The formation of supermassive black holes from Population III.1 seeds. III. Galaxy evolution and black hole growth from semi-analytic modelling

Journal article, 2025

We present an implementation of Pop III.1 seeding of supermassive black holes (SMBHs) in a theoretical model of galaxy formation and evolution to assess the growth of the SMBH population and the properties of the host galaxies. The model of Pop III.1 seeding involves SMBH formation at redshifts z greater than or similar to 20 in dark matter minihaloes that are isolated from external radiative feedback, parametrized by isolation distance d(iso). Within a standard Lambda CDM cosmology, we generate dark matter haloes using the code pinocchio and seed them according to the Pop III.1 scenario, exploring values of d(iso) from 50 to 100 kpc (proper distance). We consider two alternative cases of SMBH seeding: a halo mass threshold model in which all haloes > 7 x 10(10 )M(circle dot) are seeded with similar to 10(5 )M(circle dot) black holes; an all light seed model in which all haloes are seeded with low, stellar mass black holes. We follow the redshift evolution of the haloes, populating them with galaxies using the GAlaxy Evolution and Assembly theoretical model of galaxy formation, including accretion on SMBHs and related feedback processes. Here we present predictions for the properties of galaxy populations, focusing on stellar masses, star formation rates, and black hole masses. The local, z similar to 0 metrics of occupation fraction as a function of the galaxy stellar mass, galaxy stellar mass function, and black hole mass function all suggest a constraint of d(iso) < 75 kpc. We discuss the implications of this result for the Pop III.1 seeding mechanism.