The Minimum Halo Mass for Star Formation at z = 6 - 8

TL;DR

This study uses cosmological simulations and Hubble Frontier Fields data to determine the minimum dark matter halo and stellar masses that host star formation at redshifts 6 to 8, challenging previous assumptions.

Contribution

It provides new constraints on the minimum halo and stellar masses for star formation at high redshift based on recent observations and simulations.

Findings

Star formation occurs in halos as small as ~3-10 billion solar masses at z=6-8.

Observations probe stellar masses down to ~8-32 million solar masses.

Results differ from previous models, highlighting the need for further data.

Abstract

Recent analysis of strongly-lensed sources in the Hubble Frontier Fields indicates that the rest-frame UV luminosity function of galaxies at $z=$6--8 rises as a power law down to $M_\mathrm{UV}=-15$, and possibly as faint as -12.5. We use predictions from a cosmological radiation hydrodynamic simulation to map these luminosities onto physical space, constraining the minimum dark matter halo mass and stellar mass that the Frontier Fields probe. While previously-published theoretical studies have suggested or assumed that early star formation was suppressed in halos less massive than $10^9$--$10^{11} M_\odot$, we find that recent observations demand vigorous star formation in halos at least as massive as (3.1, 5.6, 10.5)$\times10^9 M_\odot$ at $z=(6,7,8)$. Likewise, we find that Frontier Fields observations probe down to stellar masses of (8.1, 18, 32)$\times10^6 M_\odot$; that is, they are observing the likely progenitors of analogues to Local Group dwarfs such as Pegasus and M32. Our simulations yield somewhat different constraints than two complementary models that have been invoked in similar analyses, emphasizing the need for further observational constraints on the galaxy-halo connection.