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: Energy & Fuels DOI: 10.1021/acs.energyfuels.6b01323

Description: This paper presents a survey of X-ray-selected active galactic nuclei (AGNs) with optical spectroscopic follow-up in a ~ 18 deg 2 area of the equatorial XMM-XXL north field. A sample of 8445 point-like X-ray sources detected by XMM–Newton above a limiting flux of $F_{\rm 0.5{\rm -}10\, keV} 〉 10^{-15} \rm \,erg\, cm^{-2}\, s^{-1}$ was matched to optical (Sloan Digital Sky Survey, SDSS) and infrared (IR; WISE ) counterparts. We followed up 3042 sources brighter than r = 22.5 mag with the SDSS Baryon Oscillation Spectroscopic Survey (BOSS) spectrograph. The spectra yielded a reliable redshift measurement for 2578 AGNs in the redshift range z = 0.02–5.0, with 0.5-2 keV luminosities ranging from 10 39 -10 46 erg s – 1 . This is currently the largest published spectroscopic sample of X-ray-selected AGNs in a contiguous area. The BOSS spectra of AGN candidates show a distribution of optical line widths which is clearly bimodal, allowing an efficient separation between broad- and narrow-emission line AGNs. The former dominate our sample (70 per cent) due to the relatively bright X-ray flux limit and the optical BOSS magnitude limit. We classify the narrow-emission line objects (22 per cent of the full sample) using standard optical emission line diagnostics: the majority have line ratios indicating the dominant source of ionization is the AGN. A small number (8 per cent of the full sample) exhibit the typical narrow line ratios of star-forming galaxies, or only have absorption lines in their spectra. We term the latter two classes ‘elusive’ AGN, which would not be easy to identify correctly without their X-ray emission. We also compare X-ray ( XMM–Newton ), optical colour (SDSS) and and IR ( WISE ) AGN selections in this field. X-ray observations reveal, by far, the largest number of AGN. The overlap between the selections, which is a strong function of the imaging depth in a given band, is also remarkably small. We show using spectral stacking that a large fraction of the X-ray AGNs would not be selectable via optical or IR colours due to host galaxy contamination. A substantial fraction of AGN may therefore be missed by these longer wavelength selection methods.

Description: We present a tentative detection of the large-scale structure of Ly α emission in the Universe at redshifts z = 2–3.5 by measuring the cross-correlation of Ly α surface brightness with quasars in Sloan Digital Sky Survey/Baryon Oscillation Spectroscopic Survey. We use a million spectra targeting luminous red galaxies at z 〈 0.8, after subtracting a best-fitting model galaxy spectrum from each one, as an estimate of the high-redshift Ly α surface brightness. The quasar–Ly α emission cross-correlation is detected on scales 1 ~ 15 h –1 Mpc, with shape consistent with a CDM model with $\Omega _{\rm m} =0.30^{+0.10}_{-0.07}$ . The predicted amplitude of this cross-correlation is proportional to the product of the mean Ly α surface brightness, 〈μ α 〉, the amplitude of mass fluctuations and the quasar and Ly α emission bias factors. We infer 〈μ α 〉 ( b α /3) = (3.9 ± 0.9) x 10 –21 erg s –1  cm –2 Å –1  arcsec –2 , where b α is the Ly α emission bias. If star-forming galaxies dominate this emission, we find SFR = (0.28 ± 0.07)(3/ b α ) yr –1  Mpc –3 . For b α = 3, this value is ~30 times larger than previous estimates from individually detected Ly α emitters, but consistent with the total SFR derived from dust-corrected, continuum UV galaxy surveys, if most of the Ly α photons from these galaxies avoid dust absorption and are reemitted after diffusing in large gas haloes. Heating of intergalactic gas by He ii photoionization from quasar radiation or jets may alternatively explain the detected correlation, and cooling radiation from gas in galactic haloes may also contribute. We also detect redshift space anisotropy of the quasar–Ly α emission cross-correlation, finding evidence at the 3.0 level that it is radially elongated, which may be explained by radiative-transfer effects. Our measurements represent the first application of the intensity mapping technique to optical observations.

Description: Deuterium is created during big bang nucleosynthesis, and, in contrast to the other light stable nuclei, can only be destroyed thereafter by fusion in stellar interiors. In this Letter, we study the cosmic evolution of the deuterium abundance in the interstellar medium (ISM) and its dispersion using realistic galaxy evolution models. We find that models that reproduce the observed metal abundance are compatible with observations of the deuterium abundance in the local ISM and z  ~ 3 absorption line systems. In particular, we reproduce the low astration factor which we attribute to a low global star formation efficiency. We calculate the dispersion in deuterium abundance arising from different structure formation histories in different parts of the Universe. Our model also predicts a tight correlation between deuterium and metal abundances which could be used to measure the primordial deuterium abundance.

Description: We report the discovery of the first ‘ghostly’ damped Ly α absorption system (DLA), which is identified by the presence of absorption from strong low-ion species at z abs = 1.704 65 along the line of sight to the quasar SDSS J113341.29–005740.0 with z em = 1.704 41. No Ly α absorption trough is seen associated with these absorptions because the DLA trough is filled with the leaked emission from the broad emission-line region of the quasar. By modelling the quasar spectrum and analysing the metal lines, we derive log  N (H i )(cm –2 ) ~21.0 ± 0.3. The DLA cloud is small (≤0.32 pc), thus not covering entirely the broad-line region and is located at ≥39 pc from the central active galactic nucleus (AGN). Although the DLA is slightly redshifted relative to the quasar, its metallicity ([S/H] = –0.41 ± 0.30) is intermediate between what is expected from infalling and outflowing gas. It could be possible that the DLA is part of some infalling material accreting on to the quasar host galaxy through filaments, and that its metallicity is raised by mixing with the enriched outflowing gas emanating from the central AGN. Current DLA surveys miss these ‘ghostly’ DLAs, and it would be important to quantify the statistics of this population by searching the Sloan Digital Sky Survey (SDSS) data base using metal absorption templates.

Description: We present the results from our search for H i 21-cm absorption in a sample of 16 strong Fe ii systems [ W r (Mg ii 2796) ≥ 1.0 Å and W r (Fe ii 2600) or $W_{{\rm Fe\,\small {II}}}$ ≥ 1 Å] at 0.5 〈 z 〈 1.5 using the Giant Metrewave Radio Telescope and the Green Bank Telescope. We report six new H i 21-cm absorption detections from our sample, which have increased the known number of detections in strong Mg ii systems at this redshift range by ~50 per cent. Combining our measurements with those in the literature, we find that the detection rate of H i 21-cm absorption increases with $W_{{\rm Fe\,\small {II}}}$ , being four times higher in systems with $W_{{\rm Fe\,\small {II}}}$ ≥ 1 Å compared to systems with $W_{{\rm Fe\,\small {II}}}$ 〈 1 Å. The N ( ${\rm H\,\small {I}}$ ) associated with the H i 21-cm absorbers would be ≥2 x 10 20  cm –2 , assuming a spin temperature of ~500 K (based on H i 21-cm absorption measurements of damped Lyman α systems at this redshift range) and unit covering factor. We find that H i 21-cm absorption arises on an average in systems with stronger metal absorption. We also find that quasars with H i 21-cm absorption detected towards them have systematically higher E ( B – V ) values than those which do not. Further, by comparing the velocity widths of H i 21-cm absorption lines detected in absorption- and galaxy-selected samples, we find that they show an increasing trend (significant at 3.8) with redshift at z 〈 3.5, which could imply that the absorption originates from more massive galaxy haloes at high z . Increasing the number of H i 21-cm absorption detections at these redshifts is important to confirm various trends noted here with higher statistical significance.

Description: We present the results from our survey of H  i 21-cm absorption, using Giant Metrewave Radio Telescope, Very Large Array and Westerbork Radio Synthesis Telescope, in a sample of 55 z  〈 0.4 galaxies towards radio sources with impact parameters ( b ) in the range ~0–35 kpc. In our primary sample (defined for statistical analyses) of 40 quasar-galaxy pairs, probed by 45 sightlines, we have found seven H  i 21-cm absorption detections, two of which are reported here for the first time. Combining our primary sample with measurements having similar optical depth sensitivity (d v ≤ 0.3 km s –1 ) from the literature, we find a weak anti-correlation (rank correlation coefficient = –0.20 at 2.42 level) between d v and b , consistent with previous literature results. The covering factor of H  i 21-cm absorbers ( C 21 ) is estimated to be 0.24 $^{+0.12}_{-0.08}$ at b ≤ 15 kpc and 0.06 $^{+0.09}_{-0.04}$ at b  = 15–35 kpc. d v and C 21 show similar declining trend with radial distance along the galaxy's major axis and distances scaled with the effective H  i radius. There is also tentative indication that most of the H  i 21-cm absorbers could be co-planar with the extended H  i discs. No significant dependence of d v and C 21 on galaxy luminosity, stellar mass, colour and star formation rate is found, though the H  i 21-cm absorbing gas cross-section may be larger for the luminous galaxies. The higher detection rate (by a factor of ~4) of H  i 21-cm absorption in z  〈 1 damped Lyman-α systems compared to the quasar-galaxy pairs indicates towards small covering factor and patchy distribution of cold gas clouds around low- z galaxies.