Effects of galactic environment on size and dark matter content in low-mass galaxies

TL;DR

This study uses cosmological simulations to show that a galaxy's environment significantly influences its size and dark matter content, with tidal forces and halo mass playing key roles in low-mass galaxy evolution.

Contribution

It demonstrates the combined impact of environment and halo mass on galaxy size and dark matter content using a large simulation dataset and machine learning analysis.

Findings

Galaxies with stronger tidal influences are larger and less dark matter dominated.

Environmental factors and halo mass are both significant predictors of galaxy properties.

Environmental effects on halo mass indirectly influence galaxy size and dark matter content.

Abstract

We utilize the cosmological volume simulation, FIREbox, to investigate how a galaxy's environment influences its size and dark matter content. Our study focuses on approximately 1,200 galaxies (886 central and 332 satellite halos) in the low-mass regime, with stellar masses between $10^6$ to $10^9$ $M_{\odot}$. We analyze the size-mass relation ($r_{50} - M_{\star}$), inner dark matter mass-stellar mass ($M^{50}_{\rm DM} - M_{\star}$) relation, and the halo mass-stellar mass ($M_{\rm halo} - M_{\star}$) relation. At fixed stellar mass, we find the galaxies experiencing stronger tidal influences, indicated by higher Perturbation Indices (PI $>$ 1) are generally larger and have lower masses relative to their counterparts with lower Perturbation Indices (PI $<$ 1). Applying a Random Forest regression model, we show that both the environment (PI) and halo mass ($M_{rm halo}$) are significant predictors of a galaxy's relative size and dark matter content. Notably, because $M_{\rm halo}$ is also strongly affected by the environment, our findings indicate that environmental conditions not only influence galactic sizes and relative inner dark matter content directly, but also indirectly through their impact on halo mass. Our results highlight a critical interplay between environmental factors and halo mass in shaping galaxy properties, affirming the environment as a fundamental driver in galaxy formation and evolution.