The large molecular gas fraction of post-starburst galaxies at z > 1

A. Zanella*, F. Valentino, A. Gallazzi, S. Belli, G. Magdis, A. Bolamperti

*Corresponding author for this work

Research output: Contribution to journalJournal articleResearchpeer-review

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Abstract

Post-starburst galaxies are sources that had the last major episode of star formation about 1 Gyr before the epoch of the observations and are on their way to quiescence. It is important to study such galaxies at redshift z > 1, during their main quenching phase, and estimate their molecular gas content to constrain the processes responsible for the cessation of star formation. We present CO(3–2) ALMA observations of two massive (M ∼ 5 × 1010 M) post-starburst galaxies at z > 1. We measure their molecular gas fraction to be fH2 = MH2/M ∼ 8–16 per cent, consistent with z < 1 post-starburst galaxies from the literature. The star formation efficiency of our targets is ∼10× lower than that of star-forming galaxies at similar redshift, and they are outliers of the fH2–specific star formation rate (sSFR) relation of star-forming galaxies, as they have larger fH2 than expected given their sSFR. The gas fraction of post-starbursts from our sample and the literature correlates with the Dn4000 spectral index, a proxy of the stellar population age. This suggests that their gas content decreases after the last major burst of star formation. Finally, one of our targets is undergoing a major merger phase with two highly star-forming companions. This hints at a picture where a perturber event (e.g. major merger) quenches star formation without completely removing the molecular gas.
Original languageEnglish
JournalMonthly Notices of the Royal Astronomical Society
Volume524
Issue number1
Pages (from-to)923-939
ISSN0035-8711
DOIs
Publication statusPublished - 2023

Keywords

  • Galaxies: evolution
  • Galaxies: formation
  • Galaxies: high-redshift
  • Galaxies: ISM

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