A dust-obscured massive maximum-starburst galaxy at a redshift of 6.34

Riechers, Dominik A. and Bradford, C. M. and Clements, D. L. and Dowell, C. D. and Pérez-Fournon, I. and Ivison, R. J. and Bridge, C. and Conley, A. and Fu, Hai and Vieira, J. D. and Wardlow, J. and Calanog, J. and Cooray, A. and Hurley, P. and Neri, R. and Kamenetzky, J. and Aguirre, J. E. and Altieri, B. and Arumugam, V. and Benford, D. J. and Béthermin, M. and Bock, J. and Burgarella, D. and Cabrera-Lavers, A. and Chapman, S. C. and Cox, P. and Dunlop, J. S. and Earle, L. and Farrah, D. and Ferrero, P. and Franceschini, A. and Gavazzi, R. and Glenn, J. and Solares, E. A. Gonzalez and Gurwell, M. A. and Halpern, M. and Hatziminaoglou, E. and Hyde, A. and Ibar, E. and Kovács, A. and Krips, M. and Lupu, R. E. and Maloney, P. R. and Martinez-Navajas, P. and Matsuhara, H. and Murphy, E. J. and Naylor, B. J. and Nguyen, H. T. and Oliver, S. J. and Omont, A. and Page, M. J. and Petitpas, G. and Rangwala, N. and Roseboom, I. G. and Scott, D. and Smith, A. J. and Staguhn, J. G. and Streblyanska, A. and Thomson, A. P. and Valtchanov, I. and Viero, M. and Wang, L. and Zemcov, M. and Zmuidzinas, J. (2013) A dust-obscured massive maximum-starburst galaxy at a redshift of 6.34. Nature, 496 (7445). pp. 329-333. ISSN 0028-0836

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Abstract

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.