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

Abstract

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 < 1.7 x 10^10 M_odot. The estimated gas depletion timescale 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 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.

6 pages, 2 figures, accepted by MNRAS

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• CO(1-0) survey of high-z radio galaxies: alignment of molecular halo gas with distant radio sources
• Physical properties of z>4 submillimeter galaxies in the COSMOS field
• The ALMA Patchy Deep Survey: A blind search for [CII] emitters at z~4.5
• Detection of molecular gas in an ALMA [CII]-identified Submillimetre Galaxy at z = 4.44
• Neon and [CII] 158 micron Emission Line Profiles in Dusty Starbursts and Active Galactic Nuclei
• Dusty Quasars at High Redshifts