We performed B and R band surface photometry for E/S0 galaxies in a nearby rich cluster ABELL 2199 to investigate their B - R color gradients ( d ( B - R ) / d \log r ) .
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 color gradients in elliptical galaxies .
We studied the distribution of the B - R color gradients in the cluster ellipticals and found that the mean value of the color gradients is -0.09 \pm 0.04 mag/dex , which can be converted to a metallicity gradient ( d \log Z / d \log r ) of \sim - 0.3 \pm 0.1 .
The gradient seems to be comparable to that expected by a recent monolithic collapse model .
We further studied the relations between the B - R color gradients and global properties of the galaxies .
Our data suggest that for the galaxies brighter than an R band magnitude of \sim 15 mag , which is roughly equivalent to L ^ { * } at the distance of the cluster , brighter galaxies tend to have steeper color gradients .
Also , for the galaxies with effective radii larger than \sim 3 ^ { \prime \prime } , which nearly corresponds to L ^ { * } considering the correlation between galaxy luminosity and effective radius for elliptical galaxies , the galaxies with larger effective radii seem to have steeper color gradients .
These trends could appear if elliptical galaxies formed through the monolithic collapse scenario .
On the contrary , it is found based on the published data that such trends are not clearly seen for elliptical galaxies in less dense environments , suggesting that elliptical galaxies in sparse environments formed by galaxy mergers , though the distribution of the color gradients is quite similar to that in the rich cluster .
In other words , our data and those in the literature suggest that there is an environmental dependence in the relationship between color gradient and global properties of elliptical galaxies , while the distribution of the values of color gradients is nearly independent of galaxy environment .
These results do not fully support the view that ellipticals in rich clusters formed through the monolithic collapse while those in sparse environments formed through galaxy mergers , because the latter ellipticals are expected to have color gradients shallower on average than the former .
This apparent conflict may be reconciled by taking into account star formation and subsequent chemical enrichment induced by galaxy merger , which may allow a merger remnant to acquire a metallicity gradient and thus compensate the dilution of the existing metallicity gradients in the progenitors by mixture of stars during the galaxy merger .