[CII] 158 micron Luminosities and Star Formation Rate in Dusty Starbursts and AGN

TL;DR

This study investigates the relationship between [CII] 158 micron line flux and star formation rates in dusty starbursts and AGN, establishing a calibration method and analyzing the [CII] deficit in luminous sources.

Contribution

It provides a new calibration for star formation rate based on [CII] luminosity and demonstrates the link between [CII] emission and starburst activity independent of AGN influence.

Findings

[CII] flux correlates with 11.3 micron PAH flux regardless of AGN/starburst classification.

A calibration formula for star formation rate using [CII] luminosity is derived.

The [CII] deficit in luminous sources is explained by the dominance of AGN in IR emission.

Abstract

Results are presented for [CII] 158 micron line fluxes observed with the Herschel PACS instrument in 112 sources with both starburst and AGN classifications, of which 102 sources have confident detections. Results are compared with mid-infrared spectra from the Spitzer Infrared Spectrometer and with L(IR) from IRAS fluxes; AGN/starburst classifications are determined from equivalent width of the 6.2 micron PAH feature. It is found that the [CII] line flux correlates closely with the flux of the 11.3 micron PAH feature independent of AGN/starburst classification, log [f([CII] 158 micron)/f(11.3 micron PAH)] = -0.22 +- 0.25. It is concluded that [CII] line flux measures the photodissociation region associated with starbursts in the same fashion as the PAH feature. A calibration of star formation rate for the starburst component in any source having [CII] is derived comparing [CII] luminosity L([CII]) to L(IR) with the result that log SFR = log L([CII)]) - 7.08 +- 0.3, for SFR in solar masses per year and L([CII]) in solar luminosities. The decreasing ratio of L([CII]) to L(IR) in more luminous sources (the "[CII] deficit") is shown to be a consequence of the dominant contribution to L(IR) arising from a luminous AGN component because the sources with largest L(IR) and smallest L([CII])/L(IR) are AGN.