Substructure in the stellar halos of the Aquarius simulations

TL;DR

This paper analyzes the substructure of stellar halos in the Aquarius simulations, revealing tidal features and anisotropic distributions that resemble observations, and discusses implications for the Milky Way's formation history.

Contribution

It provides a detailed characterization of substructures in simulated stellar halos, highlighting their similarity to observed features and exploring their implications for galaxy formation.

Findings

Stellar halos exhibit tidal features similar to the Milky Way.

Substructures are anisotropically distributed on the sky.

Possible in-situ star formation in the Milky Way halo.

Abstract

We characterize substructure in the simulated stellar halos of Cooper et al. (2010) which were formed by the disruption of satellite galaxies within the cosmological N-body simulations of galactic halos of the Aquarius Project. These stellar halos exhibit a wealth of tidal features: broad overdensities and very narrow faint streams akin to those observed around the Milky Way. The substructures are distributed anisotropically on the sky, a characteristic that should become apparent in the next generation of photometric surveys. The normalized RMS of the density of stars on the sky appears to be systematically larger for our halos compared to the value estimated for the Milky Way from main sequence turn-off stars in the Sloan Digital Sky Survey. We show that this is likely to be due in part to contamination by faint QSOs and redder main sequence stars, and might suggest that ~10% of the Milky Way halo stars have formed in-situ.