Quenching of satellite galaxies of Milky Way analogues: reconciling theory and observations

TL;DR

This study compares cosmological simulations with observations of satellite galaxies around Milky Way-like hosts, revealing that differences in host mass and observational biases explain the apparent discrepancy in star formation activity.

Contribution

It demonstrates that accounting for host mass distributions and observational selection effects reconciles simulation predictions with observed satellite galaxy properties.

Findings

SAGA satellites are biased towards recently accreted, star-forming, high surface brightness galaxies.

Deeper surveys show pronounced quenching at low masses, aligning with LCDM simulations.

Differences in host mass and observational biases explain the apparent discrepancy.

Abstract

The vast majority of low-mass satellite galaxies around the Milky Way and M31 appear virtually devoid of cool gas and show no signs of recent or ongoing star formation. Cosmological simulations demonstrate that such quenching is expected and is due to the harsh environmental conditions that satellites face when joining the Local Group (LG). However, recent observations of Milky Way analogues in the SAGA survey present a very different picture, showing the majority of observed satellites to be actively forming stars, calling into question the realism of current simulations and the typicality of the LG. Here we use the ARTEMIS suite of high-resolution cosmological hydrodynamical simulations to carry out a careful comparison with observations of dwarf satellites in the LG, SAGA, and the Local Volume (LV) survey. We show that differences between SAGA and the LG and LV surveys, as well as between SAGA and the ARTEMIS simulations, can be strongly reduced by considering differences in the host mass distributions and (more importantly) observational selection effects, specifically that low-mass satellites which have only recently been accreted are more likely to be star-forming, have a higher optical surface brightness, and are therefore more likely to be included in the SAGA survey. This picture is confirmed using data from the deeper LV survey, which shows pronounced quenching at low masses, in accordance with the predictions of LCDM-based simulations.