Impact of baryons on the population of Galactic subhalos and implications for dark matter searches

TL;DR

This study uses advanced cosmological simulations to show that baryons significantly reduce the number and alter the properties of Galactic subhalos, impacting dark matter detection strategies.

Contribution

It provides a detailed comparison of subhalo populations in simulations with and without baryons, highlighting their effects on subhalo abundance and concentration.

Findings

Baryons decrease subhalo abundance by a factor of ~2.

Baryons increase subhalo concentration by about 1.5 times.

Results impact dark matter indirect detection and search strategies.

Abstract

We have used Auriga --a set of state-of-the-art cosmological hydrodynamical simulations of Milky Way-size systems-- to study the impact of baryons on the Galactic subhalo population. A DM-only run counterpart of Auriga allows us to compare results with and without baryons. We repopulate the original suites with low-mass subhalos orders of magnitude lighter than the mass resolution limit, starting from a detailed characterization of Auriga data in the well-resolved subhalo mass range. The survival of low-mass subhalos to tidal forces is unclear and under debate nowadays, thus in our study we stay agnostic and consider two different levels of subhalo resilience to tidal stripping ('fragile' and 'resilient' subhalos). We find baryons to alter the Galactic substructure significantly, by decreasing its overall abundance by a factor $\sim2.4$ (fragile) and $\sim1.9$ (resilient) and subhalo concentration --here defined in terms of maximum circular velocity-- by $\sim1.5$ with respect to the DM-only scenario. This has important consequences for indirect searches of DM. As an example, we investigated the case of using unidentified gamma-ray sources to set constraints on the DM particle properties, assuming some of them may be dark satellites. Our results show the importance of including baryons to properly characterize the Galactic subhalo population, as well as to propose the most optimal subhalo search strategies, not only via its potential DM annihilation products but also through their gravitational signatures (e.g.~stellar streams, strong lensing).