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.

We present a new method to quantify the value of the escape fraction of ionizing photons, and the existence of ultrafaint galaxies clustered around brighter objects during the epoch of cosmic reionization, using the diffuse Lyα, continuum, and Hα emission observed around galaxies at z 6 . We model the surface brightness profiles of the diffuse halos, considering the fluorescent emission powered by ionizing photons escaping from the central galaxies, and the nebular emission from satellite star-forming sources, by extending the formalisms developed in Mas-Ribas & Dijkstra and Mas-Ribas et al. The comparison between our predicted profiles and Lyα observations at z=5.7 and z=6.6 favors a low ionizing escape fraction, f 5% esc ion~, for galaxies in the range M 19 21.5 UV   --. However, uncertainties and possible systematics in the observations do not allow for firm conclusions. We predict Hα and restframe visible continuum observations with the James Webb Space Telescope (JWST), and show that it will be able to detect extended (a few tens of kiloparsecs) fluorescent Hα emission powered by ionizing photons escaping from a bright, L L 5 *  , galaxy. Such observations could differentiate fluorescent emission from nebular emission by satellite sources. We discuss how observations and stacking several objects may provide unique constraints on the escape fraction for faint galaxies and/or the abundance of ultra-faint radiation sources.

Direct collapse black holes forming in pristine, atomically-cooling haloes at z ≈ 10−20 may act as the seeds of supermassive black holes (BH) at high redshifts. In order to create a massive BH seed, the host halo needs to be prevented from forming stars. H 2 therefore needs to be irradiated by a large flux of Lyman-Werner (LW) UV photons in order to suppress H 2 cooling. A key uncertainty in this scenario is the escape fraction of LW radiation from first galaxies, the dominant source of UV photons at this epoch. To better constrain this escape fraction, we have performed radiation-hydrodynamical simulations of the growth of H ii regions and their associated photodissociation regions in the first galaxies using the ZEUS-MP code. We find that the LW escape fraction crucially depends on the propagation of the ionisation front (I-front). For an R-type I-front overrunning the halo, the LW escape fraction is always larger than 95%. If the halo recombines later from the outside-in, due to a softened and weakened spectrum, the LW escape fraction in the rest-frame of the halo (the near-field) drops to zero. A detailed and careful analysis is required to analyse slowly moving, D-type I-fronts, where the escape fraction depends on the microphysics and can be as small as 3% in the near-field and 61% in the far-field or as large as 100% in both the near-field and the far-field.

We revisit calculations of nebular hydrogen Lyα and HeII λ1640 line strengths for population III galaxies, undergoing continuous and bursts of star formation. We focus on initial mass functions (IMFs) motivated by recent theoretical studies, which generally span a lower range of stellar masses than earlier works. We also account for case-B departures and the stochastic sampling of the IMF. In agreement with previous works, we find that departures from case-B can enhance the Lyα flux by a factor of a few, but we argue that this enhancement is driven mainly by collisional excitation and ionization, and not due to photoionization from the n = 2 state of atomic hydrogen. The increased sensitivity of the Lyα flux to the high-energy end of the galaxy spectrum makes it more subject to stochastic sampling of the IMF. The latter introduces a dispersion in the predicted nebular line fluxes around the deterministic value by as much as a factor of ∼ 4. In contrast, the stochastic sampling of the IMF has less impact on the emerging Lyman Werner (LW) photon flux. When case-B departures and stochasticity effects are combined, nebular line emission from population III galaxies can be up to one order of magnitude brighter than predicted by 'standard' calculations that do not include these effects. This enhances the prospects for detection with future facilities such as JWST and large, groundbased telescopes.

We demonstrate the potential of line-intensity mapping to place constraints on the initial mass function (IMF) of Population III stars via measurements of the mean He ii 1640 Å/Hα line-intensity ratio. We extend the 21cmFAST code with modern high-redshift galaxy-formation and photoionization models, and estimate the line emission from Population II and Population III galaxies at redshifts 5 ≤ z ≤ 20. In our models, mean ratio values of He ii/H α ≳ 0.1 indicate top-heavy Population III IMFs with stars of several hundred solar masses, reached at z ≳ 10 when Population III stars dominate star formation. A next-generation space mission with capabilities moderately superior to those of CDIM will be able to probe this scenario by measuring the He ii and Hα fluctuation power spectrum signals and their cross-correlation at high significance up to z ∼ 20. Moreover, regardless of the IMF, a ratio value of He ii/Hα ≲ 0.01 indicates low Population III star formation and, therefore, it signals the end of the period dominated by this stellar population. However, a detection of the corresponding He ii power spectrum may be only possible for top-heavy Population III IMFs or through cross-correlation with the stronger Hα signal. Finally, ratio values of 0.01 ≲ He ii/Hα ≲ 0.1 are complex to interpret because they can be driven by several competing effects. We discuss how various measurements at different redshifts and the combination of the line-intensity ratio with other probes can assist in constraining the Population III IMF in this case.