Multicolor Photometry of the Galaxies in A2255 by the Beijing‐Arizona‐Taiwan‐Connecticut Survey and Sloan Digital Sky Survey

Abstract

We present our optical multicolor photometry for the nearby cluster of galaxies Abell 2255 with 13 intermediate filters in the BATC system. The spectral energy distributions (SEDs) in the optical band for more than 7000 sources are achieved down to V ~ 20 in a field of 58' x 58' centered on this rich cluster. Abell 2255 has been recently observed by the SDSS. A method of combining the SDSS photometric data in five broad bands and the BATC SEDs is then explored. The application of the technique of photometric redshift shows that the combined SEDs with higher resolution could lead to a more accurate estimate of photometric redshift. Based on 214 spectroscopically confirmed member galaxies, the bimodality and large dispersion in the velocity distribution indicate that Abell 2255 is an unrelaxed system. A tight color-magnitude correlation for 188 known early-type cluster galaxies is found. After an exclusion of 254 extragalactic sources with known redshifts, the combined SEDs for 2522 galaxies allow a further membership selection by the photometric redshift technique and color-magnitude correlation. As a result, 313 galaxies with their photometric redshifts between 0.068 and 0.090 are selected as new cluster members. The combined SEDs and estimated redshifts for previously known and newly-selected member galaxies are cataloged. On the basis of the enlarged sample of member galaxies, the spatial distribution, localized velocity structure, color-magnitude relation, and luminosity function of cluster galaxies are discussed. The reverse peculiar velocities are found for two satellite subclusters located on opposite sides of the central concentration, which supports an ongoing merger in Abell 2255.