A dust-obscured massive maximum-starburst galaxy at a redshift of 6.34
Massive present-day early-type (elliptical and lenticular) galaxies probably gained the bulk of their stellar mass and heavy elements through intense, dust-enshrouded starbursts—that is, increased rates of star formation—in the most massive dark-matter haloes at early epochs. However, it remains unknown how soon after the Big Bang massive starburst progenitors exist. The measured redshift (z) distribution of dusty, massive starbursts has long been suspected to be biased low in z owing to selection effects, as confirmed by recent findings of systems with redshifts as high as ~5 (refs 2–4). Here we report the identification of a massive starburst galaxy at z = 6.34 through a submillimetre colour-selection technique. We unambiguously determined the redshift from a suite of molecular and atomic fine-structure cooling lines. These measurements reveal a hundred billion solar masses of highly excited, chemically evolved interstellar medium in this galaxy, which constitutes at least 40 per cent of the baryonic mass. A 'maximum starburst' converts the gas into stars at a rate more than 2,000 times that of the Milky Way, a rate among the highest observed at any epoch. Despite the overall downturn in cosmic star formation towards the highest redshifts, it seems that environments mature enough to form the most massive, intense starbursts existed at least as early as 880 million years after the Big Bang.
Additional Information© 2013 Macmillan Publishers Limited. Received 4 October 2012; accepted 27 February 2013. Herschel is an ESA space observatory with science instruments provided by European-led Principal Investigator consortia and with important participation from NASA. This research has made use of data from the HerMES project. HerMES is a Herschel Key Programme using guaranteed time from the SPIRE instrument team, ESAC scientists and a mission scientist. See Supplementary Information for further acknowledgements. Author Contributions: D.A.R. had the overall lead of the project. C.M.B., D.L.C., I.P.-F., R.J.I., C.B., H.F., J.D.V. and R.N. contributed significantly to the taking and analysis of the follow-up data with different instruments by leading several telescope proposals and analysis efforts. C.D.D. led the selection of the parent sample. A. Conley, J.W., J.C., A. Cooray, P.H. and J.K. contributed significantly to the data analysis and to fitting and modelling the results. All other authors contributed to the proposals, source selection, data analysis and interpretation, in particular through work on the primary Herschel SPIRE data in which the source was discovered through the HerMES consortium(led by J.B. and S.J.O.). All authors have reviewed, discussed, and commented on the manuscript.
Accepted Version - 1304.4256.pdf
Supplemental Material - nature12050-s1.pdf