Optically-passive spirals: The missing link in gradual star formation suppression upon cluster infall

TL;DR

This paper identifies a population of optically passive, blue spiral galaxies in cluster infall regions, revealing a gradual star formation suppression process that links blue spirals to S0 galaxies, distinct from merger or AGN effects.

Contribution

It demonstrates that environmental effects cause a slow quenching of star formation, producing optically faint red spirals as a transitional phase in galaxy evolution.

Findings

Large numbers of red spirals found in cluster infall regions.

Star formation suppression occurs gradually, not via mergers or AGN.

Red spirals evolve into S0 galaxies, indicating a slow quenching process.

Abstract

Galaxies migrate from the blue cloud to the red sequence when their star formation is quenched. Here, we report on galaxies quenched by environmental effects and not by mergers or strong AGN as often invoked: They form stars at a reduced rate which is optically even less conspicuous, and manifest a transition population of blue spirals evolving into S0 galaxies. These 'optically passive' or 'red spirals' are found in large numbers in the STAGES project (and by Galaxy Zoo) in the infall region of clusters and groups.