Interferometric CO Observations of submillimeter-faint, radio-selected starburst galaxies at z~2
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Date
2008-12-20Author
Chapman, S. C.
Neri, R.
Bertoldi, F.
Smail, Ian
Greve, T. R.
Trethewey, D.
Blain, A. W.
Cox, P.
Genzel, R.
Ivison, R. J.
Kovacs, A.
Swinbank, A. Omont A. M.
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Show full item recordAbstract
High-redshift, dust-obscured galaxies -- selected to be luminous in the radio but relatively faint at 850um -- appear to represent a different population from the ultra-luminous submillimeter- (submm-) bright population. They may be star-forming galaxies with hotter dust temperatures or they may have lower far-infrared luminosities and larger contributions from obscured active galactic nuclei (AGN). Here we present observations of three z~2 examples of this population, which we term submm-faint radio galaxies (SFRGs) in CO(3-2) using the IRAM Plateau de Bure Interferometer to study their gas and dynamical properties. We estimate the molecular gas mass in each of the three SFRGs (8.3x10^{9} M_odot, =970 M_odot\yr) suggest much higher star-formation efficiencies than are found for SMGs, and shorter gas depletion time scales (~11 Myr), much shorter than the time required to form their current stellar masses (~160 Myr; ~10^{11} M_odot). By contrast, SFRs may be overestimated by factors of a few, bringing the efficiencies in line with those typically measured for other ultraluminous star-forming galaxies and suggesting SFRGs are more like ultraviolet- (UV-)selected star-forming galaxies with enhanced radio emission. A tentative detection of \rga at 350um suggests hotter dust temperatures -- and thus similar gas-to-dust mass fractions -- as the SMGs. We conclude that SFRGs' radio luminosities are larger than would naturally scale from local ULIRGs given their gas masses or gas fractions.
Citation
Chapman, S. C., R. Neri, F. Bertoldi, Ian Smail, et al. 2008. "Interferometric CO Observations of submillimeter-faint, radio-selected starburst galaxies at z~2." The Astrophysical Journal 689(2): 889-896