Large-Field Multicolor Study of A168: Subclusters, Dynamics, and Luminosity Functions

This paper presents a multicolor study of the nearby cluster of galaxies A168 (z = 0.045) with 13 intermediate-band filters in the Beijing-Arizona-Taiwan-Connecticut (BATC) filter system. After a cross-identification between the photometric data obtained from the BATC and the Sloan Digital Sky Survey (SDSS), a catalog containing 1553 galaxies down to r′ < 20.0 mag is achieved, which includes 121 spectroscopically confirmed member galaxies. The technique of photometric redshift has been applied to all these galaxies with combined 18 band (13 from BATC and five from SDSS) spectral energy distributions (SEDs), in order to perform a faint membership selection in A168. As a result, 255 galaxies are newly selected as the member candidates. On the basis of the enlarged sample of cluster galaxies, the spatial distribution and dynamics of A168 are investigated. In light of the spatial distribution of the member galaxies and the 0.2-3.5 keV X-ray image by the Einstein X-Ray Observatory, it seems that A168 consists of two merging subclusters with a relative radial velocity of 264 ± 142 km s-1. With the help of ROSTAT software, a detailed investigation of the dynamics shows the intrinsic difference in the velocity distributions for these two subclusters. Under a linear two-body model, they are found to be a gravitationally bound system with 92% probability. The slight deviation of the local velocity distribution from the overall distribution in the central region may suggest a picture of head-on collision in the projection plane. By using a double Schechter function, the close examination of the luminosity functions reveals the different galaxy content of these two subclusters, which implies that the merging process is possibly at the early stage.