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arXiv · 1109.1140

GOODS-Herschel~: Gas-to-dust mass ratios and CO-to-H_2 conversion factors in normal and starbursting galaxies at high-z

Georgios E. Magdis·E. Daddi·E. Elbaz·M. Sargent·M. Dickinson·H. Dannerbauer·H. Aussel·F. Walter·H. S. Hwang·V. Charmandaris·J. Hodge·D. Riechers·D. Rigopoulou·C. Carilli·M. Pannella·J. Mullaney·R. Leiton·D. Scott
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Abstract

We explore the gas-to-dust mass ratio (G/D) and the CO luminosity-to-Mgas conversion factor (a_co) of two well studied galaxies in the GOODS-N field, that are expected to have different star forming modes, the starburst GN20 at z=4.05 and the normal star-forming galaxy BzK-21000 at z=1.52. Detailed sampling is available for their Rayleigh-Jeans emission via ground based mm interferometry (1.1-6.6mm) along with Herschel, PACS and SPIRE data that probe the peak of their infrared emission. Using the physically motivated Draine & Li (2007) models, as well as a modified black body function, we measure the dust mass (Md) of the sources and find 2.0^{+0.7}_{-0.6} x 10^{9} Msun for GN20 and 8.6^{+0.6}_{-0.9} x 10^{8} Msun for BzK-21000. The addition of mm data reduces the uncertainties of the derived Md by a factor of ~2, allowing the use of the local G\D vs metallicity relation to place constraints on the a_co values of the two sources. For GN20 we derive a conversion factor of a_co < 1.0 Msun pc^{-2}(K km s^{-1})^{-1}, consistent with that of local ULIRGs, while for BzK-21000 we find a considerably higher value, a_co ~4.0 Msun pc^{-2}(K km s^{-1})^{-1}, in agreement with an independent kinematic derivation reported previously. The implied star formation efficiency is ~25 Lsun/Msun for BzK-21000, a factor of ~5-10 lower than that of GN20. The findings for these two sources support the existence of different disk-like and starburst star-formation modes in distant galaxies, although a larger sample is required to draw statistically robust results

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Georgios E. Magdis, E. Daddi, E. Elbaz, M. Sargent, M. Dickinson, H. Dannerbauer, H. Aussel, F. Walter, H. S. Hwang, V. Charmandaris, J. Hodge, D. Riechers, D. Rigopoulou, C. Carilli, M. Pannella, J. Mullaney, R. Leiton, D. Scott. 2011-09-06. GOODS-Herschel~: Gas-to-dust mass ratios and CO-to-H_2 conversion factors in normal and starbursting galaxies at high-z. https://doi.org/10.1088/2041-8205%2F740%2F1%2Fl15

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