Star Formation Rates from [C II] 158 μm and Mid-infrared Emission Lines for Starbursts and Active Galactic Nuclei

Sargsyan, L.; Samsonyan, A.; Lebouteiller, V.; Weedman, D.; Barry, D.; Bernard-Salas, J.; Houck, J. and Spoon, H. (2014). Star Formation Rates from [C II] 158 μm and Mid-infrared Emission Lines for Starbursts and Active Galactic Nuclei. The Astrophysical Journal, 790(1), article no. 15.

DOI: https://doi.org/10.1088/0004-637X/790/1/15

Abstract

A summary is presented for 130 galaxies observed with the Herschel Photodetector Array Camera and Spectrometer instrument to measure fluxes for the [C II] 158 μm emission line. Sources cover a wide range of active galactic nucleus to starburst classifications, as derived from polycyclic aromatic hydrocarbon strength measured with the Spitzer Infrared Spectrograph. Redshifts from [C II] and line to continuum strengths (equivalent width (EW) of [C II]) are given for the full sample, which includes 18 new [C II] flux measures. Calibration of L([C II)]) as a star formation rate (SFR) indicator is determined by comparing [C II] luminosities with mid-infrared [Ne II] and [Ne III] emission line luminosities; this gives the same result as determining SFR using bolometric luminosities of reradiating dust from starbursts: log SFR = log L([C II)]) - 7.0, for SFR in M _⊙ yr^-1 and L([C II]) in L _⊙. We conclude that L([C II]) can be used to measure SFR in any source to a precision of ~50%, even if total source luminosities are dominated by an active galactic nucleus (AGN) component. The line to continuum ratio at 158 μm, EW([C II]), is not significantly greater for starbursts (median EW([C II]) = 1.0 μm) compared to composites and AGNs (median EW([C II]) = 0.7 μm), showing that the far-infrared continuum at 158 μm scales with [C II] regardless of classification. This indicates that the continuum at 158 μm also arises primarily from the starburst component within any source, giving log SFR = log νL _ν(158 μm) - 42.8 for SFR in M _⊙ yr-1 and νL _ν(158 μm) in erg s^-1.