Merger Signatures are Common, but not Universal, in Massive, Recently Quenched Galaxies at z ∼ 0.7

Abstract

We present visual classifications of merger-induced tidal disturbances in 143 M * ∼ 1011 M ⊙ post-starburst galaxies at z ∼ 0.7 identified in the SQuIGG L ⃗ E Sample. This sample spectroscopically selects galaxies from the Sloan Digital Sky Survey that have stopped their primary epoch of star formation within the past ∼500 Myr. Visual classifications are performed on Hyper Suprime-Cam imaging. We compare to a control sample of mass- and redshift-matched star-forming and quiescent galaxies from the Large Early Galaxy Census and find that post-starburst galaxies are more likely to be classified as disturbed than either category. This corresponds to a factor of 3.6 − 1.3 + 2.9 times the disturbance rate of older quiescent galaxies and 2.1 − .73 + 1.9 times the disturbance rate of star-forming galaxies. Assuming tidal features persist for ≲500 Myr, this suggests merging is coincident with quenching in a significant fraction of these post-starbursts. Galaxies with tidal disturbances are younger on average than undisturbed post-starburst galaxies in our sample, suggesting tidal features from a major merger may have faded over time. This may be exacerbated by the fact that, on average, the undisturbed subset is fainter, rendering low-surface-brightness tidal features harder to identify. However, the presence of 10 young (≲150 Myr since quenching) undisturbed galaxies suggests that major mergers are not the only fast physical mechanism that shut down the primary epoch of star formation in massive galaxies at intermediate redshift.

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

“…They also point out that most disturbances are low-surface brightness features which require high sensitivity and fine spatial resolution to be identified, and that fade in short time-scales, suggesting that all their post-SBs might have had a merger origin. Similar results are also found by Verrico et al ( 2023 ), who also show that post-SBs are 3 . 6 + 2 .…”

Stars, Gas, and Star Formation of Distant Post-starburst Galaxies

“…Out of the five galaxies we observed, four exhibit disturbed morphologies as seen through either HST or HSC imaging. The high incident rate of disturbed features is consistent with the observation from ∼100 massive post-starburst galaxies at similar redshift by Verrico et al (2023). The residual star formation, if present, appears to be centralized around the galactic cores (Figure 5).…”