http://arxiv.org/abs/1505.01895
We studied the distribution of projected ellipticity $\epsilon$ for the galaxies in a sample of 20 rich ($\mathcal{R} > 2$) nearby ($z < 0.1$) clusters of galaxies. We find no evidence of differences in the distribution of $\epsilon$ between different clusters, except possibly for the Coma Cluster (the probability that Coma has the same distribution as the other clusters is $P < 10^{-3}$). We then study the distribution of $\epsilon$ within the clusters, and find that $\epsilon$ increases with the projected cluster-centric radius R. The trend is preserved at fixed magnitude, showing that our result exists over and above the trend of more luminous galaxies to be both rounder and more common in the centre of clusters. The trend of $\epsilon$ with R persists even for the subsample of intrinsically flat galaxies ($\epsilon$ > 0.4), therefore it is not a consequence of the increasing fraction of intrinsically round Slow Rotator galaxies nearer the centre of clusters. The trend is also observed for flat, smooth galaxies and dividing the galaxies according to the shape of their light profile. This suggests that the systematic variation of the fraction of spiral galaxies with R does not explain alone the observed trend. We interpret our findings in light of the classification of Early Type Galaxies (ETGs) as Fast and Slow Rotators. We conclude that the observed trend of decreasing $\epsilon$ nearer to the centre of clusters is evidence for physical effects in clusters causing Fast Rotator ETGs to have a lower average intrinsic ellipticity near the centre of rich clusters.
F. DEugenio, R. Houghton, R. Davies, et. al.
Mon, 11 May 15
44/44
Comments: 14 pages, 11 figures, Accepted for publication in MNRAS
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