We present Monte Carlo calculations of Lyα radiative transfer through optically thick, spherically symmetric, collapsing gas clouds. These represent simplified models of proto-galaxies that are caught in the process of their assembly. Such galaxies produce Lyα flux over an extended solid angle, either from a spatially extended Lyα emissivity, or from scattering effects, or both. We present a detailed study of the effect of the gas distribution and kinematics, and of the Lyα emissivity profile, on the emergent spectrum and surface brightness distribution. The emergent Lyα spectrum is typically double-peaked and asymmetric. In practice, however, we find that energy transfer from the infalling gas to the Lyα photons -together with a reduced escape probability for photons in the red wing-causes the blue peak to be significantly enhanced and the red peak, in most cases, to be undetectable. This results in an effective blueshift, which, combined with scattering in the intergalactic medium, will render extended Lyα emission from collapsing protogalaxies difficult to detect beyond redshift z ∼ > 4. We find that scattering flattens the surface brightness profile in clouds with large line center optical depths (τ 0 > 10 5 ). A strong wavelength dependence of the slope of the surface brightness distribution (with preferential flattening at the red side of the line) would be a robust indication that Lyα photons are being generated (rather than just scattered) in a spatially extended, collapsing region around the galaxy. We also find that for self-ionized clouds whose effective Lyα optical depth is ∼ < 10 3 , infall and outflow models can produce nearly identical spectra and surface brightness distributions, and are difficult to distinguish from one another. The presence of deuterium with a cosmic abundance may produce a narrow but detectable dip in the spectra of systems with moderate hydrogen column densities, in the range 10 18 − 10 20 cm −2 . Finally, we present a new analytic solution for the emerging Lyα spectrum in the limiting case of a static uniform sphere, extending previous solutions for static plane-parallel slabs.

We present the final results from our ultra-deep spectroscopic campaign with FORS2 at the ESO/VLT for the confirmation of z ≃ 7 "z-band dropout" candidates selected from our VLT/Hawk-I imaging survey over three independent fields. In particular we report on two newly discovered galaxies at redshift ∼ 6.7 in the NTT deep field: both galaxies show a Lyα emission line with rest-frame EWs of the order 15-20Å and luminosities of 2-4×10 42 ergs −1 . We also present the results of ultra-deep observations of a sample of i-dropout galaxies, from which we set a solid upper limit on the fraction of interlopers.Out of the 20 z-dropouts observed we confirm 5 galaxies at 6.7 < z < 7.1. This is systematically below the expectations drawn on the basis of lower redshift observations: in particular there is a significant lack of objects with intermediate Lyα EWs (between 20 and 55Å). We conclude that the trend for the fraction of Lyα emission in LBGs that is constantly increasing from z∼3 to z∼6 is most probably reversed from z ∼ 6 to z∼7. Explaining the observed rapid change in the LAE fraction among the drop-out population with reionization requires a fast evolution of the neutral fraction of hydrogen in the Universe. Assuming that the Universe is completely ionized at z=6 and adopting the semi-analytical models of Dijkstra et al. (2011), we find that our data require a change of the neutral hydrogen fraction of the order ∆χ HI ∼ 0.6 in a time ∆z ∼ 1, provided that the escape fraction does not increase dramatically over the same redshift interval.

The earliest generation of stars and black holes must have established an early 'Lyman-Werner' background (LWB) at high redshift, prior to the epoch of reionization. Because of the long mean free path of photons with energies hν < 13.6 eV, the LWB was nearly uniform. However, some variation in the LWB is expected due to the discrete nature of the sources, and their highly clustered spatial distribution. In this paper, we compute the probability distribution function (PDF) of the LW flux that irradiates dark matter (DM) haloes collapsing at high redshift (z ≈ 10). Our model accounts for (i) the clustering of DM haloes, (ii) Poisson fluctuations in the number of corresponding star-forming galaxies and (iii) scatter in the LW luminosity produced by haloes of a given mass (calibrated using local observations). We find that >99 per cent of the DM haloes are illuminated by an LW flux within a factor of 2 of the global mean value. However, a small fraction, ∼10 −8 to 10 −6 , of DM haloes with virial temperatures T vir 10 4 K have a close luminous neighbour within 10 kpc, and are exposed to an LW flux exceeding the global mean by a factor of >20, or to J 21,LW > 10 3 (in units of 10 −21 erg s −1 Hz −1 sr −1 cm −2 ). This large LW flux can photodissociate H 2 molecules in the gas collapsing due to atomic cooling in these haloes, and prevent its further cooling and fragmentation. Such close halo pairs therefore provide possible sites in which primordial gas clouds collapse directly into massive black holes (M BH ≈ 10 4−6 M ), and subsequently grow into supermassive (M BH 10 9 M ) black holes by z ≈ 6.

We present a new flexible Bayesian framework for directly inferring the fraction of neutral hydrogen in the intergalactic medium (IGM) during the Epoch of Reionization (EoR, z ∼ 6 − 10) from detections and non-detections of Lyman Alpha (Lyα) emission from Lyman Break galaxies (LBGs). Our framework combines sophisticated reionization simulations with empirical models of the interstellar medium (ISM) radiative transfer effects on Lyα. We assert that the Lyα line profile emerging from the ISM has an important impact on the resulting transmission of photons through the IGM, and that these line profiles depend on galaxy properties. We model this effect by considering the peak velocity offset of Lyα lines from host galaxies' systemic redshifts, which are empirically correlated with UV luminosity and redshift (or halo mass at fixed redshift). We use our framework on the sample of LBGs presented in Pentericci et al. (2014) and infer a global neutral fraction at z ∼ 7 of x hi = 0.59 +0.11 −0.15 , consistent with other robust probes of the EoR and confirming reionization is on-going ∼ 700 Myr after the Big Bang. We show that using the full distribution of Lyα equivalent width detections and upper limits from LBGs places tighter constraints on the evolving IGM than the standard Lyα emitter fraction, and that larger samples are within reach of deep spectroscopic surveys of gravitationally lensed fields and JWST NIRSpec.