2mm Observations and the Search for High-Redshift Dusty Star-forming Galaxies. (arXiv:2305.17167v1 [astro-ph.GA])
<a href="http://arxiv.org/find/astro-ph/1/au:+Cowie_L/0/1/0/all/0/1">L.L. Cowie</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Barger_A/0/1/0/all/0/1">A.J. Barger</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Bauer_F/0/1/0/all/0/1">F.E. Bauer</a>
Finding high-redshift (z>>4) dusty star-forming galaxies is extremely
challenging. It has recently been suggested that millimeter selections may be
the best approach, since the negative K-correction makes galaxies at a given
far-infrared (FIR) luminosity brighter at z>4 than those at z=2-3. Here we
analyze this issue using a deep ALMA 2mm sample obtained by targeting ALMA
870um priors (these priors were the result of targeting SCUBA-2 850um sources)
in the GOODS-S. We construct the prior-based 2mm galaxy number counts and
compare them with published blank field-based 2mm counts, finding good
agreement down to 0.2mJy. Only a fraction of the current 2mm extragalactic
background light is resolved, and we estimate what observational depths may be
needed to resolve it fully. By complementing the 2mm ALMA data with a deep
SCUBA-2 450um sample in the GOODS-S, we exploit the steep gradient with
redshift of the 2mm to 450um flux density ratio to estimate redshifts for these
galaxies without spectroscopic or robust optical/near-infrared photometric
redshifts. Our observations measure galaxies with star formation rates in
excess of 250 solar masses per year. For these galaxies, the star formation
rate densities fall by a factor of 9 from z=2-3 to z=5-6.
Finding high-redshift (z>>4) dusty star-forming galaxies is extremely
challenging. It has recently been suggested that millimeter selections may be
the best approach, since the negative K-correction makes galaxies at a given
far-infrared (FIR) luminosity brighter at z>4 than those at z=2-3. Here we
analyze this issue using a deep ALMA 2mm sample obtained by targeting ALMA
870um priors (these priors were the result of targeting SCUBA-2 850um sources)
in the GOODS-S. We construct the prior-based 2mm galaxy number counts and
compare them with published blank field-based 2mm counts, finding good
agreement down to 0.2mJy. Only a fraction of the current 2mm extragalactic
background light is resolved, and we estimate what observational depths may be
needed to resolve it fully. By complementing the 2mm ALMA data with a deep
SCUBA-2 450um sample in the GOODS-S, we exploit the steep gradient with
redshift of the 2mm to 450um flux density ratio to estimate redshifts for these
galaxies without spectroscopic or robust optical/near-infrared photometric
redshifts. Our observations measure galaxies with star formation rates in
excess of 250 solar masses per year. For these galaxies, the star formation
rate densities fall by a factor of 9 from z=2-3 to z=5-6.
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