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

We present our optical multicolor photometry for the nearby cluster ofgalaxies Abell 2255 with 13 intermediate filters in the BATC system. Thespectral energy distributions (SEDs) in the optical band for more than 7000sources are achieved down to V ~ 20 in a field of 58' x 58' centered on thisrich cluster. Abell 2255 has been recently observed by the SDSS. A method ofcombining the SDSS photometric data in five broad bands and the BATC SEDs isthen explored. The application of the technique of photometric redshift showsthat the combined SEDs with higher resolution could lead to a more accurateestimate of photometric redshift. Based on 214 spectroscopically confirmedmember galaxies, the bimodality and large dispersion in the velocitydistribution indicate that Abell 2255 is an unrelaxed system. A tightcolor-magnitude correlation for 188 known early-type cluster galaxies is found.After an exclusion of 254 extragalactic sources with known redshifts, thecombined SEDs for 2522 galaxies allow a further membership selection by thephotometric redshift technique and color-magnitude correlation. As a result,313 galaxies with their photometric redshifts between 0.068 and 0.090 areselected as new cluster members. The combined SEDs and estimated redshifts forpreviously known and newly-selected member galaxies are cataloged. On the basisof the enlarged sample of member galaxies, the spatial distribution, localizedvelocity structure, color-magnitude relation, and luminosity function ofcluster galaxies are discussed. The reverse peculiar velocities are found fortwo satellite subclusters located on opposite sides of the centralconcentration, which supports an ongoing merger in Abell 2255.Comment: 37 pages, including 13 figures and 6 tables, Accepted by the ApJ