Post-starburst Galaxies in SDSS-IV MaNGA: Two Broad Categories of Evolutionary Pathways

Abstract

We study the size–mass relation (SMR) and recent star formation history (SFH) of post-starburst (PSB) galaxies in the local Universe using spatially resolved spectroscopy from the final data release of MaNGA. Our sample includes 489 PSB galaxies: 94 cPSB galaxies with central PSB regions, 85 rPSB galaxies with ringlike PSB regions, and 310 iPSB galaxies with irregular PSB regions. When compared to control galaxies of similar star formation rate, redshift, and mass, a similar SMR is found for all types of PSB samples except the cPSB galaxies, which have smaller sizes at intermediate masses ( 9.5≲log10(M*/M⊙)≲10.5 ). The iPSB galaxies in the star-forming sequence (iPSB-SF) show no/weak gradients in D n (4000), EW(Hδ A ), and EW(Hα), consistent with the global star-forming status of this type of galaxy, while the quiescent iPSB (iPSB-Q) sample shows negative gradients in D n (4000) and positive gradients in EW(Hδ A ), indicating older stellar populations in the inner regions. Both the cPSB and rPSB samples show positive gradients in D n (4000) and negative gradients in EW(Hδ A ), indicating younger stellar populations in the inner regions. These results imply that the four types of PSB galaxies can be broadly divided into two distinct categories in terms of evolutionary pathway: (1) iPSB-SF and iPSB-Q, which have SMRs and SFHs similar to control galaxies, preferring an inside-out quenching process, and (2) rPSB and cPSB, which appear to be different stages of the same event and likely to follow the outside-in quenching process driven by disruption events such as mergers that result in a more compact structure as quenching proceeds.