The physical properties and detectability of reionization-epoch galaxies

Abstract

We present predictions drawn from cosmological hydrodynamic simulations for the physical, photometric and emission line properties of galaxies present during the latter stages of reionization from z=9-6. We find significant numbers of galaxies that have stellar masses exceeding 10^8 Mo during this epoch, with metallicities exceeding one-thirtieth solar. Far from primeval first-star objects,these objects are likely to have reionized their infall regions prior to z=9, are dominated by atomic rather than molecular cooling, and are not expected to be forming Population III stars. Galaxies exhibit a slowly evolving comoving autocorrelation length from z=9-6, continuing a trend seen at lower redshifts in which the rapidly dropping bias counteracts the rapidly increasing matter clustering. These sources can be marginally detected using current instruments, but modest increases in sensitivity or survey area would yield significantly increased samples. We compare to current observations of the z~6 rest-UV and Ly-alpha line luminosity functions, and find good agreement. We also compare with the z~7 object observed by Egami et al., and find that such systems are ubiquitous in our simulations. The intrinsic Ly-alpha luminosity function evolves slowly from z=9-6, meaning that it should also be possible to detect these objects with upcoming narrow band surveys such as DAzLE. We make predictions for near-IR surveys with JWST, and show that while a high density of sources will be found, Population III objects may remain elusive. We present and compare simulations with several recipes for superwind feedback, and show that while our broad conclusions are insensitive to this choice, a feedback model based on momentum-driven winds is favored in comparisons with available data. (abridged)