[C II] 158 μm EMISSION AS A STAR FORMATION TRACER

Abstract

The [CII] 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 [CII] surface brightness and luminosity with SFR. We conclude that [CII] 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 (AGN). The uncertainty of the Σ [CII] − 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 [CII] − Σ SFR correlation is valid over almost 5 orders of magnitude in Σ SFR , holding for both normal star-forming galaxies and non-AGN luminous infrared galaxies. Using [CII] 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 populationsynthesis code to connect SFR to [CII] finds that heating efficiencies are 1% − 3% in normal galaxies.

The Origins of [C ii] Emission in Local Star-forming Galaxies

“…as a function of the farinfrared color, f n n (70 μm)/ f n n (160 μm) (left), and the star formation rate surface density (right), which was calculated following the procedure of Herrera-Camus et al (2015). This reveals a rough trend such that regions exhibiting a warmer Part of this trend may be the result of chemical evolution due to the star formation history of a galaxy.…”

“…Due to its prominence in the far-IR spectrum, [C II] emission has been used to explore physical processes that occur in the interstellar medium (ISM) of nearby galaxies. For example, [C II] emission has been used to trace the efficiency of heating photon-dominated regions (PDRs) via the photoelectric effect (e.g., Croxall et al 2012), has been used as a calorimetric tracer of the current star formation rate (Stacey et al 1991;De Looze et al 2014; Magdis et al 2014;Herrera-Camus et al 2015), and has been used to diagnose the thermal pressure and ionization fraction of the neutral ISM (e.g., Wolfire et al 1990Wolfire et al , 1995Madden et al 1997;Beirão et al 2010). Furthermore, at high redshift this line becomes one of the principal ways to trace the ISM and early star formation (Iono et al 2006;Stacey et al 2010;Wagg et al 2010;Carilli & Walter 2013;De Breuck et al 2014;Gullberg et al 2015).…”

SIMULATOR OF GALAXY MILLIMETER/SUBMILLIMETER EMISSION (SÍGAME): THE [C ii]–SFR RELATIONSHIP OF MASSIVEz= 2 MAIN SEQUENCE GALAXIES

“…Recent Herschel studies of local spirals and dwarf galaxies have found that C II [ ] remains a robust tracer of star formation over scales ranging from ∼20 pc to~1 kpc (e.g., De Looze et al 2014;Herrera-Camus et al 2015;Kapala et al 2015, hereafter referred to as D14; H15; and K15, respectively). Pineda et al (2014) found that our Galaxy matches these resolved extragalactic C SFR…”

The spatially resolved correlation between [NII] 205μm line emission and the 24μm continuum in nearby galaxies

“…Simply combining all the data to define an average relation is prevented by the aforementioned offset in the individual galaxy relations. To interpret this offset, we use the Starburst99 stellar population synthesis code (Leitherer et al 1999) to model the Σ SFR -F [NII]205 relation following the approach of Herrera-Camus et al (2015), who consider that gas heating by FUV photons emitted from star-forming regions relate to gas cooling from the [N] line via the photoelectric effect in PAHs and dust grains. In brief, we assume a stellar population with a constant SFR over 100 Myr and solar metallicity 3 and adopt the Geneva evolutionary tracks (zero rotation) and Kroupa initial mass function.…”

“…3, we find the vast majority of regions in NGC 891 and M 51 may have been actively forming stars for t d ≥ 20 Myr with ε between 1 and 3%. As a result of the model degeneracy between t d and ε (see Herrera-Camus et al 2015 for details), M 83 and NGC 4038/9 exhibit a stellar population with either a star formation duration of t d ≥ 20 Myr and ε 1% or more recent star formation episodes of t d = 2 Myr and ε between 1 and 3%. This suggests that these two galaxies also possess regions with higher SFRs from recently triggered star formation, likely due to the merger (NGC 4038/9) or central starburst (M 83), as we discuss above.…”