Multicolor Photometry of the Galaxy Cluster A98: Substructures and Star
  Formation Properties
  An optical photometric observation with the
Beijing-Arizona-Taiwan-Connecticut (BATC) multicolor system is carried out for
A98 (z=0.104), a galaxy cluster with two large enhancements in X-ray surface
brightness. The spectral energy distributions (SEDs) covering 15 intermediate
bands are obtained for all sources detected down to V ~ 20 mag in a field of
$58' \times 58'$. After the star-galaxy separation by the color-color diagrams,
a photometric redshift technique is applied to the galaxy sample for further
membership determination. The color-magnitude relation is taken as a further
restriction of the early-type cluster galaxies. As a result, a list of 198
faint member galaxies is achieved. Based on newly generated sample of member
galaxies, the dynamical substructures, A98N, A98S, and A98W, are investigated
in detail. A separate galaxy group, A98X, is also found to the south of main
concentration of A98, which is gravitationally unbound to A98. For 74
spectroscopically confirmed member galaxies, the environmental effect on the
star formation histories is found. The bright galaxies in the core region are
found to have shorter time scales of star formation, longer mean stellar ages,
and higher metallicities of interstellar medium, which can be interpreted in
the context of hierarchical cosmological scenario.
