The Nature of Emission-Line Galaxies in Hierarchical Cosmologies

We use a galaxy formation model to study the nature and evolution of emission line galaxies. In particular, we focus on the properties of Ly-alpha and H-alpha emitters, due to their many cosmological applications being considered for current and future observational studies. By combining a semianalytical model with a large N-body simulation we predict the clustering of Ly-alpha emitters. With increasing redshift, Ly-alpha emitters are found to trace progressively rarer, higher density regions of the Universe. We measure the clustering of Ly-alpha emitters by constructing mock catalogues of surveys finding a good agreement between the model and the observational measurements. Furthermore, we use the mock catalogues to study the sample variance of current and forthcoming Ly-alpha surveys. Current surveys should be extended significantly in solid angle to allow a robust measurement of the clustering of Ly-alpha emitters, particularly at z>8. On the other hand, future space-based galaxy surveys will map the galaxy distribution using H-alpha emitters or H-band selected galaxies at 0.5<z<2 to constrain the nature of the dark energy by measuring the large-scale structure of the Universe. Therefore, we investigate the abundance and clustering of galaxies found using these two selections. H-alpha emitters are found to avoid massive dark matter haloes, whereas H-band selected galaxies are found in the highest mass haloes. By using mock catalogues, we predict the effectiveness of measuring the large scale structure of the Universe for a range of survey configurations using both galaxy selections. Finally, we study the escape of Ly-alpha photons from galaxies using a Monte Carlo radiative transfer code. We simulate galactic outflows in a semianalytical model to study the physical properties of Ly-alpha emitters in a cosmological context. We find that the escape fraction of Ly-alpha emitters can vary greatly depending on the properties of the galaxies, although our results depend on the outflow model used. Our results suggest the need to consider additional physical effects to understand the observed properties of Ly-alpha emitters.