[C I](1-0) and [C I](2-1) in Resolved Local Galaxies

December 2019 • 2019ApJ...887..105C

Authors • Crocker, Alison F. • Pellegrini, Eric • Smith, J. -D. T. • Draine, Bruce T. • Wilson, Christine D. • Wolfire, Mark • Armus, Lee • Brinks, Elias • Dale, Daniel A. • Groves, Brent • Herrera-Camus, Rodrigo • Hunt, Leslie K. • Kennicutt, Robert C. • Murphy, Eric J. • Sandstrom, Karin • Schinnerer, Eva • Rigopoulou, Dimitra • Rosolowsky, Erik • van der Werf, Paul

Abstract • We present resolved [C I] line intensities of 18 nearby galaxies observed with the SPIRE FTS spectrometer on the Herschel Space Observatory. We use these data along with resolved CO line intensities from J up = 1 to 7 to interpret what phase of the interstellar medium the [C I] lines trace within typical local galaxies. A tight, linear relation is found between the intensities of the CO(4-3) and [C I](2-1) lines; we hypothesize this is due to the similar upper level temperature of these two lines. We modeled the [C I] and CO line emission using large-velocity gradient models combined with an empirical template. According to this modeling, the [C I](1-0) line is clearly dominated by the low-excitation component. We determine [C I] to molecular mass conversion factors for both the [C I](1-0) and [C I](2-1) lines, with mean values of α [C I](1-0) = 7.3 M K-1 km-1 s pc-2 and α [C I](2-1) = 34 M K-1 km-1 s pc-2 with logarithmic root-mean-square spreads of 0.20 and 0.32 dex, respectively. The similar spread of {α }[{{C}{{I}}](1{--}0)} to {α }CO} (derived using the CO(2-1) line) suggests that [C I](1-0) may be just as good a tracer of cold molecular gas as CO(2-1) in galaxies of this type. On the other hand, the wider spread of α [C I](2-1) and the tight relation found between [C I](2-1) and CO(4-3) suggest that much of the [C I](2-1) emission may originate in warmer molecular gas.

Herschel is an ESA space observatory with science instruments provided by European-led Principal Investigator consortia and with important participation from NASA.


IPAC Authors


Lee Armus

Senior Scientist