Scoville, N. and Sheth, K. and Aussel, H. and Vanden Bout, P. and Capak, P. and Bongiorno, A. and Casey, C. M. and Murchikova, L. and Koda, J. and Alvarez-Márquez, J. and Lee, N. and Laigle, C. and McCracken, H. J. and Ilbert, O. and Pope, A. and Sanders, D. and Chu, J. and Toft, S. and Ivison, R. J. and Manohar, S. (2016) ISM masses and the star formation law at Z = 1 to 6: ALMA observations of dust continuum in 145 galaxies in the COSMOS survey field. Astrophysical Journal, 820 (2). Art. No. 83. ISSN 0004-637X. http://resolver.caltech.edu/CaltechAUTHORS:20160316-073226088
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ALMA Cycle 2 observations of long-wavelength dust emission in 145 star-forming galaxies are used to probe the evolution of the star-forming interstellar medium (ISM). We also develop a physical basis and empirical calibration (with 72 low-z and z ~ 2 galaxies) for using the dust continuum as a quantitative probe of ISM masses. The galaxies with the highest star formation rates (SFRs) at <z>= 2.2 and 4.4 have gas masses up to 100 times that of the Milky Way and gas mass fractions reaching 50%–80%, i.e., gas masses 1-4× their stellar masses. We find a single high-z star formation law: SFR = 35 M^(0.89)_(mol) x (1 + z)^(0.95)_(z=2) x (sSFR)^(0.23)_(MS) M⊙yr^(−1)—an approximately linear dependence on the ISM mass and an increased star formation efficiency per unit gas mass at higher redshift. Galaxies above the main sequence (MS) have larger gas masses but are converting their ISM into stars on a timescale only slightly shorter than those on the MS; thus, these "starbursts" are largely the result of having greatly increased gas masses rather than an increased efficiency of converting gas to stars. At z > 1, the entire population of star-forming galaxies has ~2–5 times shorter gas depletion times than low-z galaxies. These shorter depletion times indicate a different mode of star formation in the early universe—most likely dynamically driven by compressive, high-dispersion gas motions—a natural consequence of the high gas accretion rates.
|Additional Information:||© 2016 The American Astronomical Society. Received 2015 May 7; accepted 2016 February 10; published 2016 March 22. We thank Zara Scoville for proof reading the manuscript and Sue Madden for suggesting use of the SPIRE fluxes for calibration. This paper makes use of the following ALMA data: ADS/JAO.ALMA# 2013.1.00034.S. This paper makes use of the following ALMA data: ADS/JAO.ALMA#2013.1.00111. S. ALMA is a partnership of ESO (representing its member states), NSF (USA), and NINS (Japan), together with NRC (Canada), NSC and ASIAA (Taiwan), and KASI (Republic of Korea), in cooperation with the Republic of Chile. The Joint ALMA Observatory is operated by ESO, AUI/NRAO, and NAOJ. The National Radio Astronomy Observatory is a facility of the National Science Foundation operated under cooperative agreement by Associated Universities, Inc. R.J.I. acknowledges support from ERC in the form of the Advanced Investigator Programme, 321302, COSMICISM.|
|Group:||Infrared Processing and Analysis Center (IPAC), COSMOS|
|Subject Keywords:||cosmology: observations – galaxies: evolution – galaxies: ISM|
|Usage Policy:||No commercial reproduction, distribution, display or performance rights in this work are provided.|
|Deposited By:||Ruth Sustaita|
|Deposited On:||16 Mar 2016 20:58|
|Last Modified:||08 Jul 2016 01:55|
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