Poster Title: Colour Gradients in Elliptical Galaxies : Environmental Dependence of Formation History ?
Abstract: We investigated B-R colour gradients in 29 E/S0 galaxies in a nearby rich cluster ABELL 2199. Our aims are to study statistical properties of the color gradients and, by comparing them with those in less dense environments, to examine environmental dependence of colour gradients in elliptical galaxies.
We found that the mean value of the colour gradients is -0.09 +- 0.04 mag/dex in d(B-R)/dlogr, which can be converted to a metallicity gradient of ~ -0.3 in dlogZ/dlogr assuming an old stellar population. Our data also suggest that for the galaxies brighter than $L_*$, more luminous and larger galaxies tend to have steeper colour gradients. The typical value of the colour gradients seems to be consistent with a recent monolithic collapse model and the correlation could also appear if elliptical galaxies formed through the monolithic collapse.
On the contrary, it is found based on data from the literature that any such trend between galaxy luminosity or size and colour gradient is clearly weaker for elliptical galaxies in less dense environments, though the distribution of the values of colour gradient is quite similar to that found in the rich cluster. Based on the results from our data and the published data, formation process of elliptical galaxy and its environmental dependence will be discussed.
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