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An evolving photoelectric efficiency at cosmic noon?

Published online by Cambridge University Press:  04 June 2020

Jed McKinney Open the ORCID record for Jed McKinney [Opens in a new window] ,
Alexandra Pope ,
Lee Armus ,
Ranga Chary ,
Mark Dickinson  and
Allison Kirkpatrick
Jed McKinney
Affiliation:
Department of Astronomy, University of Massachusetts, Amherst, MA01003, USA
Alexandra Pope
Affiliation:
Department of Astronomy, University of Massachusetts, Amherst, MA01003, USA
Lee Armus
Affiliation:
Infrared Processing and Analysis Center, MC 314-6, Caltech, 1200 E. California Blvd., Pasadena, CA91125, USA
Ranga Chary
Affiliation:
Division of Physics, Math & Astronomy, California Institute of Technology, Pasadena, CA91125
Mark Dickinson
Affiliation:
National Optical Astronomy Observatory, 950 North Cherry Avenue, Tucson, AZ85719, USA
Allison Kirkpatrick
Affiliation:
Department of Physics & Astronomy, University of Kansas, Lawrence, KS66045, USA
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Abstract

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To sustain star formation rates (SFRs) of hundreds to thousands of solar masses per year over millions of years, a galaxy must efficiently cool its gas. At z ∼ 2, the peak epoch for stellar mass assembly, tracers of gas heating and cooling remain largely unexplored. For one z ∼ 2 starburst galaxy GS IRS20, we present Spitzer IRS spectroscopy of Polycyclic Aromatic Hydrocarbon (PAH) emission, and ALMA observations of [C II] 158 μm fine-structure emission which we use to probe ISM heating/cooling. Coupled with an unusually warm dust component, the ratio of [C II] /PAH emission suggests a low photolelectric efficiency, and/or the importance of cooling from other far-IR lines in this galaxy. A low photoelectric efficiency at z ∼ 2 could be key for the peak in the SFR density of the universe by decoupling stellar radiation from ISM gas temperatures.

Keywords

galaxies: high-redshiftgalaxies: individualgalaxies: ISMgalaxies: starburst

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