Erschienen in:
The Astrophysical Journal, 884 (2019) 2, Seite 154
Sprache:
Nicht zu entscheiden
DOI:
10.3847/1538-4357/ab44aa
ISSN:
1538-4357;
0004-637X
Entstehung:
Anmerkungen:
Beschreibung:
<jats:title>Abstract</jats:title>
<jats:p>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 <jats:italic>z</jats:italic>
<jats:sub>CO</jats:sub> = 3.329, illustrating the risk of misidentifying shorter wavelength counterparts. The optical-to-millimeter spectral energy distribution (SED) favors a gray <jats:italic>λ</jats:italic>
<jats:sup>−0.4</jats:sup> 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/submillimeter/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 signal-to-noise ratio ∼ 3 measurements in stacked IRAC 3.6+4.5, ultradeep SCUBA2 850 <jats:italic>μ</jats:italic>m, and VLA 3 GHz, indicating the source is real. The SED is robustly reproduced by a massive <jats:italic>M</jats:italic>* = 10<jats:sup>10.8</jats:sup>
<jats:italic>M</jats:italic>
<jats:sub>⊙</jats:sub> and <jats:italic>M</jats:italic>
<jats:sub>gas</jats:sub> = 10<jats:sup>11</jats:sup>
<jats:italic>M</jats:italic>
<jats:sub>⊙</jats:sub>, highly obscured <jats:italic>A</jats:italic>
<jats:sub>
<jats:italic>V</jats:italic>
</jats:sub> ∼ 4, star-forming SFR ∼ 300 <jats:italic>M</jats:italic>
<jats:sub>⊙</jats:sub> yr<jats:sup>−1</jats:sup> galaxy at redshift <jats:italic>z</jats:italic> = 5.5 ± 1.1. The ultrasmall 8 arcmin<jats:sup>2</jats:sup> survey area implies a large yet uncertain contribution to the cosmic star formation rate density CSFRD(<jats:italic>z</jats:italic> = 5) ∼ 0.9 × 10<jats:sup>−2</jats:sup>
<jats:italic>M</jats:italic>
<jats:sub>⊙</jats:sub> yr<jats:sup>−1</jats:sup> Mpc<jats:sup>−3</jats:sup>, comparable to all ultraviolet-selected galaxies combined. These results indicate the existence of a prominent population of DSFGs at <jats:italic>z</jats:italic> > 4, below the typical detection limit of bright galaxies found in single-dish submillimeter surveys, but with larger space densities ∼3 × 10<jats:sup>−5</jats:sup> Mpc<jats:sup>−3</jats:sup>, higher duty cycles of 50%–100%, contributing more to the CSFRD, and potentially dominating the high-mass galaxy stellar mass function.</jats:p>