A candidate redshift z ~ 10 galaxy and rapid changes in that population at an age of 500 Myr

TL;DR

This study uses deep Hubble data to identify potential galaxies at redshift ~10, revealing rapid galaxy formation and significant evolution in star formation rate density within 200 million years after the Big Bang.

Contribution

It provides the first ultra-deep search for z ~ 10 galaxies and quantifies the rapid increase in galaxy build-up during this epoch.

Findings

Detection of a possible z ~ 10 galaxy candidate

Star formation rate density at z ~ 10 is about 10% of that at z ~ 8

Rapid increase in galaxy luminosity and volume density from z ~ 10 to z ~ 8

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 gamma-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. 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 ~ 8 to z ~ 10. The 100-200 Myr before z ~ 10 is clearly a crucial phase in the assembly of the earliest galaxies.