We present ALMA Band 9 observations of the [C II]158µ m emission for a sample of 10 main-sequence galaxies at redshift z∼2, with typical stellar masses (log M /M ∼10.0-10.9) and star formation rates (∼35-115 M yr −1 ). Given the strong and well understood evolution of the interstellar medium from the present to z = 2, we investigate the behaviour of the [C II] emission and empirically identify its primary driver. We detect [C II] from six galaxies (four secure, two tentative) and estimate ensemble averages including non detections. The [C II]-to-infrared luminosity ratio (L [C II] /L IR ) of our sample is similar to that of local main-sequence galaxies (∼ 2 × 10 −3 ), and ∼ 10 times higher than that of starbursts. The [C II] emission has an average spatial extent of 4 -7 kpc, consistent with the optical size. Complementing our sample with literature data, we find that the [C II] luminosity correlates with galaxies' molecular gas mass, with a mean absolute deviation of 0.2 dex and without evident systematics: the [C II]-to-H 2 conversion factor (α [C II] ∼ 30 M /L ) is largely independent of galaxies' depletion time, metallicity, and redshift. [C II] seems therefore a convenient tracer to estimate galaxies' molecular gas content regardless of their starburst or main-sequence nature, and extending to metal-poor galaxies at low-and high-redshifts. The dearth of [C II] emission reported for z > 6-7 galaxies might suggest either a high star formation efficiency or a small fraction of UV light from star formation reprocessed by dust.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.