title: A dust-obscured massive maximum-starburst galaxy at a redshift of 6.34.
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.
authors.affiliation: California Institute of Technology, 1200 East California Boulevard, MC 249-17, Pasadena, California 91125, USA. dr@astro.cornell.edu
authors.forename: Dominik A
authors.initials: DA
authors.lastname: Riechers
authors.forename: C M
authors.initials: CM
authors.lastname: Bradford
authors.forename: D L
authors.initials: DL
authors.lastname: Clements
authors.forename: C D
authors.initials: CD
authors.lastname: Dowell
authors.forename: I
authors.initials: I
authors.lastname: Pérez-Fournon
authors.forename: R J
authors.initials: RJ
authors.lastname: Ivison
authors.forename: C
authors.initials: C
authors.lastname: Bridge
authors.forename: A
authors.initials: A
authors.lastname: Conley
authors.forename: Hai
authors.initials: H
authors.lastname: Fu
authors.forename: J D
authors.initials: JD
authors.lastname: Vieira
authors.forename: J
authors.initials: J
authors.lastname: Wardlow
authors.forename: J
authors.initials: J
authors.lastname: Calanog
authors.forename: A
authors.initials: A
authors.lastname: Cooray
authors.forename: P
authors.initials: P
authors.lastname: Hurley
authors.forename: R
authors.initials: R
authors.lastname: Neri
authors.forename: J
authors.initials: J
authors.lastname: Kamenetzky
authors.forename: J E
authors.initials: JE
authors.lastname: Aguirre
authors.forename: B
authors.initials: B
authors.lastname: Altieri
authors.forename: V
authors.initials: V
authors.lastname: Arumugam
authors.forename: D J
authors.initials: DJ
authors.lastname: Benford
authors.forename: M
authors.initials: M
authors.lastname: Béthermin
authors.forename: J
authors.initials: J
authors.lastname: Bock
authors.forename: D
authors.initials: D
authors.lastname: Burgarella
authors.forename: A
authors.initials: A
authors.lastname: Cabrera-Lavers
authors.forename: S C
authors.initials: SC
authors.lastname: Chapman
authors.forename: P
authors.initials: P
authors.lastname: Cox
authors.forename: J S
authors.initials: JS
authors.lastname: Dunlop
authors.forename: L
authors.initials: L
authors.lastname: Earle
authors.forename: D
authors.initials: D
authors.lastname: Farrah
authors.forename: P
authors.initials: P
authors.lastname: Ferrero
authors.forename: A
authors.initials: A
authors.lastname: Franceschini
authors.forename: R
authors.initials: R
authors.lastname: Gavazzi
authors.forename: J
authors.initials: J
authors.lastname: Glenn
authors.forename: E A Gonzalez
authors.initials: EA
authors.lastname: Solares
authors.forename: M A
authors.initials: MA
authors.lastname: Gurwell
authors.forename: M
authors.initials: M
authors.lastname: Halpern
authors.forename: E
authors.initials: E
authors.lastname: Hatziminaoglou
authors.forename: A
authors.initials: A
authors.lastname: Hyde
authors.forename: E
authors.initials: E
authors.lastname: Ibar
authors.forename: A
authors.initials: A
authors.lastname: Kovács
authors.forename: M
authors.initials: M
authors.lastname: Krips
authors.forename: R E
authors.initials: RE
authors.lastname: Lupu
authors.forename: P R
authors.initials: PR
authors.lastname: Maloney
authors.forename: P
authors.initials: P
authors.lastname: Martinez-Navajas
authors.forename: H
authors.initials: H
authors.lastname: Matsuhara
authors.forename: E J
authors.initials: EJ
authors.lastname: Murphy
authors.forename: B J
authors.initials: BJ
authors.lastname: Naylor
authors.forename: H T
authors.initials: HT
authors.lastname: Nguyen
authors.forename: S J
authors.initials: SJ
authors.lastname: Oliver
authors.forename: A
authors.initials: A
authors.lastname: Omont
authors.forename: M J
authors.initials: MJ
authors.lastname: Page
authors.forename: G
authors.initials: G
authors.lastname: Petitpas
authors.forename: N
authors.initials: N
authors.lastname: Rangwala
authors.forename: I G
authors.initials: IG
authors.lastname: Roseboom
authors.forename: D
authors.initials: D
authors.lastname: Scott
authors.forename: A J
authors.initials: AJ
authors.lastname: Smith
authors.forename: J G
authors.initials: JG
authors.lastname: Staguhn
authors.forename: A
authors.initials: A
authors.lastname: Streblyanska
authors.forename: A P
authors.initials: AP
authors.lastname: Thomson
authors.forename: I
authors.initials: I
authors.lastname: Valtchanov
authors.forename: M
authors.initials: M
authors.lastname: Viero
authors.forename: L
authors.initials: L
authors.lastname: Wang
authors.forename: M
authors.initials: M
authors.lastname: Zemcov
authors.forename: J
authors.initials: J
authors.lastname: Zmuidzinas