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Published February 10, 2015 | Published + Submitted
Journal Article Open

[C II] 158 μm Emission as a Star Formation Tracer

Abstract

The [C II] 157.74 μm transition is the dominant coolant of the neutral interstellar gas, and has great potential as a star formation rate (SFR) tracer. Using the Herschel KINGFISH sample of 46 nearby galaxies, we investigate the relation of [C II] surface brightness and luminosity with SFR. We conclude that [C II] can be used for measurements of SFR on both global and kiloparsec scales in normal star-forming galaxies in the absence of strong active galactic nuclei (AGNs). The uncertainty of the Σ_([C II]) – Σ_(SFR) calibration is ±0.21 dex. The main source of scatter in the correlation is associated with regions that exhibit warm IR colors, and we provide an adjustment based on IR color that reduces the scatter. We show that the color-adjusted Σ_([C II]) – Σ_(SFR) correlation is valid over almost five orders of magnitude in Σ_(SFR), holding for both normal star-forming galaxies and non-AGN luminous infrared galaxies. Using [C II] luminosity instead of surface brightness to estimate SFR suffers from worse systematics, frequently underpredicting SFR in luminous infrared galaxies even after IR color adjustment (although this depends on the SFR measure employed). We suspect that surface brightness relations are better behaved than the luminosity relations because the former are more closely related to the local far-UV field strength, most likely the main parameter controlling the efficiency of the conversion of far-UV radiation into gas heating. A simple model based on Starburst99 population-synthesis code to connect SFR to [C II] finds that heating efficiencies are 1%-3% in normal galaxies.

Additional Information

© 2015 American Astronomical Society. Received 2014 July 3; accepted 2014 September 20; published 2015 February 2. We thank the referee for constructive and valuable comments on the paper. R.H.C. acknowledges support from a Fulbright-CONICYT grant. A.D.B. acknowledges partial support from a CAREER grant NSF-AST0955836, from NSF-AST1139998, from NASA-JPL 1373858, and from a Research Corporation for Science Advancement Cottrell Scholar award. We thank B. Weiner for providing [C ii] and FIR fluxes for his sample of LIRGs in advance of publication. We also thank T. Diaz-Santos for providing the areas used to measure the surface brightness of the galaxies in the GOALS sample in advance of publication. PACS has been developed by a consortium of institutes led by MPE (Germany) and including UVIE (Austria); KU Leuven, CSL, IMEC (Belgium); CEA, LAM (France);MPIA (Germany); INAF-IFSI/OAA/OAP/OAT, LENS, SISSA (Italy); IAC (Spain). This development has been supported by the funding agencies BMVIT (Austria), ESA-PRODEX (Belgium), CEA/CNES (France), DLR (Germany), ASI/INAF (Italy), and CICYT/MCYT (Spain). HIPE is a joint development by the Herschel Science Ground Segment Consortium, consisting of ESA, the NASA Herschel Science Center, and the HIFI, PACS, and SPIRE consortia. This work is based (in part) on observations made with Herschel, a European Space Agency Cornerstone Mission with significant participation by NASA. The National Radio Astronomy Observatory is a facility of the National Science Foundation operated under cooperative agreement by Associated Universities, Inc. This research has made use of the NASA/IPAC Extragalactic Database (NED), which is operated by the Jet Propulsion Laboratory, California Institute of Technology, under contract with the National Aeronautics and Space Administration. We wish to dedicate this study to the memory of our colleague Dr. Charles "Chad" Engelbracht for his numerous contributions to space-based far-infrared astronomy that made this work possible, as well as that of many other researchers employing Spitzer and Herschel observations.

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Published - 0004-637X_800_1_1.pdf

Submitted - 1409.7123v1.pdf

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