The Astrophysical Journal (Jan 2024)
An ALMA Spectroscopic Survey of the Brightest Submillimeter Galaxies in the SCUBA-2-COSMOS Field (AS2COSPEC): Physical Properties of z = 2–5 Ultra- and Hyperluminous Infrared Galaxies
Abstract
We report the physical properties of the 18 brightest ( S _870 _μ _m = 12.4–19.2 mJy) and not strongly lensed 870 μ m–selected dusty star-forming galaxies (DSFGs), also known as submillimeter galaxies (SMGs), in the COSMOS field. This sample is part of an ALMA band 3 spectroscopic survey (AS2COSPEC), and spectroscopic redshifts are measured in 17 of them at z = 2–5. We perform spectral energy distribution analyses and deduce a median total infrared luminosity of L _IR = (1.3 ± 0.1) × 10 ^13 L _⊙ , infrared-based star formation rate (SFR) of SFR _IR = 1390 ± 150 M _⊙ yr ^−1 , stellar mass of M _* = (1.4 ± 0.6) × 10 ^11 M _⊙ , dust mass of M _dust = (3.7 ± 0.5) × 10 ^9 M _⊙ , and molecular gas mass of M _gas = ( α _CO /0.8)(1.2 ± 0.1) × 10 ^11 M _⊙ , suggesting that they are one of the most massive, ISM-enriched, and actively star-forming systems at z = 2–5. In addition, compared to less massive and less active galaxies at similar epochs, SMGs have comparable gas fractions; however, they have a much shorter depletion time, possibly caused by more active dynamical interactions. We determine a median dust emissivity index of β = 2.1 ± 0.1 for our sample, and by combining our results with those from other DSFG samples, we find no correlation of β with redshift or infrared luminosity, indicating similar dust grain compositions across cosmic time for infrared luminous galaxies. We also find that AS2COSPEC SMGs have one of the highest dust-to-stellar mass ratios, with a median of 0.02 ± 0.01, significantly higher than model predictions, possibly due to too-strong active galactic nucleus feedback implemented in the model. Finally, our complete and uniform survey enables us to put constraints on the most massive end of the dust and molecular gas mass functions.
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