The Role of Mass and Environment on Satellite distributions around Milky Way analogs in the Romulus25 simulation

TL;DR

This study uses the Romulus25 simulation to analyze how host galaxy mass and environment influence satellite galaxy counts and quenching, revealing that larger hosts and denser environments tend to have more satellites and higher quenched fractions.

Contribution

It provides a comprehensive analysis of satellite populations around Milky Way analogs in a large cosmological simulation, highlighting the roles of host mass and environment, and compares findings with observational surveys.

Findings

Satellite counts increase with host stellar mass.

Higher-density environments correlate with increased satellite quenched fractions.

Potentially higher quenched fractions in galaxy pairs versus isolated systems.

Abstract

We study satellite counts and quenched fractions for satellites of Milky Way analogs in Romulus25, a large-volume cosmological hydrodynamic simulation. Depending on the definition of a Milky Way analog, we have between 66 and 97 Milky Way analogs in Romulus25, a 25 Mpc per-side uniform volume simulation. We use these analogs to quantify the effect of environment and host properties on satellite populations. We find that the number of satellites hosted by a Milky Way analog increases predominantly with host stellar mass, while environment, as measured by the distance to a Milky Way-mass or larger halo, may have a notable impact in high isolation. Similarly, we find that the satellite quenched fraction for our analogs also increases with host stellar mass, and potentially in higher-density environments. These results are robust for analogs within 3 Mpc of another Milky Way-mass or larger halo, the environmental parameter space where the bulk of our sample resides. We place these results in the context of observations through comparisons to the Exploration of Local VolumE Satellites and Satellites Around Galactic Analogs surveys. Our results are robust to changes in Milky Way analog selection criteria, including those that mimic observations. Finally, as our samples naturally include Milky Way-Andromeda pairs, we examine quenched fractions in pairs vs isolated systems. We find potential evidence, though not conclusive, that pairs, defined as being within 1 Mpc of another Milky Way-mass or larger halo, may have higher satellite quenched fractions.