A Survey of Atomic Carbon at High Redshift

TLDR: In this paper, a survey of atomic carbon (C I) emission in high-redshift (z > 2) submillimeter galaxies and quasar host galaxies is presented.

Abstract: 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 P 1 → 3 P 0 ) and C I ( 3 P 2 → 3 P 1 ) 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 CI ( 3 P 2 → 3 P 1 )/CI ( 3 P 1 → Po) and the CI ( 3 P 1 → 3 P 0 )/ 12 CO(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 CI /L FIR ∼ (7.7 ± 4.6) x 10 ―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[CI]/X[H 2 ] ∼ (8.4±3.5)×10 ―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).