Astrophys. J., 890, 24-24 (2020/February-2)
The properties of the interstellar medium of galaxies across time as traced by the neutral atomic carbon [C I].
VALENTINO F., MAGDIS G.E., DADDI E., LIU D., ARAVENA M., BOURNAUD F., CORTZEN I., GAO Y., JIN S., JUNEAU S., KARTALTEPE J.S., KOKOREV V., LEE M.-Y., MADDEN S.C., NARAYANAN D., POPPING G. and PUGLISI A.
Abstract (from CDS):
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∼1, including novel information on [C I](3P2–3P1) and CO (7–6) 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[CI]3P2–3P1^′/L[CI]3P1-3P0_^′^ 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.
© 2020. The American Astronomical Society. All rights reserved.
Galaxy evolution - High-redshift galaxies - Starburst galaxies - Ultraluminous infrared galaxies - Submillimeter astronomy - Interstellar medium - Star formation
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