Did all local post-starburst galaxies quench through the same pathway? (2025)
Post-starburst (PSB) galaxies are galaxies that have recently (0.5-2Gyr) experienced a period of increased star formation, followed by rapid quenching. They are not very common (~1% in the local universe at log10(M*/Msol)>9.5), but because we are catching them right after they quenched, they are very useful in trying to see if we can observe some of the left over signs from what caused them to quench, which helps us understand the drivers of galaxy quenching.
However, the observational picture becomes a bit more complex. Since we started observing PSB galaxies with integrated field spectroscopy (IFS, spatially resolved spectroscopy across the galaxy), we have noticed PSBs with different spatial distributions in where the stars are actually PSB-like. Chen et al. (2019) classified SDSS MaNGA galaxies into central PSBs (PSB regions centrally concentrated or covers the whole galaxy), ring PSBs (PSB regions form a ring around the centre, which could be star forming or quiescent) and irregular PSBs. Then, the next logical question to ask is:
Do PSBs with different spatial distributions of PSB regions have different origins with distinct quenching mechanisms? Or are they driven by the same quenching mechanisms, but are in different stages of the same process?
To try to answer the above question, we repeated the analysis in Leung et al. (2024) also on the PSB regions of ring PSB galaxies (the 2024 paper was on the PSB regions of central PSB galaxies). We found that despite their different positions in their respective galaxies, the PSB regions have very similar star-formation and stellar metallicity histories (see below). We conclude this suggests that all PSB regions are regulated by a common set of local scale processes in the inter stellar medium, regardless of the broader quenching triggering mechanism.
We also took the central regions encircled by the PSB regions in ring PSBs, and studied their properties in relation to the outer PSB ring. We find that vast majority of these central regions are also quenching, far quicker than the average central region in mass- and redshift-matched control main sequence galaxies.
Correlating the recent star-formation histories of the central regions to the ring PSB regions, we found diverse origin among ring PSBs. We propose the population can be split into four types (see below), with the majority reflecting a stage of a global quenching process. The main difference depends on whether the centre began quenching earlier, later or at the same time as the outer regions, and if it is quenching quicker, slower or at the same speed. Some of these types can evolve from or into central PSBs, i.e. different stages of the same process, but only a small fraction is likely to do so. We finally speculate what could be the physical mechanisms that caused each of these ring PSB types.