Accreted mass and stellar haloes in isolated galaxies from TNG50
We study the accreted mass and stellar haloes of ~5000 isolated galaxies with virial masses log(M_200/M_sun) > 10.3 from the hydrodynamic cosmological simulation TNG50-1. We find a strong correlation between the mass fraction of these components and virial mass, particularly in the dwarf regime, while the correlation with stellar mass is weaker. Ex-situ stars comprise 60-100% of the stellar halo mass, representing less than 1% of the total stellar mass of the galaxy. At a fixed virial mass, the median age and characteristic size of the accreted component decrease with increasing accreted mass. Stacked surface density profiles demonstrate that the accreted component is well-described by a Sérsic profile, with the Sérsic index correlating with the excess accreted mass at a given virial mass. Galaxies below the median accreted mass exhibit n = 2.0±0.5, while those above the median are better fit by n = 3.5±0.5, with a mild increase at higher masses. These results provide predictions for stellar halo properties in galaxies less massive than the Milky Way, enabling comparison with observations. Our findings suggest that analysing the oldest stars in galactic outskirts offers valuable insights into galaxy assembly history across a broad mass range.
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Accreted mass and stellar haloes in isolated galaxies from TNG50