IMPACT OF COSMIC VARIANCE ON THE GALAXY–HALO CONNECTION FOR Lyα EMITTERS

Abstract

ABSTRACT In this paper we study the impact of cosmic variance and observational uncertainties in constraining the mass and occupation fraction, f occ -->?> , of dark matter (DM) halos hosting Lyα-emitting galaxies (LAEs) at high redshift. To this end, we construct mock catalogs from an N-body simulation to match the typical size of observed fields at z = 3.1 ( ∼ 1 deg 2 -->?> ). In our model a DM halo with mass in the range M min < M h < M max -->?> can only host one detectable LAE at most. We proceed to explore the parameter space determined by M min -->?> , M max -->?> , and f occ -->?> with a Markov Chain Monte Carlo algorithm using the angular correlation function and the LAEs’ number density as observational constraints. We find that the preferred minimum and maximum masses in our model span a wide range 10 10.0 h − 1 M ⊙ ≤ M min ≤ 10 11.1 h − 1 M ⊙ -->?> , 10 11.0 h − 1 M ⊙ ≤ M max ≤ 10 13.0 h − 1 M ⊙ , -->?> followed by a wide range in the occupation fraction 0.02 ≤ f occ ≤ 0.30 -->?> . As a consequence, the median mass, M 50, of all the consistent models has a large uncertainty M 50 = 3.16 − 2.37 + 9.34 × 10 10 -->?> h − 1 M ⊙ -->?> . However, we find that the same individual models have a relatively tight 1 &sgr; -->?> scatter around the median mass Δ M 1 &sgr; = 0.55 − 0.31 + 0.11 -->?> dex. We are also able to show that f occ -->?> is uniquely determined by M min -->?> , regardless of M max -->?> . We argue that upcoming large surveys covering at least 25 deg2 should be able to put tighter constraints on M min -->?> and f occ -->?> through the LAE number density distribution width constructed over several fields of ∼1 deg2.