Published
L-GALAXIES 2020: the formation and chemical evolution of stellar haloes in Milky Way analogues and galaxy clusters

Geoff Murphy, Rob Yates, Shazrene Mohamed

We present an analysis of the formation and chemical evolution of stellar haloes around (a) Milky Way Analogue (MWA) galaxies and (b) galaxy clusters in the L-GALAXIES 2020 semi-analytic model of galaxy evolution. Observed stellar halo properties are better reproduced by a gradual disruption model for tidal stripping of stars from satellites compared to an instantaneous disruption model. The slope of the stellar mass -- metallicity relation for MWA stellar haloes is in good agreement with that observed in the local Universe, when scaling to the observed aperture. This extends the good agreement between L-GALAXIES 2020 and metallicity observations from the gas and stars inside galaxies to those outside. Halo stars contribute on average only ~0.1 per cent of the total circumgalactic medium (CGM) enrichment by z=0 in MWAs, ejecting predominantly carbon produced by AGB stars. Around a quarter of MWAs have a single `significant progenitor' with a mean mass of ~2.3x10^9 Msun, similar to that measured for Gaia Enceladus. For galaxy clusters, L-GALAXIES 2020 shows good correspondence with observations of the total cluster stellar mass and stellar halo mass fractions. Assuming a Navarro-Frenk-White profile for the stellar halo mass distribution provides the best agreement. On average, the intracluster stellar component (ICS) is responsible for 5.4 per cent of the total intracluster medium (ICM) iron enrichment, exceeding the contribution from the brightest cluster galaxy (BCG) by z=0. We find that considering gradual disruption of satellites and realistic radial profiles is crucial for accurately modelling stellar halo formation on all scales in semi-analytic models.