Ancient giants: on the farthest galaxy at z=8.6

TL;DR

This paper investigates the physical properties and detectability of the high-redshift galaxy UDFy-38135539 at z=8.6, using cosmological simulations to understand its nature and the conditions of the early universe.

Contribution

It provides a detailed analysis of the galaxy's properties and predicts the likelihood of detecting similar galaxies with JWST and HST, based on simulations and observations.

Findings

UDFy-38135539 has a star formation rate of ~2.7-3.7 solar masses/yr.

The galaxy contains ~10^{8.3-8.7} solar masses of stars, aged 50-80 Myr.

Detection probability is 70% with JWST within 0.4 Mpc radius.

Abstract

The observational frontiers for the detection of high-redshift galaxies have recently been pushed to unimaginable distances with the record-holding Lyman Alpha Emitter (LAE) UDFy-38135539 discovered at redshift z=8.6. However, the physical nature and the implications of this discovery have yet to be assessed. By selecting galaxies with observed luminosities similar to UDFy-38135539 in state-of-the-art cosmological simulations tuned to reproduce the large scale properties of LAEs, we bracket the physical nature of UDFy-38135539: it has a star formation rate ~ 2.7-3.7 solar masses/yr, it contains ~ 10^{8.3-8.7} solar mass of stars 50-80 Myr old, with stellar metallicity ~ 0.03-0.12 of the solar value. For any of the simulated galaxies to be visible as a LAE in the observed range, the intergalactic neutral hydrogen fraction at z=8.6 must be <= 0.2 and extra ionizing radiation from sources clustered around UDFy-38135539 is necessary. Finally, we predict that there is a 70% (15%) probability of detecting at least 1 such source from JWST (HST/WFC3) observations in a physical radius ~ 0.4 Mpc around UDFy-38135539.