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Slow quenching of star formation in OMEGAWINGS clusters: galaxies in transition in the local universe

, , , , , , , , , , and .
(2015)cite arxiv:1512.04549.

Abstract

The star formation quenching depends on environment, but a full understanding of what mechanisms drive it is still missing. Exploiting a sample of galaxies with masses $M_\ast>10^9.8M_ødot$, drawn from the WIde-field Nearby Galaxy-cluster Survey (WINGS) and its recent extension OMEGAWINGS, we investigate the star formation rate (SFR) as a function of stellar mass (M$_*$) in galaxy clusters at $0.04<z<0.07$. We use non-member galaxies at 0.02$<$z$<$0.09 as field control sample. Overall, we find agreement between the SFR-M$_*$ relation in the two environments, but detect a population of cluster galaxies with reduced SFRs which is rare in the field. These transition galaxies are mainly found within the cluster virial radius ($R_200$) but they impact on the SFR-M$_*$ relation only within 0.6R$_200$. The ratio of transition to PSF galaxies strongly depends on environment, being larger than 0.6 within 0.3R$_200$ and rapidly decreasing with distance, while it is almost flat with $M_*$. As galaxies move downward from the SFR-M$_*$ main sequence, they become redder and present older luminosity and mass weighted ages. These trends, together with the analysis of the star formation histories, suggest that transition galaxies have had a reduced SFR for the past 2-5 Gyr. Our results are consistent with the hypothesis that the interaction of galaxies with the intracluster medium via strangulation causes a gradual shut down of star formation, giving birth to an evolved population of galaxies in transition from being star forming to becoming passive.

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