title: A candidate redshift z ≈ 10 galaxy and rapid changes in that population at an age of 500 Myr.
abstract: Searches for very-high-redshift galaxies over the past decade have yielded a large sample of more than 6,000 galaxies existing just 900-2,000 million years (Myr) after the Big Bang (redshifts 6 > z > 3; ref. 1). The Hubble Ultra Deep Field (HUDF09) data have yielded the first reliable detections of z ≈ 8 galaxies that, together with reports of a γ-ray burst at z ≈ 8.2 (refs 10, 11), constitute the earliest objects reliably reported to date. Observations of z ≈ 7-8 galaxies suggest substantial star formation at z > 9-10 (refs 12, 13). Here we use the full two-year HUDF09 data to conduct an ultra-deep search for z ≈ 10 galaxies in the heart of the reionization epoch, only 500 Myr after the Big Bang. Not only do we find one possible z ≈ 10 galaxy candidate, but we show that, regardless of source detections, the star formation rate density is much smaller (∼10%) at this time than it is just ∼200 Myr later at z ≈ 8. This demonstrates how rapid galaxy build-up was at z ≈ 10, as galaxies increased in both luminosity density and volume density from z ≈ 10 to z ≈ 8. The 100-200 Myr before z ≈ 10 is clearly a crucial phase in the assembly of the earliest galaxies.
authors.affiliation: Department of Astronomy, University of California Santa Cruz, Santa Cruz, California 95064, USA. bouwens@ucolick.org
authors.forename: R J
authors.initials: RJ
authors.lastname: Bouwens
authors.forename: G D
authors.initials: GD
authors.lastname: Illingworth
authors.forename: I
authors.initials: I
authors.lastname: Labbe
authors.forename: P A
authors.initials: PA
authors.lastname: Oesch
authors.forename: M
authors.initials: M
authors.lastname: Trenti
authors.forename: C M
authors.initials: CM
authors.lastname: Carollo
authors.forename: P G
authors.initials: PG
authors.lastname: van Dokkum
authors.forename: M
authors.initials: M
authors.lastname: Franx
authors.forename: M
authors.initials: M
authors.lastname: Stiavelli
authors.forename: V
authors.initials: V
authors.lastname: González
authors.forename: D
authors.initials: D
authors.lastname: Magee
authors.forename: L
authors.initials: L
authors.lastname: Bradley