Exploring the Cosmic Evolution of Habitability with Galaxy Merger Trees

TL;DR

This study investigates how galaxy mergers and energetic astrophysical events influence the potential habitability of galaxies over cosmic time, highlighting the importance of detailed merger histories in habitability assessments.

Contribution

It combines galaxy evolution models with transient event rates to analyze the evolution of habitable stellar mass fractions considering merger histories.

Findings

18% of stellar mass irradiated in last 260 Myr, mainly by GRBs

No strong dependence of habitability on galaxy mass or environment

Galaxies can retain high habitability fractions over billions of years

Abstract

We combine inferred galaxy properties from a semi-analytic galaxy evolution model incorporating dark matter halo merger trees with new estimates of supernova and gamma ray burst rates as a function of metallicity from stellar population synthesis models incorporating binary interactions. We use these to explore the stellar mass fraction of galaxies irradiated by energetic astrophysical transients and its evolution over cosmic time, and thus the fraction which is potentially habitable by life like our own. We find that 18 per cent of the stellar mass in the Universe is likely to have been irradiated within the last 260 Myr, with GRBs dominating that fraction. We do not see a strong dependence of irradiated stellar mass fraction on stellar mass or richness of the galaxy environment. We consider a representative merger tree as a Local Group analogue, and find that there are galaxies at all masses which have retained a high habitable fraction (>40 per cent) over the last 6 Gyr, but also that there are galaxies at all masses where the merger history and associated star formation have rendered galaxies effectively uninhabitable. This illustrates the need to consider detailed merger trees when evaluating the cosmic evolution of habitability.