# Stars, gas, and star formation of distant post-starburst galaxies

**Authors:** Po-Feng Wu, Rachel Bezanson, Francesco D'Eugenio, Anna R. Gallazzi, Jenny E. Greene, Michael V. Maseda, Katherine A. Suess, Arjen van der Wel  
**arXiv:** [2308.08681](https://arxiv.org/abs/2308.08681)  
**Date:** 2023-08-16  
**Summary page:** https://www.summarizepaper.com/en/paper/2308.08681v1/

## Key points

- Study focuses on five poststarburst galaxies with stellar masses > $10^{11} M_\odot$ at redshift ~0.7
- High incidence of companion galaxies and low surface brightness tidal features indicate quenching is related to galaxy interactions
- Progenitors of these galaxies had stellar masses ranging from $2\times10^9 M_\odot$ to $10^{11} M_\odot$
- Burst of star formation occurred several hundred million years prior to observation, with decay time scale of ~100 million years
- ALMA observations detect CO(2-1) emission in four out of the five galaxies studied
- Molecular gas spreads over distances > 1 arcsecond (~10 kiloparsecs) with mass up to ~$2 \times10^{10} M_\odot$
- Star-forming regions within these galaxies are unresolved by slit spectra and 3 GHz continuum observations
- Comparisons suggest low star-forming efficiency in these poststarburst galaxies
- Commonly used calibrations tend to overestimate true values due to radiation from old stars and contributions from AGN
- Weak AGN-driven outflows revealed by optical spectra
- Study provides insights into properties and evolution of high stellar mass poststarburst galaxies

## Summary

This study presents a comprehensive multi-wavelength analysis of five poststarburst galaxies with stellar masses greater than $10^{11} M_\odot$ at a redshift of approximately 0.7. The authors examine the stars, gas, and current and past star-formation activities in these galaxies. Using optical images from the Subaru telescope and Hubble Space Telescope, the authors observe a high incidence of companion galaxies and low surface brightness tidal features, indicating that quenching (the process by which galaxies cease their star formation) is closely related to interactions between galaxies. The authors also analyze optical spectra provided by the LEGA-C survey to model the stellar continuum and derive the star-formation histories of these poststarburst galaxies. They find that the progenitors of these galaxies had stellar masses ranging from $2\times10^9 M_\odot$ to $10^{11} M_\odot$ and underwent a burst of star formation several hundred million years prior to observation, with a decay time scale of approximately 100 million years. Additionally, ALMA observations detect CO(2-1) emission in four out of the five galaxies studied. The molecular gas is found to spread over distances greater than 1 arcsecond (equivalent to approximately 10 kiloparsecs) with a mass reaching up to approximately $2 \times10^{10} M_\odot$. However, despite detecting molecular gas, the authors find that star-forming regions within these galaxies are unresolved by both slit spectra and 3 GHz continuum observations conducted by the Very Large Array. Comparisons between star-formation rates and gas masses as well as sizes of CO emission and star-forming regions suggest a low star-forming efficiency in these poststarburst galaxies. The authors demonstrate that commonly used calibrations based on infrared and radio luminosities tend to overestimate true values due to radiation from old stars and contributions from active galactic nuclei (AGN). Weak AGN-driven outflows are revealed by the optical spectra. In conclusion, this study provides valuable insights into the properties and evolution of poststarburst galaxies with high stellar masses. The findings highlight the importance of galaxy interactions in quenching star formation and emphasize the need for accurate measurements of star-formation rates in order to understand the true nature of these galaxies.