Extensive Lensing Survey of Optical and Near-infrared Dark Objects (El Sonido): HST H-faint Galaxies behind 101 Lensing Clusters
Abstract
Abstract We present a Spitzer/IRAC survey of H -faint ( H 160 ≳ 26.4, < 5 σ ) sources in 101 lensing cluster fields. Across a CANDELS/Wide-like survey area of ∼648 arcmin 2 (effectively ∼221 arcmin 2 in the source plane), we have securely discovered 53 sources in the IRAC Channel-2 band (CH2, 4.5 μ m; median CH2 = 22.46 ± 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 μ m known so far (CH2 = 20.48 ± 0.03 AB mag). We show that the H -faint sources in our sample are massive (median M star = 10 10.3±0.3 M ⊙ ), star-forming (median star formation rate = 100 − 40 + 60 M ⊙ yr −1 ), and dust-obscured ( A V = 2.6 ± 0.3) galaxies around a median photometric redshift of z = 3.9 ± 0.4. The stellar continua of 14 H -faint galaxies can be resolved in the CH2 band, suggesting a median circularized effective radius ( R e,circ ; lensing corrected) of 1.9 ± 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 ∼ 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 e,circ ∼ 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 ⊙ at z = 3 ∼ 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.
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