Central concentration of asymmetric features in post-starburst galaxies at z ∼ 0.8

Abstract

We present morphological analyses of Post-starburst galaxies (PSBs) at 0.7 < z < 0.9 in the COSMOS field. We fitted ultraviolet to mid-infrared multi-band photometry of objects with i < 24 from COSMOS2020 catalogue with population synthesis models assuming non-parametric, piece-wise constant function of star formation history, and selected 94 those galaxies that have high specific star formation rates (SSFRs) of more than 10−9.5 yr−1 in 321–1000 Myr before observation and an order of magnitude lower SSFRs within recent 321 Myr. We devised a new non-parametric morphological index which quantifies concentration of asymmetric features, CA, and measured it as well as concentration C and asymmetry A on the Hubble Space Telescope /Advanced Camera for Surveys IF814W-band images. While relatively high C and low A values of PSBs are similar with those of quiescent galaxies rather than star-forming galaxies, we found that PSBs show systematically higher values of CA than both quiescent and star-forming galaxies; 36% of PSBs have log CA > 0.8, while only 16% (2%) of quiescent (star-forming) galaxies show such high CA values. Those PSBs with high CA have relatively low overall asymmetry of A ∼ 0.1, but show remarkable asymmetric features near the centre. The fraction of those PSBs with high CA increases with increasing SSFR in 321–1000 Myr before observation rather than residual on-going star formation. These results and their high surface stellar mass densities suggest that those galaxies experienced a nuclear starburst in the recent past, and processes that cause such starbursts could lead to the quenching of star formation through rapid gas consumption, supernova/AGN feedback, and so on.

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

“…Meanwhile, deep and highresolution optical images reveal that post-starburst galaxies tend to be more compact than the typical quiescent galaxies, yet often display disturbed morphologies (Wild et al 2009;Vergani et al 2010;Wu et al 2014Wu et al , 2018Setton et al 2022). This points toward a formation scenario in which quenching in the distant Universe is the result of intense central starbursts brought on by gravitational interactions between galaxies (Wu et al 2020;Himoto & Kajisawa 2023). However, despite such findings, deep rest-frame optical spectroscopy that is resolved spatially does not always find positive stellar age gradients, as one would expect if the central starbursts had happened (D'Eugenio et al 2020;Setton et al 2020).…”