The ALMA Spectroscopic Survey in the Hubble Ultra Deep Field: Molecular Gas Reservoirs in High-redshift Galaxies

Journal
Date Issued
2016
Author(s)
•
Walter, Fabian
•
Aravena, Manuel
•
Carilli, Chris
•
Bouwens, Rychard
•
da Cunha, Elisabete
•
Daddi, Emanuele
•
Elbaz, David
•
Riechers, Dominik
•
Smail, Ian
•
Swinbank, Mark
•
Weiss, Axel
•
Bacon, Roland
•
Bauer, Franz
•
Bell, Eric F.
•
Bertoldi, Frank
•
Chapman, Scott
•
Colina, Luis
•
Cortes, Paulo C.
•
Cox, Pierre
•
Gónzalez-López, Jorge
•
Inami, Hanae
•
Ivison, Rob
•
Hodge, Jacqueline
•
Karim, Alex
•
Magnelli, Benjamin
•
Ota, Kazuaki
•
Popping, Gergö
•
Rix, Hans-Walter
•
Sargent, Mark
•
•
van der Werf, Paul
DOI
Abstract
We study the molecular gas properties of high-z galaxies observed in the ALMA Spectroscopic Survey (ASPECS) that targets an ∼1 arcmin2 region in the Hubble Ultra Deep Field (UDF), a blind survey of CO emission (tracing molecular gas) in the 3 and 1 mm bands. Of a total of 1302 galaxies in the field, 56 have spectroscopic redshifts and correspondingly well-defined physical properties. Among these, 11 have infrared luminosities {L}{IR}\gt {10}11 {L}☉ , I.e., a detection in CO emission was expected. Out of these, 7 are detected at various significance in CO, and 4 are undetected in CO emission. In the CO-detected sources, we find CO excitation conditions that are lower than those typically found in starburst/sub-mm galaxy/QSO environments. We use the CO luminosities (including limits for non-detections) to derive molecular gas masses. We discuss our findings in the context of previous molecular gas observations at high redshift (star formation law, gas depletion times, gas fractions): the CO-detected galaxies in the UDF tend to reside on the low-{L}{IR} envelope of the scatter in the {L}{IR}{--}{L}{CO}\prime relation, but exceptions exist. For the CO-detected sources, we find an average depletion time of ∼1 Gyr, with significant scatter. The average molecular-to-stellar mass ratio ({M}{{H}2}/M *) is consistent with earlier measurements of main-sequence galaxies at these redshifts, and again shows large variations among sources. In some cases, we also measure dust continuum emission. On average, the dust-based estimates of the molecular gas are a factor ∼2-5× smaller than those based on CO. When we account for detections as well as non-detections, we find large diversity in the molecular gas properties of the high-redshift galaxies covered by ASPECS.
Volume
833
Issue
1
Start page
70
Uri
Url
Issn Identifier
0004-637X
Ads BibCode
2016ApJ...833...70D
Rights
open.access
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