The UV-continuum properties of Ly alpha selected galaxies at z=6.5

TL;DR

This study presents the first deep space-based near-infrared observations of z=6.5 galaxies with Ly alpha emission, revealing their properties and prevalence, and comparing them to lower-redshift counterparts.

Contribution

It provides the first uniform, deep near-infrared continuum measurements of z=6.5 Ly alpha galaxies, establishing their sizes, star formation rates, and Ly alpha line properties.

Findings

Ly alpha emission is present in about 24% of galaxies with M_AB(1350 A) < -20.

Galaxies are small (<1 kpc) with star formation rates around 10 Msun/yr.

Little evidence of Ly alpha line destruction at z=6.5.

Abstract

We report the first space-based very deep near-infrared continuum observations of a uniform sample of z = 6.5 galaxies with log(L(L_alpha)) = 42.5 - 43 erg/s selected from narrow-band line searches and with spectroscopically confirmed Ly alpha emission. The 1.4 micron HST WFC3 observations are deep enough (AB(1 sigma) = 28.75) to measure individual continuum magnitudes at this redshift for all of the objects. We compare the results with continuum-selected samples at the same redshift and find that Ly alpha emission is present in 24% of all galaxies with M_AB(1350 A) < -20 at z = 6.5. The error in this quantity is dominated by systematic uncertainties, which could be as large as multiplicative factors of three. The Ly alpha galaxies are extended but small (size < 1 kpc), and have star formation rates of approximately 10 Msun/yr. We find a mean L(Ly alpha)/(nu L_nu) at 1400A of 0.08, with the seven objects showing a range from 0.026 to 0.26, implying that there is little sign of destruction of the Ly alpha line. All of the properties of the z = 6.5 sample appear to be very similar to those of Ly alpha emitters at lower redshifts.