Multicolor Photometry of the Merging Galaxy Cluster A2319: Dynamics and
  Star Formation Properties
  Asymmetric X-ray emission and powerful cluster-scale radio halo indicate that
A2319 is a merging cluster of galaxies. This paper presents our multicolor
photometry for A2319 with 15 optical intermediate filters in the
Beijing-Arizona-Taiwan-Connecticut (BATC) system. There are 142 galaxies with
known spectroscopic redshifts within the viewing field, including 128 member
galaxies (called sample I).A large velocity dispersion in the rest frame
suggests a merger dynamics in A2319. The contour map of projected density and
localized velocity structure confirm the so-called A2319B substructure, at ~
10' NW to the main concentration A2319A. The spectral energy distributions
(SEDs) of more than 30,000 sources are obtained in our BATC photometry down to
V ~ 20 mag. With color-color diagrams and photometric redshift technique, 233
galaxies brighter than h=19.0 are newly selected as member candidates. The
early-type galaxies are found to follow a tight color-magnitude correlation.
Based on sample I and the enlarged sample of member galaxies (called sample
II), subcluster A2319B is confirmed. A strong environmental effect on star
formation histories is found in the manner that galaxies in the sparse regions
have various star formation histories, while galaxies in the dense regions are
found to have shorter SFR time scales, older stellar ages, and higher ISM
metallicities. For the merging cluster A2319, local surface density is a better
environmental indicator rather than the clustercentric distance. Compared with
the well-relaxed cluster A2589, a higher fraction of star-forming galaxies is
found in A2319, indicating that the galaxy-scale turbulence stimulated by the
subcluster merger might have played a role in triggering the star formation
activity.
