[C I](1-0) and [C I](2-1) in Resolved Local Galaxies
Hunt, Leslie K.; Wilson, Christine D.; Rosolowsky, Erik; Schinnerer, Eva; Kennicutt, Robert C.; van der Werf, Paul; Brinks, Elias; Dale, Daniel A.; Groves, Brent; Herrera-Camus, Rodrigo; Wolfire, Mark; Smith, J. -D. T.; Sandstrom, Karin; Draine, Bruce T.; Armus, Lee; Murphy, Eric J.; Rigopoulou, Dimitra; Crocker, Alison F.; Pellegrini, Eric
United States, Germany, Canada, United Kingdom, Australia, Chile, Italy, Netherlands
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.