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arXiv · 1808.10331

The [C II] emission as a molecular gas mass tracer in galaxies at low and high redshift

A. Zanella·E. Daddi·G. Magdis·T. Diaz Santos·D. Cormier·D. Liu·A. Cibinel·R. Gobat·M. Dickinson·M. Sargent·G. Popping·S. C. Madden·M. Bethermin·T. M. Hughes·F. Valentino·W. Rujopakarn·M. Pannella·F. Bournaud·F. Walter·T. Wang·D. Elbaz·R. T. Coogan
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Abstract

We present ALMA Band 9 observations of the [C II]158um emission for a sample of 10 main-sequence galaxies at redshift z ~ 2, with typical stellar masses (log M*/Msun ~ 10.0 - 10.9) and star formation rates (~ 35 - 115 Msun/yr). 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]/LIR) of our sample is similar to that of local main-sequence galaxies (~ 2 x 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-H2 conversion factor (alpha_[C II] ~ 30 Msun/Lsun) 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.

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A. Zanella, E. Daddi, G. Magdis, T. Diaz Santos, D. Cormier, D. Liu, A. Cibinel, R. Gobat, M. Dickinson, M. Sargent, G. Popping, S. C. Madden, M. Bethermin, T. M. Hughes, F. Valentino, W. Rujopakarn, M. Pannella, F. Bournaud, F. Walter, T. Wang, D. Elbaz, R. T. Coogan. 2018-08-30. The [C II] emission as a molecular gas mass tracer in galaxies at low and high redshift. https://doi.org/10.1093/mnras/sty2394

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