Gas and galaxies at z ~ 3.

Abstract

In this thesis we present analyses of z ~ 3 star-forming Lyman break galaxy and Lyman-alpha emitter populations.
Additionally, we use QSO sightlines to probe the properties of gas around the LBGs. The observed star-forming galaxy sample is based on spectroscopic redshift data taken from a combination of the VLT LBG Redshift Survey (VLRS) data and Keck LRIS observations in fields centred on bright background QSOs. We compare these data with results from a GIMIC hydrodynamical simulation. We first estimate the auto-correlation function of simulated galaxies and compare these results with the observed Keck+VLRS correlation functions. We find that the observed galaxy real-space auto-correlation function is more consistent with that measured for simulated M⋆ ≥ 10^9 h^−1 M⊙ galaxies than lower mass galaxies.

We then calculate the cross correlation of galaxies with Ly-alpha absorption in QSO sightlines in both our observed and simulated datasets. We check near star-forming galaxies in both data and simulations for the existence of the transmission spike which previous authors have claimed to be indicative of the effects of star-formation feedback on the IGM. No detection of such a spike is seen in the galaxy-gas correlation function in the combined VLRS+Keck data. The simulated cross-correlation function also shows comparable neutral gas densities around galaxies as seen in the observations. The Ly-alpha auto- and cross-correlation functions in the GIMIC simulations, appear to show infall smaller than implied by the predicted infall parameter of
β_Lyα ≈ 1.3 (McDonald et al.). There is a possibility
that the reduced infall may be due to the galaxy wide outflows implemented in the simulations.


We present the Lyman-α luminosity functions and two-point clustering correlation functions of Lyα emitters (LAEs) at z = 3.1. We obtain a photometric sample of ~500 LAE candidates from 5 fields based on deep Subaru Suprime-Cam imaging data and a spectroscopic sample of 62 confirmed LAEs in 3 of our 5 fields from VLT VIMOS spectroscopy.
We find that our narrowband Lyα luminosity function is in agreement with Ouchi et al. (2008) and is higher than for Gronwall et al. (2007). We estimate the R-band continuum luminosity functions of our sample of LAEs. Our 1700 Å continuum magnitude (auto) LAE luminosity function appears similar to that of Gronwall et al.(2007) with a relatively high number density of LAE being detected at bright magnitudes. We compare LAE and LBG R-band continuum luminosity functions and find that the LAE luminosity function at R < 25.5 amounts to only ~30 % of the density of the LBG luminosity function. Nevertheless, most of LAE still lie at the faint end of the LBG luminosity function.
Finally, by comparing the 3-D LAE and LBG clustering amplitudes as estimated from the angular correlation function, we find a lower r_0 for LAE than for the LBGs.
We measure a correlation length in the range of r_0 = 1.8-3.1 h^-1 Mpc and a bias in the range of b = 1.4-2.3 for LAEs. Even the highest LAE r_0 value is significantly lower than that of LBGs. The average LAE dark matter halo mass inferred from clustering is in the range of 10^-10^ h^ M⊙. The lower correlation length leads to the lower halo masses.
Our results show that the LAE population is dominated by galaxies fainter than those traditionally selected via the Lyman Break method. It is possible that the LAE population may simply be a faint subset of the LBG selection and our results, in terms of both the luminosity function and clustering, are consistent with this picture.