Extensive Lensing Survey of Optical and Near-Infrared Dark Objects (El Sonido): HST H-Faint Galaxies behind 101 Lensing Clusters

Abstract

We present a Spitzer/IRAC survey of H-faint ($H_{160}\gtrsim 26.4$, $<5\ddot{I}ƒ$) sources in 101 lensing cluster fields. Across a CANDELS/Wide-like survey area of $\sim$648 arcmin${}^2$ (effectively $\sim$221 arcmin${}^2$ in the source plane), we have securely discovered 53 sources in the IRAC Channel-2 band (CH2, 4.5 $\hat{\mathrm{I}}¼\mathrm{m}$; median CH2$=22.46\pm 0.11$ AB mag) that lack robust HST/WFC3-IR F160W counterparts. The most remarkable source in our sample, namely ES-009 in the field of Abell 2813, is the brightest H-faint galaxy at 4.5 $\hat{\mathrm{I}}¼\mathrm{m}$ known so far ($CH2=20.48\pm 0.03$ AB mag). We show that the H-faint sources in our sample are massive (median $M_{\mathrm{star}}=10^{10.3\pm 0.3}$ $M_{\odot }$), star-forming (median star formation rate $=100_{-40}^{+60}$ $M_{\odot }$yr${}^{-1}$) and dust-obscured ($A_V=2.6\pm 0.3$) galaxies around a median photometric redshift of $z=3.9\pm 0.4$. The stellar continua of 14 H-faint galaxies can be resolved in the CH2 band, suggesting a median circularized effective radius ($R_{\mathrm{e},\mathrm{circ}}$; lensing corrected) of $1.9\pm 0.2$ kpc and $<1.5$ kpc for the resolved and whole samples, respectively. This is consistent with the sizes of massive unobscured galaxies at $z\sim 4$, indicating that H-faint galaxies represent the dusty tail of the distribution of a wider galaxy population. Comparing with the ALMA dust continuum sizes of similar galaxies reported previously, we conclude that the heavy dust obscuration in H-faint galaxies is related to the compactness of both stellar and dust continua ($R_{\mathrm{e},\mathrm{circ}}\sim 1$ kpc). These H-faint galaxies make up $16_{-7}^{+13}$% of the galaxies in the stellar mass range of $10^{10}-10^{11.2}$ $M_{\odot }$ at $z=3\sim 5$, contributing to $8_{-4}^{+8}$% of the cosmic star formation rate density in this epoch and likely tracing the early phase of massive galaxy formation.

26 pages, 10 figures, 3 tables. Accepted for publication in ApJ