO itself. QSO-induced Lyα fluorescence is possible if the DLA is within a physical separation of 340 kpc to the QSO. Detection of stellar continuum light and/or the oxygen emission lines would disfavour this possibility. We do not detect any emission line from the remaining three systems.

Description: We present spectroscopic observations of six high redshift ( z em  〉 2) quasars, which have been selected for their Lyman α (Lyα) emission region being only partially covered by a strong proximate ( z abs  ~  z em ) coronagraphic damped Lyα system (DLA). We detected spatially extended Lyα emission envelopes surrounding these six quasars, with projected spatial extent in the range 26 ≤ d Lyα ≤ 51 kpc. No correlation is found between the quasar ionizing luminosity and the Lyα luminosity of their extended envelopes. This could be related to the limited covering factor of the extended gas and/or due to the AGN being obscured in other directions than towards the observer. Indeed, we find a strong correlation between the luminosity of the envelope and its spatial extent, which suggests that the envelopes are probably ionized by the AGN. The metallicity of the coronagraphic DLAs is low and varies in the range –1.75 〈 [Si/H] 〈 –0.63. Highly ionized gas is observed to be associated with most of these DLAs, probably indicating ionization by the central AGN. One of these DLAs has the highest Al iii /Si ii ratio ever reported for any intervening and/or proximate DLA. Most of these DLAs are redshifted with respect to the quasar, implying that they might represent infalling gas probably accreted on to the quasar host galaxies through filaments.

Description: We present an accurate analysis of the H 2 absorption lines from the z abs  ~ 2.4018 damped Lyα system towards HE 0027–1836 observed with the Very Large Telescope Ultraviolet and Visual Echelle Spectrograph (VLT/UVES) as a part of the European Southern Observatory Large Programme ‘The UVES large programme for testing fundamental physics’ to constrain the variation of proton-to-electron mass ratio, μ   m p / m e . We perform cross-correlation analysis between 19 individual exposures taken over three years and the combined spectrum to check the wavelength calibration stability. We notice the presence of a possible wavelength-dependent velocity drift especially in the data taken in 2012. We use available asteroids spectra taken with UVES close to our observations to confirm and quantify this effect. We consider single- and two-component Voigt profiles to model the observed H 2 absorption profiles. We use both linear regression analysis and Voigt profile fitting where μ/μ is explicitly considered as an additional fitting parameter. The two-component model is marginally favoured by the statistical indicators and we get μ/μ = –2.5 ± 8.1 stat  ± 6.2 sys ppm. When we apply the correction to the wavelength-dependent velocity drift, we find μ/μ = –7.6 ± 8.1 stat  ± 6.3 sys ppm. It will be important to check the extent to which the velocity drift we notice in this study is present in UVES data used for previous μ/μ measurements.

Description: We present a detailed analysis of absorption systems along the line of sight towards QSO PKS 0237–233 using a high-resolution spectrum of signal-to-noise ratio ~60–80 obtained with the Ultraviolet and Visual Echelle Spectrograph mounted on the Very Large Telescope (VLT/UVES). This line of sight is known to show a remarkable overdensity of C iv systems that has been interpreted as revealing the presence of a supercluster of galaxies. A detailed analysis of each of these absorption systems is presented. In particular, for the z abs  = 1.6359 (with two components of log N H I [cm –2 ] = 18.45, 19.05) and z abs  = 1.6720 (log N H I  = 19.78) sub-damped Lyα systems (sub-DLAs), we measure accurate abundances (resp. [O/H] = –1.63 ± 0.07 and [Zn/H] = –0.57 ± 0.05 relative to solar). While the depletion of refractory elements on to dust grains in both sub-DLAs is not noteworthy, photoionization models show that ionization effects are important in a part of the absorbing gas of the sub-DLA at z abs  = 1.6359 (H i is 95 per cent ionized) and in a part of the gas of the sub-DLA at z abs  = 1.6720. The C iv clustering properties along the line of sight is studied in order to investigate the nature of the observed overdensity. We conclude that despite the unusually high number of C iv systems detected along the line of sight, there is no compelling evidence for the presence of a single unusual overdensity and that the situation is consistent with chance coincidence.

Description: We present an analysis of the molecular hydrogen absorption system at z abs  = 2.811 in the spectrum of the blazar Q 0528–250. We demonstrate that the molecular cloud does not cover the background source completely. The partial coverage reveals itself as a residual flux at the bottom of the saturated H 2 absorption lines. This amounts to about (2.22 ± 0.54) per cent of the continuum and does not depend on the wavelength. This value is small and it explains why this effect has not been detected in previous studies of this quasar spectrum. However, it is robustly detected and is significantly higher than the zero-flux level at the bottom of the saturated lines of the Lyα forest, (–0.21 ± 0.22) per cent. The presence of the residual flux could be caused by unresolved quasar multicomponents, by light scattered by dust and/or by jet–cloud interaction. The H 2 absorption system is very well described by a two-component model without the inclusion of additional components when we take partial coverage into account. The derived total column densities in the H 2 absorption components A and B are log N (H 2 )(cm –2 ) = 18.10 ± 0.02 and 17.82 ± 0.02, respectively. HD molecules are present only in component B. Given the column density, log N (HD) = 13.33 ± 0.02, we find N (HD)/2 N (H 2 ) = (1.48 ± 0.10) x 10 – 5 , significantly lower than previous estimations. We argue that it is crucial to take into account the partial coverage effects in any analysis of H 2 bearing absorption systems, in particular when studying the physical state of the high-redshift interstellar medium.

Description: We present photometric and spectroscopic measurements of 53 QSO–galaxy pairs from the Sloan Digital Sky Survey (SDSS), where nebular emission lines from a 0 〈 z 〈 0.84 foreground galaxy are detected in the fibre spectra of a background QSO, bringing the overall sample to 103 QSO–galaxy pairs detected in the SDSS. We here study the nature of these systems. Detected foreground galaxies appear at impact parameters between 0.37 and 12.68 kpc. The presence of oxygen and Balmer emission lines allows us to determine the emission line metallicities for our sample, which are on average supersolar in value. Star formation rates for our sample are in the range 0.01–12 M  yr –1 . We utilize photometric redshift fitting techniques to estimate the M * values of our galaxies (log M * = 7.34–11.54), and extrapolate this relationship to those galaxies with no imaging detections. Where available, we measure the absorption features present in the QSO spectrum due to the foreground galaxy and the relationships between their rest equivalent widths. We report an anticorrelation between impact parameter and E ( B  –  V ) ( g  –  i ) , as well as a correlation between galaxy colour ( u  –  r ) and E ( B  –  V ) ( g  –  i ) . We find that our sample is one of late-type, star-forming galaxies comparable to field galaxies in a similar redshift range, providing important clues to better understand absorption systems. These galaxies represent a sample of typical galaxies in the local Universe for which abundances, extinction, morphology, and absorption properties may be measured using background QSOs with great potential for follow-up observations.

Description: We report long-slit spectroscopic observations of the quasar SDSS J082303.22+052907.6 ( $z_{\rm C\, {\small {IV}}}$  ~ 3.1875), whose broad-line region (BLR) is partly eclipsed by a strong damped Lyman α (DLA; log N (H i ) = 21.7) cloud. This allows us to study the narrow-line region (NLR) of the quasar and the Lyman α emission from the host galaxy. Using cloudy models that explain the presence of strong N v and P v absorption together with the detection of Si ii * and O i ** absorption in the DLA, we show that the density and the distance of the cloud to the quasar are in the ranges 180 〈  n H  〈 710 cm –3 and 580 〉  r 0  〉 230 pc, respectively. Sizes of the neutral (~2–9pc) and highly ionized phases (~3–80pc) are consistent with the partial coverage of the C iv BLR by the C iv absorption from the DLA (covering factor of ~0.85). We show that the residuals are consistent with emission from the NLR with C iv /Lyman α ratios varying from 0 to 0.29 through the profile. Remarkably, we detect extended Lyman α emission up to 25 kpc to the north and west directions and 15 kpc to the south and east. We interpret the emission as the superposition of strong emission in the plane of the galaxy up to 10 kpc with emission in a wind of projected velocity ~500 km s –1 which is seen up to 25 kpc. The low metallicity of the DLA (0.27 solar) argues for at least part of this gas being infalling towards the active galactic nucleus and possibly being located where accretion from cold streams ends up.

Description: We report the detection of a strong Milky Way-type 2175-Å extinction bump at z = 2.1166 in the quasar spectrum towards SDSS J121143.42+083349.7 from the Sloan Digital Sky Survey Data Release 10. We conduct follow up observations with the Echelle Spectrograph and Imager on-board the Keck II telescope and the Ultraviolet and Visual Echelle Spectrograph on the Very Large Telescope. This 2175-Å absorber is remarkable in that we simultaneously detect neutral carbon (C i ), neutral chlorine (Cl i ), and carbon monoxide (CO). It also qualifies as a damped Lyman α system. The J1211+0833 absorber is found to be metal rich and has a dust depletion pattern resembling that of the Milky Way disc clouds. We use the column densities of the C i fine structure states and the C ii /C i ratio (under the assumption of ionization equilibrium) to derive the temperature and volume density in the absorbing gas. A cloudy photoionization model is constructed, which utilizes additional atoms/ions to constrain the physical conditions. The inferred physical conditions are consistent with a canonical cold ( T ~ 100 K) neutral medium with a high density ( n (H i ) ~ 100 cm –3 ) and a slightly higher pressure than the local interstellar medium. Given the simultaneous presence of C i , CO, and the 2175-Å bump, combined with the high metallicity, high dust depletion level, and overall low ionization state of the gas, the absorber towards J1211+0833 supports the scenario that the presence of the bump requires an evolved stellar population.

Description: We present a detailed analysis of a red quasar at z = 2.32 with an intervening damped Lyman α absorber (DLA) at z = 2.13. Using high-quality data from the X-shooter spectrograph at ESO Very Large Telescope, we find that the absorber has a metallicity consistent with solar. We observe strong C i and H 2 absorption indicating a cold, dense absorbing medium. Partial coverage effects are observed in the C i lines, from which we infer a covering fraction of 27 ± 6 per cent and a physical diameter of the cloud of 0.1 pc. From the covering fraction and size, we estimate the size of the background quasar's broad line region. We search for emission from the DLA counterpart in optical and near-infrared imaging. No emission is observed in the optical data. However, we see tentative evidence for a counterpart in the H - and K '-band images. The DLA shows high depletion (as probed by [Fe/Zn] = –1.22) indicating that significant amounts of dust must be present in the DLA. By fitting the spectrum with various dust reddened quasar templates we find a best-fitting amount of dust in the DLA of A ( V ) DLA = 0.28 ± 0.01| stat ± 0.07| sys . We conclude that dust in the DLA is causing the colours of this intrinsically very luminous background quasar to appear much redder than average quasars, thereby not fulfilling the criteria for quasar identification in the Sloan Digital Sky Survey. Such chemically enriched and dusty absorbers are thus under-represented in current samples of DLAs.

Description: We present a systematic search for molecular hydrogen absorption systems at high redshift in quasar spectra from the Sloan Digital Sky Survey (SDSS)-II Data Release 7 and SDSS-III Data Release 9. We have selected candidates using a modified profile fitting technique taking into account that the Lyα forest can effectively mimic H 2 absorption systems at the resolution of SDSS data. To estimate the confidence level of the detections, we use two methods: a Monte Carlo sampling and an analysis of control samples. The analysis of control samples allows us to define regions of the spectral quality parameter space where H 2 absorption systems can be confidently identified. We find that H 2 absorption systems with column densities log N H 2 〉 19 can be detected in only less than 3 per cent of SDSS quasar spectra. We estimate the upper limit on the detection rate of saturated H 2 absorption systems (N H 2 〉 19) in damped Lyα (DLA) systems to be about 7 per cent. We provide a sample of 23 confident H 2 absorption system candidates that would be interesting to follow up with high-resolution spectrographs. There is a 1 r  –  i colour excess and non-significant A V extinction excess in quasar spectra with an H 2 candidate compared to standard DLA-bearing quasar spectra. The equivalent widths of C ii , Si ii and Al iii (but not Fe ii ) absorptions associated with H 2 candidate DLAs are larger compared to standard DLAs. This is probably related to a larger spread in velocity of the absorption lines in the H 2 -bearing sample.