Physical conditions of the gas in an ALMA C II -identified submillimetre galaxy at z=4.44

Journal article, 2013

We present (CO)-C-12(2-1) observations of the submillimetre galaxy ALESS65.1 performed with the Australia Telescope Compact Array (ATCA) at 42.3 GHz. A previous Atacama Large Millimeter Array study of submillimetre galaxies (SMGs) in the Extended Chandra Deep Field South detected [C II] 157.74 mu m emission from this galaxy at a redshift of z= 4.44. No (CO)-C-12(21) emission was detected but we derive a firm upper limit to the cold gas mass in ALESS65.1 of M-gas < 1.7 x 10(10)M(circle dot). The estimated gas depletion time-scale is < 50 Myr, which is similar to other high-redshift SMGs, and consistent with z > 4 SMGs being the likely progenitors of massive red-and-dead galaxies at z > 2. The ratio of the [CII], (CO)-C-12 and far-infrared luminosities implies a strong far-ultraviolet field of G(0) greater than or similar to 103, as seen in Galactic star-forming regions or local ultraluminous infrared galaxies (ULIRGs). The observed L-[C II]/L-FIR = 2.3 x 10(-3) is high compared to local ULIRGs and, combined withLL([CII])/L-CO greater than or similar to 2700, it is consistent with ALESS65.1 either having an extended (several kpc) [C II] emitting region or lower than solar metallicity.