WALTER F., WEISS A., DOWNES D., DECARLI R. and HENKEL C.
Abstract (from CDS):
We present a survey of atomic carbon (C I) emission in high-redshift (z > 2) submillimeter galaxies and quasar host galaxies. Sensitive observations of the C I (3 P1 -> 3 P0) and C I (3 P2 -> 3 P1) lines have been obtained at the IRAM Plateau de Bure interferometer and the IRAM 30 m telescope. A total of 16 C I lines have been targeted in 10 sources, leading to a total of 10 detected lines–this doubles the number of C I observations at high redshift to date. We include previously published C I observations (an additional five detected sources) in our analysis. Our main finding is that the C I properties of the high-redshift galaxies studied here do not differ significantly from what is found in low-redshift systems, including the Milky Way. The C I (3 P2 -> 3 P1)/C I (3 P1 -> 3 P0) and the C I (3 P1 -> 3 P0)/12CO(3-2) line luminosity (L') ratios change little in our sample, with respective ratios of 0.55±0.15 and 0.32±0.13. The C I lines are not an important contributor to cooling of the molecular gas (average L_ C I/LFIR_∼ (7.7 ±4.6)x10–6). We derive a mean carbon excitation temperature of 29.1 ±6.3 K, broadly consistent with dust temperatures derived for high-redshift star-forming systems, but lower than gas temperatures typically derived for starbursts in the local universe. The carbon abundance of X[C I]/X[H2] ∼ (8.4±3.5)x10–5 is of the same order as found in the Milky Way and nearby galaxies. This implies that the high-z galaxies studied here are significantly enriched in carbon on galactic scales, even though the look-back times are considerable (the average redshift of the sample sources corresponds to an age of the universe of ∼2 Gyr).