2019/05/31 by Christina C. Williams, Ivo Labbe, Justin Spilker +7 · 6 citations
Physics and Astronomy · #Astronomy and Astrophysical Research #Galaxies: Formation, Evolution, Phenomena #Radio Astronomy Observations and Technology #astro-ph.GA
paper · pdf · doi:10.3847/1538-4357/ab44aa
Accepted for publication in ApJ. 2 galaxies, too many pages, 8 figures, 2 tables
openalex created_date 2019/06/07 · arxiv created 2019/09/23 · openalex publication_date 2019/10/20 · arxiv updated 2019/11/06 · openalex updated_date 2026/08/05
We report the serendipitous detection of two 3 mm continuum sources found in deep ALMA Band 3 observations to study intermediate redshift galaxies in the COSMOS field. One is near a foreground galaxy at 1.3", but is a previously unknown dust-obscured star-forming galaxy (DSFG) at probable zCO=3.329, illustrating the risk of misidentifying shorter wavelength counterparts. The optical-to-mm spectral energy distribution (SED) favors a grey λ-0.4 attenuation curve and results in significantly larger stellar mass and SFR compared to a Calzetti starburst law, suggesting caution when relating progenitors and descendants based on these quantities. The other source is missing from all previous optical/near-infrared/sub-mm/radio catalogs ("ALMA-only"), and remains undetected even in stacked ultradeep optical (>29.6 AB) and near-infrared (>27.9 AB) images. Using the ALMA position as a prior reveals faint SNR∼3 measurements in stacked IRAC 3.6+4.5, ultradeep SCUBA2 850μm, and VLA 3GHz, indicating the source is real. The SED is robustly reproduced by a massive M^*=1010.8M_\odot and Mgas=1011M_\odot, highly obscured AV∼4, star forming SFR∼300 M\odotyr-1 galaxy at redshift z=5.5±1.1. The ultrasmall 8 arcmin2 survey area implies a large yet uncertain contribution to the cosmic star formation rate density CSFRD(z=5) ∼0.9×10-2 M\odot yr-1 Mpc-3, comparable to all ultraviolet-selected galaxies combined. These results indicate the existence of a prominent population of DSFGs at z>4, below the typical detection limit of bright galaxies found in single-dish sub-mm surveys, but with larger space densities ∼3 × 10-5 Mpc-3, higher duty cycles 50-100%, contributing more to the CSFRD, and potentially dominating the high-mass galaxy stellar mass function.