The Brightest Of Reionizing Galaxies Survey: Design and Preliminary Results

TL;DR

This paper reports the discovery of the brightest candidate galaxies at redshift around 8 from the BoRG survey, expanding the search area and identifying potential targets for spectroscopic follow-up.

Contribution

It presents the design and preliminary results of a wide-area survey for bright z~8 galaxies, identifying the brightest candidates to date and demonstrating the survey's effectiveness.

Findings

Identified four high-confidence z~8 galaxy candidates.

Candidates are approximately ten times brighter than previous known galaxies at similar redshift.

Survey area is more than twice as wide as previous WFC3 observations at z~8.

Abstract

We present the first results on the search for very bright (M_AB -21) galaxies at redshift z~8 from the Brightest of Reionizing Galaxies (BoRG) survey. BoRG is a Hubble Space Telescope Wide Field Camera 3 pure-parallel survey that is obtaining images on random lines of sight at high Galactic latitudes in four filters (F606W, F098M, F125W, F160W), with integration times optimized to identify galaxies at z>7.5 as F098M-dropouts. We discuss here results from a search area of approximately 130 arcmin^2 over 23 BoRG fields, complemented by six other pure-parallel WFC3 fields with similar filters. This new search area is more than two times wider than previous WFC3 observations at z~8. We identify four F098M-dropout candidates with high statistical confidence (detected at greater than 8sigma confidence in F125W). These sources are among the brightest candidates currently known at z~8 and approximately ten times brighter than the z=8.56 galaxy UDFy-38135539. They thus represent ideal targets for spectroscopic followup observations and could potentially lead to a redshift record, as our color selection includes objects up to z~9. However, the expected contamination rate of our sample is about 30% higher than typical searches for dropout galaxies in legacy fields, such as the GOODS and HUDF, where deeper data and additional optical filters are available to reject contaminants.