Galaxy Zoo: building the low-mass end of the red sequence with local post-starburst galaxies

TL;DR

This study investigates local post-starburst galaxies using SDSS data and Galaxy Zoo classifications, revealing their role in building the low-mass end of the red sequence and supporting the downsizing galaxy evolution model.

Contribution

It provides new insights into the morphology and evolutionary path of low-mass PSGs, linking them to the formation of the red sequence in galaxy evolution.

Findings

Most PSGs are neither early- nor late-type morphologies.

PSGs occupy the low-mass green valley region.

PSGs likely evolve into low-mass red early-type galaxies.

Abstract

We present a study of local post-starburst galaxies (PSGs) using the photometric and spectroscopic observations from the Sloan Digital Sky Survey (SDSS) and the results from the Galaxy Zoo project. We find that the majority of our local PSG population have neither early- nor late- type morphologies but occupy a well-defined space within the colour-stellar mass diagram, most notably, the low-mass end of the "green valley" below the transition mass thought to be the mass division between low-mass star-forming galaxies and high-mass passively-evolving bulge-dominated galaxies. Our analysis suggests that it is likely that a local PSG will quickly transform into "red", low-mass early-type galaxies as the stellar morphologies of the "green" PSGs largely resemble that of the early-type galaxies within the same mass range. We propose that the current population of PSGs represents a population of galaxies which is rapidly transitioning between the star-forming and the passively-evolving phases. Subsequently, these PSGs will contribute towards the build-up of the low-mass end of the "red sequence" once the current population of young stars fade and stars are no longer being formed. These results are consistent with the idea of "downsizing" where the build-up of smaller galaxies occurs at later epochs.