Cosmic Reionization On Computers: The Faint End of the Galaxy Luminosity Function

TL;DR

This paper uses cosmological simulations to analyze the faint end of galaxy UV luminosity functions during reionization, showing that a Schechter function with a variable magnitude cut fits well and that an analytical model can describe the results with adjustments.

Contribution

It demonstrates that a Schechter function with a magnitude cut between -12 and -14 accurately models simulated galaxy luminosity functions at high redshift.

Findings

Schechter function fits simulated luminosity functions well

Magnitude cut varies mildly with redshift

Analytical reionization model aligns with simulations when escape fraction evolution is included

Abstract

Using numerical cosmological simulations completed under the "Cosmic Reionization On Computers" (CROC) project, I explore theoretical predictions for the faint end of the galaxy UV luminosity functions at $z\geq 6$. A commonly used Schechter function approximation with the magnitude cut at $M_{\rm CUT}\sim-13$ provides a reasonable fit to the actual luminosity function of simulated galaxies. When the Schechter functional form is forced on the luminosity functions from the simulations, the magnitude cut $M_{\rm CUT}$ is found to vary between $-12$ and $-14$ with a mild redshift dependence. An analytical model of reionization from Madau, Haardt & Rees (1997), as used by Robertson et al. (2015), provides a good description of the simulated results, but only if the redshift dependence of the effective escape fraction (induced by physical processes not captured by the Madau, Haardt & Rees model) is accounted for.