We present a measurement of the DLA mean bias from the cross-correlation of DLA and the Lyα forest, updating earlier results of Font-Ribera et al. (2012) with the final BOSS Data Release and an improved method to address continuum fitting corrections. Our cross-correlation is well fitted by linear theory with the standard ΛCDM model, with a DLA bias of b DLA = 1.99 ± 0.11; a more conservative analysis, which removes DLA in the Lyβ forest and uses only the cross-correlation at r > 10 h −1 Mpc, yields b DLA = 2.00 ± 0.19. This assumes the cosmological model from Planck Collaboration (2016) and the Lyα forest bias factors of Bautista et al. (2017), and includes only statistical errors obtained from bootstrap analysis. The main systematic errors arise from possible impurities and selection effects in the DLA catalogue, and from uncertainties in the determination of the Lyα forest bias factors and a correction for effects of high column density absorbers. We find no dependence of the DLA bias on column density or redshift. The measured bias value corresponds to a host halo mass ∼ 4 · 10 11 h −1 M if all DLA were hosted in halos of a similar mass. In a realistic model where host halos over a broad mass range have a DLA cross section Σ(M h ) ∝ M α h down to M h > M min = 10 8.5 h −1 M , we find that α > 1 is required to have b DLA > 1.7, implying a steeper relation or higher value of M min than is generally predicted in numerical simulations of galaxy formation.

Lyα halos are observed ubiquitously around star-forming galaxies at high redshift, but their origin is still a matter of debate. We demonstrate that the emission from faint unresolved satellite sources,  -M 17 UV , clustered around the central galaxies may play a major role in generating spatially extended Lyα, continuum (UV + VIS), and Hα halos. We apply the analytic formalism developed in Mas-Ribas & Dijkstra to model the halos around Lyman Alpha Emitters (LAEs) at z=3.1, for several different satellite clustering prescriptions. In general, our UV and Lyα surface brightness profiles match the observations well at   r 20 4 0 physical kpc from the centers of LAEs. We discuss how our profiles depend on various model assumptions and how these can be tested and constrained with future Hα observations by the James Webb Space Telescope (JWST). Our analysis shows how spatially extended halos constrain (i) the presence of otherwise undetectable satellite sources, (ii) the integrated, volumetric production rates of Lyα and LyC photons, and (iii) their population-averaged escape fractions. These quantities are all directly relevant for understanding galaxy formation and evolution and, for high enough redshifts, cosmic reionization.

We study the mean absorption spectrum of the Damped Lyman alpha population at z ∼ 2.6 by stacking normalized, rest-frame shifted spectra of ∼ 27 000 DLAs from the DR12 of BOSS/SDSS-III. We measure the equivalent widths of 50 individual metal absorption lines in 5 intervals of DLA hydrogen column density, 5 intervals of DLA redshift, and overall mean equivalent widths for an additional 13 absorption features from groups of strongly blended lines. The mean equivalent width of low-ionization lines increases with N HI , whereas for high-ionization lines the increase is much weaker. The mean metal line equivalent widths decrease by a factor ∼ 1.1 − 1.5 from z ∼ 2.1 to z ∼ 3.5, with small or no differences between low-and high-ionization species. We develop a theoretical model, inspired by the presence of multiple absorption components observed in high-resolution spectra, to infer mean metal column densities from the equivalent widths of partially saturated metal lines. We apply this model to 14 low-ionization species and to AlIII, SIII, SiIII, CIV, SiIV, NV and OVI. We use an approximate derivation for separating the equivalent width contributions of several lines to blended absorption features, and infer mean equivalent widths and column densities from lines of the additional species NI, ZnII, CII * , FeIII, and SIV. Several of these mean column densities of metal lines in DLAs are obtained for the first time; their values generally agree with measurements of individual DLAs from high-resolution, high signal-to-noise ratio spectra when they are available.

We quantify the contribution of Lyα fluorescence to observed spatially extended Lyα halos around Lyα emitters (LAE) at redshift z = 3.1. The key physical quantities that describe the fluorescent signal include (i) the distribution of cold gas in the circum-galactic medium (CGM); we explore simple analytic models and fitting functions to recent hydrodynamical simulations; (ii) local variations in the ionizing background due to ionizing sources that cluster around the central galaxy. We account for clustering by boosting the observationally inferred volumetric production rate of ionizing photons, LyC , by a factor 1 + ξ LyC (r), in which ξ LyC (r) quantifies the clustering of ionizing sources around the central galaxy. We compute ξ LyC (r) by assigning an "effective" bias parameter to the ionizing sources. This novel approach allows us to quantify our ignorance of the population of ionizing sources in a simple parametrized form. We find a maximum enhancement in the local ionizing background in the range 50 − 200 at r ∼ 10 physical kpc. For spatially uncorrelated ionizing sources and fluorescing clouds we find that fluorescence can contribute up to ∼ 50 − 60% of the observed spatially extended Lyα emission. We briefly discuss how future observations can shed light on the nature of Lyα halos around star forming galaxies.