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Published September 2010 | Published
Journal Article Open

Detection of molecular gas in a distant submillimetre galaxy at z= 4.76 with Australia Telescope Compact Array


We have detected the CO(2–1) transition from the submillimetre galaxy (SMG) LESS J033229.4−275619 at z= 4.755 using the new Compact Array Broadband Backend system on the Australian Telescope Compact Array. These data have identified a massive gas reservoir available for star formation for the first time in an SMG at z~ 5. We use the luminosity and velocity width (full width at half-maximum, FWHM, of ≃160 km s^(−1)) of the CO(2–1) line emission to constrain the gas and dynamical mass of M_(gas)≃ 1.6 × 10^(10) M_⊙ and Mdyn(<2 kpc) ≃ 5 × 10^(10) (0.25/sin^(2)i) M_⊙, respectively, similar to that observed for SMGs at lower redshifts of z~ 2–4, although we note that our observed CO FWHM is a factor of ~3 narrower than typically seen in SMGs. Together with the stellar mass we estimate a total baryonic mass of M_(bary)≃ 1 × 10^(11) M_⊙, consistent with the dynamical mass for this young galaxy within the uncertainties. Dynamical and baryonic mass limits of high-redshift galaxies are useful tests of galaxy formation models: using the known z~ 4–5 SMGs as examples of massive baryonic systems, we find that their space density is consistent with that predicted by current galaxy formation models. In addition, these observations have helped to confirm that z~ 4–5 SMGs possess the baryonic masses and gas consumption time-scales necessary to be the progenitors of the luminous old red galaxies seen at z~ 3. Our results provide a preview of the science that ALMA will enable on the formation and evolution of the earliest massive galaxies in the Universe.

Additional Information

© 2010 The Authors. Journal compilation © 2010 Royal Astronomical Society. Accepted 2010 July 5. Received 2010 June 17; in original form 2010 April 22. Article first published online: 12 Aug. 2010. We thank an anonymous referee for suggestions which improved the Letter. KEKC acknowledges support from a Science and Technology Facilities Council (STFC) fellowship. We thank John Helly, Carlton Baugh and Cedric Lacey for help with extracting information from the Millenium and GALFORM data bases. IS and JLW acknowledge support from STFC, and AMS acknowledges support from a Lockyer fellowship. JSD acknowledges the support of the Royal Society via a Wolfson Research merit Award. TRG acknowledges support from IDA. The DARK Cosmology Centre is funded by DNRF. The ATCA is part of the Australia Telescope which is funded by the Commonwealth of Australia for operation as a National Facility managed by CSIRO. We thank Stefano Zibetti and Nelson Padilla for the HAWK-I imaging which was obtained during ESO programme ID 082.A-0890.

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August 22, 2023
August 22, 2023