A candidate redshift z~10 galaxy and rapid changes in that population at an age of 500Myr
Trenti, M.; Oesch, P. A.; Carollo, C. M.; Stiavelli, M.; Bouwens, R. J.; Illingworth, G. D.; Franx, M.; van Dokkum, P. G.; Labbe, I.; Bradley, L.; Magee, D.; González, V.
United States, Switzerland, Netherlands
Abstract
Searches for very-high-redshift galaxies over the past decade have yielded a large sample of more than 6,000 galaxies existing just 900-2,000million 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 500Myr 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 ~200Myr 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 100-200Myr before z~10 is clearly a crucial phase in the assembly of the earliest galaxies.