# The Nature of Post-Starburst Galaxies: Real Deal or Masquerading Impostors?

## TL;DR

This study uses cosmological simulations to investigate the nature of post-starburst galaxies, revealing that most are impostors with ongoing star formation, and that true PSBs likely result from black hole feedback.

## Contribution

It provides the first detailed simulation-based analysis distinguishing true PSBs from impostors and links true PSBs to black hole feedback mechanisms.

## Key findings

- Only ~10% of simulated PSBs are true PSBs with quenched star formation.
- Most PSBs in simulations are impostors with ongoing star formation.
- Over 70% of true PSBs are predicted to originate from black hole feedback.

## Abstract

Post-starburst galaxies (PSBs) are a population of rapidly quenched galaxies that have experienced a recent starburst. Several aspects of the origin and nature of PSBs are currently debated. For example, some PSBs unexpectedly host substantial molecular gas despite their low star-formation activity. Furthermore, the relative role of galaxy mergers, interaction, and stellar or black hole feedback in the formation of PSBs remains unclear. We investigate the nature of PSBs at z=0.7 and z=1 selected via rest-frame optical photometric properties, using the FIREbox cosmological simulation. The fraction of PSBs in FIREbox is in reasonable agreement with observational estimates. However, only ~10% of PSBs in FIREbox are `true' PSBs with temporarily quenched star-formation activity. Most galaxies selected as PSBs in FIREbox are impostors, having star-formation rates and gas masses that are comparable to those of non-PSB galaxies with similar stellar masses. Furthermore, PSBs rich in molecular gas are almost exclusively impostors. `True' PSBs and impostors differ on average in their mid-to-near infrared ratio but with significant scatter. By combining the impostor frequency among star forming galaxies in FIREbox with observational estimates, we predict that more than 70% of `true' PSBs in the Universe should originate from massive black hole feedback.