A Systematic Search for Lensed High-Redshift Galaxies in HST Images of MACS Clusters

TL;DR

This study systematically searches for high-redshift lensed galaxies in HST images of MACS clusters, identifying candidates at redshifts up to 9 and demonstrating the effectiveness of limited-band photometry for such detections.

Contribution

It introduces a method for identifying high-redshift galaxies using shallow HST images and four broad-band filters, including a prior for dust extinction and bias analysis.

Findings

Identified 20 galaxies at redshifts 7 to 9.

Detected over 100 potential lower-redshift interlopers.

Showed four filters suffice for promising high-redshift candidate selection.

Abstract

We present the results of a 135-arcmin$^2$ search for high-redshift galaxies lensed by 29 clusters from the MAssive Cluster and extended MAssive Cluster Surveys (MACS and eMACS). We use relatively shallow images obtained with the Hubble Space Telescope in four passbands, namely, F606W, F814W, F110W, and F140W. We identify 130 F814W dropouts as candidates for galaxies at $z \le 6$. In order to fit the available broad-band photometry to galaxy spectral energy distribution (SED) templates, we develop a prior for the level of dust extinction at various redshifts. We also investigate the systematic biases incurred by the use of SED-fit software. The fits we obtain yield an estimate of 20 Lyman-break galaxies with photometric redshifts from $z \sim 7$ to 9. In addition, our survey has identified over 100 candidates with a significant probability of being lower-redshift ($z \sim 2$) interlopers. We conclude that even as few as four broad-band filters -- when combined with fitting the SEDs -- are capable of isolating promising objects. Such surveys thus allow one both to probe the bright end ($M_{1500} \le -19$) of the high-redshift UV luminosity function and to identify candidate massive evolved galaxies at lower redshifts.