The Properties of the Interstellar Medium of Galaxies across Time as Traced by the Neutral Atomic Carbon [C I]
Abstract
We report Atacama Large Millimeter Array observations of the neutral atomic carbon transitions [C I] and multiple CO lines in a sample of ∼30 main-sequence galaxies at $z\sim 1$ , including novel information on [C I] ${(}^{3}{P}_{2}{\mbox{--}}^{3}{P}_{1})$ and CO $(7\mbox{--}6)$ for 7 of such normal objects. We complement our observations with a collection of >200 galaxies with coverage of similar transitions, spanning the z = 0-4 redshift interval and a variety of ambient conditions from local to high-redshift starbursts. We find systematic variations in the [C I]/IR and [C I]/high-Jupper (Jupper = 7) CO luminosity ratios among the various samples. We interpret these differences as increased dense molecular gas fractions and star formation efficiencies in the strongest high-redshift starbursts with respect to normal main-sequence galaxies. We further report constant ${L}_{{[{\rm{C}}{\rm{I}}]}^{3}{P}_{2}\,-{}^{3}{P}_{1}}^{{\prime} }$ / ${L}_{{[{\rm{C}}{\rm{I}}]}^{3}{P}_{1}\,-{}^{3}{P}_{0}}^{{\prime} }$ ratios across the galaxy populations and redshifts, suggesting that gas temperatures Texc traced by [C I] do not strongly vary. We find only a mild correlation with Tdust and that, generally, Texc ≲ Tdust. We fit the line ratios with classical photodissociation region models, retrieving consistently larger densities and intensities of the UV radiation fields in submillimeter galaxies than in main-sequence and local objects. However, these simple models fall short in representing the complexity of a multiphase interstellar medium and should be treated with caution. Finally, we compare our observations with the Santa Cruz semi-analytical model of galaxy evolution, recently extended to simulate submillimeter emission. While we confirm the success in reproducing the CO lines, we find systematically larger [C I] luminosities at fixed IR luminosity than predicted theoretically. This highlights the necessity of improving our understanding of the mechanisms regulating the [C I] emission on galactic scales. We release our data compilation to the community.
- Publication:
-
The Astrophysical Journal
- Pub Date:
- February 2020
- DOI:
- arXiv:
- arXiv:2001.01734
- Bibcode:
- 2020ApJ...890...24V
- Keywords:
-
- Galaxy evolution;
- High-redshift galaxies;
- Starburst galaxies;
- Ultraluminous infrared galaxies;
- Submillimeter astronomy;
- Interstellar medium;
- Star formation;
- 594;
- 734;
- 1570;
- 1735;
- 1647;
- 847;
- 1569;
- Astrophysics - Astrophysics of Galaxies
- E-Print:
- 20 pages + Appendix, accepted for publication in the Astrophysical Journal on Dec. 20th, 2019. The data compilation is available in the online version of the article