Luminous and High Stellar Mass Candidate Galaxies at z ~ 8 Discovered in CANDELS

TL;DR

This study identifies luminous, high-mass galaxy candidates at redshift around 8 using the CANDELS survey, providing new insights into galaxy evolution, luminosity functions, and stellar mass distribution in the early universe.

Contribution

It reports the discovery of the brightest and most massive z~8 galaxy candidates, constrains the bright-end of the UV luminosity function, and measures the high-mass end of the stellar mass function at this epoch.

Findings

Detection of two galaxies brighter than previous records.

First individual Spitzer detections of z~8 galaxies.

Evidence for a higher number density of luminous and massive galaxies than expected.

Abstract

One key goal of the Hubble Space Telescope Cosmic Assembly Near-Infrared Deep Extragalactic Legacy Survey is to track galaxy evolution back to z ~ 8. Its two-tiered "wide and deep" strategy bridges significant gaps in existing near-infrared surveys. Here we report on z ~ 8 galaxy candidates selected as F105W-band dropouts in one of its deep fields, which covers 50.1 square arcmin to 4 ks depth in each of three near-infrared bands in the Great Observatories Origins Deep Survey southern field. Two of our candidates have J<26.2 mag, and are > 1 mag brighter than any previously known F105W-dropouts. We derive constraints on the bright-end of the rest-frame ultraviolet luminosity function of galaxies at z ~ 8, and show that the number density of such very bright objects is higher than expected from the previous Schechter luminosity function estimates at this redshift. Another two candidates are securely detected in Spitzer Infrared Array Camera images, which are the first such individual detections at z ~ 8. Their derived stellar masses are on the order of a few x 10^9 M_sun, from which we obtain the first measurement of the high-mass end of the galaxy stellar mass function at z ~ 8. The high number density of very luminous and very massive galaxies at z ~ 8, if real, could imply a large stellar-to-halo mass ratio and an efficient conversion of baryons to stars at such an early time.