Calibrating Galaxy Infall Times in Groups and Clusters with IllustrisTNG Simulations

TL;DR

This paper develops a redshift-dependent method to estimate galaxy infall times in groups and clusters using simulations, enabling better understanding of environmental effects on galaxy evolution.

Contribution

It introduces a simple, observationally applicable prescription for infall time based on phase space position and stellar mass, derived via symbolic regression from simulations.

Findings

Provides a continuous estimate of infall time across phase space.

Offers analytic expressions for characteristic infall timescales.

Framework applicable to spectroscopic galaxy samples.

Abstract

The time since a galaxy first became a satellite is central to understanding how environment drives galaxy evolution, yet it cannot be measured directly. Using the TNG300 and TNG-Cluster simulations, we track satellites from $z=1$ to $z=0$ and derive a simple, redshift-dependent prescription for ${T}_{\rm{inf}}$ based on position in projected phase space and stellar mass, via symbolic regression. The resulting calibration provides continuous, observation-ready estimates of infall time across projected phase space. In projected phase space, ${T}_{\rm{inf}}$ is often well described by two components, and we provide analytic expressions for the corresponding characteristic timescales. This framework can be applied directly to spectroscopic samples to infer environmental histories in galaxy groups and clusters.