Impact of H2-based star formation model on the z ≥ 6 luminosity function and the ionizing photon budget for reionization

Abstract

We present the results of a numerical study examining the effect of an H2-based star formation (SF) model on the rest-frame UV luminosity function and star formation rate function (SFRF) of z ≥ 6 galaxies, and the implications for reionization. Using cosmological hydrodynamical simulations outfitted with an H2-SF model, we find good agreement with our previous results (non-H2 SF model) and observations at M uv ≤ -18. However, at M uv > -18, we find that the LF deviates from both our previous work and current observational extrapolations, producing significantly fewer low-luminosity galaxies and exhibiting additional turnover at the faint end. We constrain the redshift evolution of this turnover point using a modified Schechter function that includes additional terms to quantify the turnover magnitude (β) and subsequent slope (β). We find that evolves from (at z = 8) to -15.38 (z = 6), while β becomes shallower by Δβ = 0.22 during the same epoch. This occurs in an M uv range that will be observable by James Webb Space Telescope. By integrating the SFRF, we determine that even though the H2-SF model significantly reduces the number density of low-luminosity galaxies at M uv > -18, it does not suppress the total SFR density enough to affect the capability of SF to maintain reionization. © 2013. The American Astronomical Society. All rights reserved.