A connection between extremely strong damped Lyman-αsystems and Lyman-αemitting galaxies at small impact parameters

Abstract

We present a study of ∼100 high redshift (z ∼ 2−4) extremely strong damped Lyman-α systems (ESDLA, with N(H i) ≥ 0.5 × 10 22 cm −2 ) detected in quasar spectra from the Baryon Oscillation Spectroscopic Survey (BOSS) of the Sloan Digital Sky Survey (SDSS-III) Data Release 11. We study the neutral hydrogen, metal, and dust content of this elusive population of absorbers and confirm our previous finding that the high column density end of the N(H i) frequency distribution has a relatively shallow slope with power-law index −3.6, similar to what is seen from 21-cm maps in nearby galaxies. The stacked absorption spectrum indicates a typical metallicity ∼1/20th solar, similar to the mean metallicity of the overall DLA population. The relatively small velocity extent of the low-ionisation lines suggests that ESDLAs do not arise from large-scale flows of neutral gas. The high column densities involved are in turn more similar to what is seen in DLAs associated with gamma-ray burst afterglows (GRB-DLAs), which are known to occur close to star-forming regions. This indicates that ESDLAs arise from a line of sight passing at very small impact parameters from the host galaxy, as observed in nearby galaxies. This is also supported by simple theoretical considerations and recent high-z hydrodynamical simulations. We strongly substantiate this picture by the first statistical detection of Ly α emission with L ESDLA (Ly α) (0.6 ± 0.2) × 10 42 erg s −1 in the core of ESDLAs (corresponding to about 0.1 L at z ∼ 2−3), obtained through stacking the fibre spectra (of radius 1 corresponding to ∼8 kpc at z ∼ 2.5). Statistical errors on the Ly α luminosity are of the order of 0.1 × 10 42 erg s −1 but we caution that the measured Ly α luminosity may be overestimated by ∼35% due to sky light residuals and/or FUV emission from the quasar host and that we have neglected flux-calibration uncertainties. We estimate a more conservative uncertainty of 0.2 × 10 42 erg s −1 . The properties of the Ly α line (luminosity distribution, velocity width and velocity offset compared to systemic redshift) are very similar to that of the population of Lyman-α emitting galaxies (LAEs) with L LAE (Ly α) ≥ 10 41 erg s −1 detected in long-slit spectroscopy or narrow-band imaging surveys. By matching the incidence of ESDLAs with that of the LAEs population, we estimate the high column density gas radius to be about r gas = 2.5 kpc, i.e., significantly smaller than the radius corresponding to the BOSS fibre aperture, making fibre losses likely negligible. Finally, the average measured Ly α luminosity indicates a star-formation rate consistent with the Schmidt-Kennicutt law, SFR (M yr −1 ) ≈ 0.6/ f esc , where f esc < 1 is the Ly α escape fraction. Assuming the typical escape fraction of LAEs, f esc ∼ 0.3, the Schmidt-Kennicutt law implies a galaxy radius of about r gal ≈ 2.5 kpc. Finally, we note that possible overestimation of the Ly α emission would result in both smaller r gas and r gal . Our results support a close association between LAEs and stro...

VLT/UVES observations of extremely strong intervening damped Lyman-αsystems

“…The tremendous increase of available quasar spectra (Pâris et al 2012 in the SDSS-III Baryon Oscillation Spectroscopic Survey (BOSS, Dawson et al 2013) allowed to extend the study to even higher column densities (Noterdaeme et al 2012b), with a slope similar to what is seen from opacity-corrected 21-cm maps in the local Universe (Braun 2012). The analysis of stacked spectra showed that extremely strong DLAs (ESDLAs, with log N(H i) ≥ 21.7) are likely to arise from galaxies at small impact parameters (b < a few kpc) with average star formation rates of the order of 2 M yr −1 (Noterdaeme et al 2014). X-shooter observations of a system with log N(H i) = 22.10 towards the quasar SDSS J113520.39−001053.5 resulted in the detection of a starforming galaxy at b < 1 kpc from the quasar line of sight (Noterdaeme et al 2012a; see also Kulkarni et al 2012), making it possible the first mass determination of a DLA galaxy by weak lensing (Grillo & Fynbo 2014).…”

EXPLORING DAMPED Lyα SYSTEM HOST GALAXIES USING GAMMA-RAY BURSTS

“…Also, DLA counterpart SFRs have been predicted to be higher for higher column densities and higher metallicities (Krumholz et al 2009;Gnedin & Kravtsov 2010;Rafelski et al 2011Rafelski et al , 2016Noterdaeme et al 2014;Rahmati & Schaye 2014). Our SFRs appear to be independent of column density in Figure yr 1 .…”

CO-dark molecular gas at high redshift: very large H2 content and high pressure in a low-metallicity damped Lyman alpha system

“…The measured H i column density is log N(H i)=21.82 ± 0.11, i.e. this DLA corresponds to a sub-class of DLA known as extremely strong DLAs (ESDLAs; Noterdaeme et al 2014). sis obtained from vpfit 3 and found a good match between the two approaches. All the errors quoted here are given using 63.8% quantile interval, which formally corresponds to 1σ interval for normal distribution 4 .…”