Galaxy stellar mass functions from z similar to 10 to z similar to 6 using the deepest spitzer/infrared array camera data: no significant evolution in the stellar-to-halo mass ratio of galaxies in the first gigayear of cosmic time

Abstract

We present new stellar mass functions at z similar to 6, z similar to 7, z similar to 8, z similar to 9 and, for the first time, z similar to 10, constructed from similar to 800 Lyman-break galaxies previously identified over the eXtreme Deep Field and Hubble Ultra-Deep Field parallel fields and the five Cosmic Assembly Near-infrared Deep Extragalactic Legacy Survey fields. Our study is distinctive due to (1) the much deeper (similar to 200 hr) wide-area Spitzer/Infrared Array Camera (IRAC) imaging at 3.6 mu m and 4.5 mu m from the Great Observatories Origins Deep Survey Re-ionization Era Wide-area Treasury from Spitzer program (GREATS) and (2) consideration of z similar to 6-10 sources over a 3 x larger area than those of previous Hubble Space Telescope+Spitzer studies. The Spitzer/IRAC data enable >=.2 rest-frame optical detections for an unprecedented 50% of galaxies down to a stellar mass limit of similar to 10(8) M-circle dot across all redshifts. Schechter fits to our volume densities suggest a combined evolution in the characteristic mass M* and normalization factor phi* between z similar to 6 and z similar to 8. The stellar mass density (SMD) increases by similar to 1000 x in the -500 Myr between z similar to 10 and z similar to 6, with indications of a steeper evolution between z similar to 10 and z similar to 8, similar to the previously reported trend of the star formation rate density. Strikingly, abundance matching to the Bolshoi-Planck simulation indicates halo mass densities evolving at approximately the same rate as the SMD between z similar to 10 and z similar to 4. Our results show that the stellar-to-halo mass ratios, a proxy for the star formation efficiency, do not change significantly over the huge stellar mass buildup occurred from z similar to 10 to z similar to 6, indicating that the assembly of stellar mass closely mirrors the buildup in halo mass in the first similar to 1 Gyr of cosmic history. The James Webb Space Telescope is poised to extend these results into the "first galaxy" epoch at z greater than or similar to 10.