The dusty, albeit ultraviolet bright infancy of galaxies

TL;DR

This study uses hydrodynamical simulations to show that massive early galaxies efficiently form stars and emit UV light that escapes dust, matching observed high-redshift galaxy luminosity functions from redshift 4 to 7.

Contribution

The paper presents a self-consistent dust extinction model in galaxy formation simulations that accurately reproduces observed UV luminosity functions of high-redshift galaxies.

Findings

Simulated UV luminosity functions match observations from redshift 4 to 7.

A significant fraction of UV photons escape dust in primordial galaxies.

Predicted UV-bright galaxies will be detectable by future sub-millimetre telescopes like ALMA.

Abstract

The largest galaxies acquire their mass early on, when the Universe is still youthful. Cold streams violently feed these young galaxies a vast amount of fresh gas, resulting in very efficient star formation. Using a well resolved hydrodynamical simulation of galaxy formation, we demonstrate that these mammoth galaxies are already in place a couple of billion years after the Big Bang. Contrary to local starforming galaxies, where dust re-emits a large part of the stellar ultraviolet (UV) light at infrared and sub-millimetre wavelengths, our self-consistent modelling of dust extinction predicts that a substantial fraction of UV photons should escape from primordial galaxies. Such a model allows us to compute reliably the number of high redshift objects as a function of luminosity, and yields galaxies whose UV luminosities closely match those measured in the deepest observational surveys available. This agreement is remarkably good considering our admittedly still simple modelling of the interstellar medium (ISM) physics. The luminosity functions (LF) of virtual UV luminous galaxies coincide with the existing data over the whole redshift range from 4 to 7, provided cosmological parameters are set to their currently favoured values. Despite their considerable emission at short wavelengths, we anticipate that the counterparts of the brightest UV galaxies will be detected by future sub-millimetre facilities like ALMA