Multicolor Photometry of the Galaxy Cluster A98: Substructures and Star Formation Properties

TL;DR

This study uses multicolor optical photometry to analyze the galaxy cluster A98, revealing its substructures, member galaxies, and environmental effects on star formation, supporting hierarchical galaxy formation models.

Contribution

It provides a detailed analysis of A98's substructures and star formation properties using multicolor photometry and photometric redshifts, which is novel for this cluster.

Findings

Identification of three substructures: A98N, A98S, A98W.

Discovery of a separate galaxy group A98X.

Environmental effects on star formation histories of member galaxies.

Abstract

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.