Evaluating the Stellar to Halo Mass Relation in Galaxies Generated by the SHARK Semi-Analytic Model

Abstract

In the hierarchical model of structure formation, galaxies form and evolve within dark matter halos that grow through accretion and mergers. The stellar to halo mass relation (SHMR) characterizes the efficiency of galaxy formation by quantifying how baryonic structures (stellar mass) build up within these halos. This relation is a key constraint on galaxy formation models, reflecting the balance between star formation and feedback processes that quench star formation. This research evaluates how the SHMR varies across different galaxy environments within the SHARK semi-analytic model (SAM). SAMs work by applying physics-based models to precomputed dark matter halo merger trees. This approach is less computationally expensive when compared to hydrodynamic simulations, allowing us to test different physics models quickly and generate enormous samples of galaxies. SHARK is a novel SAM that is uniquely modular and open-source. We explore the SHMR as a function of galaxy properties and properties of their host environments, and from present day to when the Universe was half its current age (from redshift 0 to 1). Our results confirm that central galaxies, the most massive galaxy in a group residing in the centre of the halo, closely follow observed and simulated SHMR trends. In contrast, smaller galaxies orbiting the central (satellites) are quenched, exhibiting systematically lower SHMR, stellar mass, and cold gas mass—up to multiple orders of magnitude. Additionally, the SHMR shows remarkably little evolution over our redshift range, suggesting that the mechanisms that shape the SMHR are well in place when the Universe reached half its age.