Probing Stellar Populations at z ~ 7 - 8

TL;DR

This study uses deep near-infrared data from Hubble's WFC3 to identify and analyze galaxies at redshifts 6.3 to 8.6, revealing bluer UV colors, lower stellar masses, and implications for cosmic reionization.

Contribution

First deep near-infrared survey at z ~ 7-8 with 31 galaxy detections, showing evolution in galaxy properties and their role in reionization.

Findings

Galaxies at z ~ 7-8 have extremely blue UV colors.

Stellar masses are lower than at z ~ 3-6.

UV luminosity density may sustain reionization.

Abstract

In this proceeding we present the results from a study of very high-redshift galaxies with the newly commissioned Wide Field Camera 3 on the Hubble Space Telescope. With the deepest near-infrared data ever taken, we discovered 31 galaxies at 6.3 < z < 8.6. The rest-frame ultraviolet (UV) colors of these galaxies are extremely blue, showing significant (> 4 sigma) evolution from z ~ 3, over only 1 Gyr of cosmic time. While we cannot yet diagnose the exact cause of the bluer colors, it appears a low dust content is the primary factor. The stellar masses of these galaxies are less than comparably selected galaxies at 3 < z < 6, highlighting evolution in the stellar mass of characteristic (L*) galaxies with redshift. Lastly, the measured rest-UV luminosity density of galaxies in our sample seems sufficient to sustain reionization at z ~ 7 when we account for the likely contribution from galaxies below our magnitude limit.