Physical Conditions of the Gas in an ALMA [CII]-identified Submillimetre Galaxy at z = 4.44

Huynh, M. T., Norris, R. P., Coppin, Kristen, Emonts, B. H. C., Ivison, R. J., Seymour, N., Smail, Ian, Smolcic, V., Swinbank, A. M., Brandt, W. N., Chapman, S.C., Dannerbauer, H., De Breuck, C., Greve, T. R., Hodge, J. A., Karim, A., Knudsen, K. K., Menten, K.M., van der Werf, P., Walter, F. and Weiss, A. (2013) Physical Conditions of the Gas in an ALMA [CII]-identified Submillimetre Galaxy at z = 4.44. Monthly Notices of the Royal Astronomical Society (MNRAS), 431. L88-L92. ISSN 0035-8711

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We present CO(2-1) observations of the submillimetre galaxy ALESS65.1 performed with the Australia Telescope Compact Array at 42.3 GHz. A previous ALMA study of submillimetre galaxies in the Extended Chandra Deep Field South detected [CII] 157.74 micron emission from this galaxy at a redshift of z = 4.44. No CO(2-1) emission was detected but we derive a firm upper limit to the cold gas mass in ALESS65.1 of M_gas 4 SMGs being the likely progenitors of massive red-and-dead galaxies at z > 2. The ratio of the [CII], CO and far-infrared luminosities implies a strong far-ultraviolet field of G_0 > 10^3, as seen in Galactic star forming regions or local ULIRGs. The observed L_[CII]/L_FIR = 2.3 x 10^{-3} is high compared to local ULIRGs and, combined with L_[CII]/L_CO > 2700, it is consistent with ALESS65.1 either having an extended (several kpc) [CII] emitting region or lower than solar metallicity.