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          Institute: MPI für Astronomie     Collection: Publikationen_mpia     Display Documents

ID: 606568.0, MPI für Astronomie / Publikationen_mpia
GOODS-Herschel: gas-to-dust mass ratios and CO-to-H2 conversion factors in normal and starbursting galaxies at high-z
Authors:Magdis, G. E.; Daddi, E.; Elbaz, D.; Sargent, M.; Dickinson, M.; Dannerbauer, H.; Aussel, H.; Walter, F.; Hwang, H. S.; Charmandaris, V.; Hodge, J.; Riechers, D.; Rigopoulou, D.; Carilli, C.; Pannella, M.; Mullaney, J.; Leiton, R.; Scott, D.
Date of Publication (YYYY-MM-DD):2011
Journal Abbrev.:The Astrophysical Journal Letters
Issue / Number:1
Audience:Not Specified
Abstract / Description:We explore the gas-to-dust mass ratio (M gas/M d) and the CO luminosity-to-M gas conversion factor (αCO) of two well-studied galaxies in the Great Observatories Origins Deep Survey North 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 millimeter (mm) interferometry (1.1-6.6 mm) along with Herschel PACS and SPIRE data that probe the peak of their infrared emission. Using the physically motivated Draine & Li models, as well as a modified blackbody function, we measure the dust mass (M dust) of the sources and find (2.0+0.7 -0.6 × 109) M sun for GN20 and (8.6+0.6 -0.9 × 108) M sun for BzK-21000. The addition of mm data reduces the uncertainties of the derived M dust by a factor of ~2, allowing the use of the local M gas/M d versus metallicity relation to place constraints on the αCO values of the two sources. For GN20 we derive a conversion factor of αCO < 1.0 M sun pc-2 (K km s-1)-1, consistent with that of local ultra-luminous infrared galaxies, while for BzK-21000 we find a considerably higher value, αCO ~4.0 M sun pc-2 (K km s-1)-1, in agreement with an independent kinematic derivation reported previously. The implied star formation efficiency is ~25 L sun/M sun 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.
Free Keywords:galaxies: evolution; galaxies: high-redshift; galaxies: starburst; galaxies: star formation; infrared: galaxies
External Publication Status:published
Document Type:Article
Communicated by:N. N.
Affiliations:MPI für Astronomie
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