The faint end of the UV luminosity function at $0.4 < z < 0.7$ from the Hubble Frontier Fields

TL;DR

This paper uses HFF lensing and new F225W imaging to push the rest-frame UV LF measurements to very faint magnitudes at intermediate redshift, reaching $M_{UV} \sim -13.5$ at $z \sim 0.55$. It identifies 152 faint galaxies in Abell 2744 with $-19.5 < M_{UV} < -12.1$ over $0.4<z<0.7$, employing hybrid photometric-spectroscopic redshifts. A maximum-likelihood fit to a Schechter form is performed, incorporating a curvature parameter $\delta$ to test a faint-end turnover and applying a $50\%$ completeness cut. The inferred faint-end slope is $\alpha = -1.324^{+0.072}_{-0.074}$, and a turnover brighter than $M_{UV} = -15.5$ is ruled out at $3\sigma$, underscoring the significance of the faint galaxy population for cosmic star formation at $z \sim 0.55$.

Abstract

By extending the Hubble Frontier Fields (HFF) observations to the F225W band using HST WFC3/UVIS, we measure the rest-frame UV luminosity function (LF) of galaxies at $0.4 < z < 0.7$, pushing into the low-luminosity galaxy regime. In this first paper of a series, we describe the HST Cycle-27 GO-15940 F225W observations and data reduction, and present a corresponding catalog for the Abell 2744 field, which is the most data-rich HFF cluster field. Combining deep Near-UV imaging and the high magnification from strong gravitational lensing of the foreground cluster, we identify 152 faint galaxies with $-19.5 < M_{UV} < -12.1$ at $0.4 < z < 0.7$ through hybrid photometric-spectroscopic redshift selection from the Abell 2744 F225W catalog. Using a sample defined by a $50\%$ completeness cut and applying the maximum likelihood estimation, we derive the best-fit Schechter parameters for the UV LF at $z \sim 0.55$ down to $M_\text{UV} < -13.5$ mag, including a faint-end slope of $α= -1.324^{+0.072}_{-0.074}$. We incorporate a curvature parameter $δ$ in parameter estimation to account for a possible turn-over at the faint end of the UV LF, leveraging the exceedingly low luminosities probed by our sample. Our results rule out a turn-over brighter than $M_{UV} = -15.5$ at the $3σ$ confidence level.