The role of accreted and in situ populations in shaping the stellar halos of low-mass galaxies

TL;DR

This study uses high-resolution cosmological simulations to analyze the composition, formation, and evolution of stellar halos in low-mass dwarf galaxies, highlighting the roles of in-situ formation and accretion processes.

Contribution

It provides a detailed characterization of stellar halos in simulated dwarf galaxies, revealing the dominance of in-situ material in low-mass galaxies and the impact of accretion history on halo formation.

Findings

Inner stellar halos are dominated by in-situ material.

Less massive dwarfs have in-situ dominance at all radii.

More massive dwarfs' halos are mainly accreted beyond 6 times the half-light radius.

Abstract

The stellar halos of dwarf galaxies are becoming an object of interest in the extragalactic community due to their detection in some recent observations. Additionally, new cosmological simulations of very high resolution were performed, allowing their study. These stellar halos could help shed light on our understanding of the assembly of dwarf galaxies and their evolution, and allow us to test the hierarchical model for the formation of structures at small scales. We aim to characterise the stellar halos of simulated dwarf galaxies and analyse their evolution and accretion history. We use a sample of 17 simulated galaxies from the Auriga Project with a stellar mass range from 3.28x10^8 Msun to 2.08x10^10 Msun. We define the stellar halo as the stellar material located outside an ellipsoid with semi-major axes equal to 4 times the half light radius (Rh) of each galaxy. We find that the inner regions of the stellar halo (4 to 6 times the Rh) are dominated by in-situ material. For the less massive simulated dwarfs (M*<=4.54x10^8 Msun), this dominance extends to all radii. We find that this in-situ stellar halo is mostly formed in the inner regions of the galaxies and then ejected into the outskirts during interactions and merger events. In ~50% of the galaxies, the stripped gas from satellites contributed to the formation of this in-situ halo. The stellar halos of the galaxies more massive than M*>=1x10^9 Msun are dominated by the accreted component beyond 6 Rh. We find that the more massive dwarf galaxies accrete stellar material until later times (t90~4.44 Gyr ago, being t90 the formation time) than the less massive ones (t90~8.17 Gyr ago), impacting on the formation time of the accreted stellar halos. The galaxies have a range of 1 to 7 significant progenitors contributing to their accreted component but there is no correlation between this quantity and the galaxies' accreted mass.