Are All Post-starbursts Mergers? HST Reveals Hidden Disturbances in the Majority of PSBs

Elizaveta Sazonova, Katherine Alatalo, Kate Rowlands, Susana E. Deustua, K. Decker French, Timothy Heckman, Lauranne Lanz, Ute Lisenfeld, Yuanze Luo, Anne Medling, Kristina Nyland, Justin A. Otter, Andreea O. Petric, Gregory F. Snyder, Claudia Megan Urry

Research output: Contribution to journalArticlepeer-review


How do galaxies transform from blue, star-forming spirals to red, quiescent early-type galaxies? To answer this question, we analyzed a set of 26 gas-rich, shocked post-starburst galaxies with Hubble Space Telescope (HST) imaging in B, I, and H bands and Sloan Digital Sky Survey (SDSS) i-band imaging of similar depth but lower resolution. We found that post-starbursts in our sample have intermediate morphologies between disk- and bulge-dominated (Sérsic) and have red bulges, likely due to dust obscuration in the cores. A majority of galaxies in our sample are more morphologically disturbed than regular galaxies (88%, corresponding to >3σ significance) when observed with HST, with asymmetry and Sérsic residual flux fraction being the most successful measures of disturbance. Most disturbances are undetected at the lower resolution of SDSS imaging. Although ∼27% galaxies are clear merger remnants, we found that disturbances in another ∼30% of the sample are internal, caused by small-scale perturbations or dust substructures rather than tidal features, and require high-resolution imaging to detect. We found 2.8σ evidence that asymmetry features fade on timescales ∼200 Myr, and may vanish entirely after ∼750 Myr, so we do not rule out a possible merger origin of all post-starbursts given that asymmetric features may have already faded. This work highlights the importance of small-scale disturbances, detected only in high-resolution imaging, in understanding structural evolution of transitioning galaxies.

Original languageEnglish (US)
Article number134
JournalAstrophysical Journal
Issue number2
StatePublished - Oct 1 2021

ASJC Scopus subject areas

  • Astronomy and Astrophysics
  • Space and Planetary Science


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