The STAGES view of red spirals and dusty red galaxies: Mass-dependent quenching of star-formation in cluster infall

TL;DR

This study examines red spirals and dusty red galaxies in a galaxy cluster at redshift 0.17, revealing their significant star formation activity, mass-dependent quenching processes, and implications for galaxy evolution.

Contribution

It provides new insights into the properties and quenching mechanisms of red spirals and dusty red galaxies, emphasizing their role in cluster star formation and morphological transformation.

Findings

Red spirals and dusty red galaxies are largely the same phenomenon.

Star formation in these galaxies is only four times lower than in blue spirals at fixed mass.

Quenching is slow for massive galaxies and rapid with morphological change for less massive ones.

Abstract

We investigate the properties of optically passive spirals and dusty red galaxies in the A901/2 cluster complex at redshift ~0.17 using restframe near-UV-optical SEDs, 24 micron IR data and HST morphologies from the STAGES dataset. The cluster sample is based on COMBO-17 redshifts with an rms precision of sigma_cz~2000 km/sec. We find that 'dusty red galaxies' and 'optically passive spirals' in A901/2 are largely the same phenomenon, and that they form stars at a substantial rate, which is only 4x lower than that in blue spirals at fixed mass. This star formation is more obscured than in blue galaxies and its optical signatures are weak. They appear predominantly in the stellar mass range of log M*/Msol=[10,11] where they constitute over half of the star-forming galaxies in the cluster; they are thus a vital ingredient for understanding the overall picture of star formation quenching in clusters. We find that the mean specific SFR of star-forming galaxies in the cluster is clearly lower than in the field, in contrast to the specific SFR properties of blue galaxies alone, which appear similar in cluster and field. Such a rich red spiral population is best explained if quenching is a slow process and morphological transformation is delayed even more. At log M*/Msol<10, such galaxies are rare, suggesting that their quenching is fast and accompanied by morphological change. We note, that edge-on spirals play a minor role; despite being dust-reddened they form only a small fraction of spirals independent of environment.