A catalog of UGC isolated galaxy pairs with accurate radial velocities

Abstract

The present paper is devoted to the construction of a catalog of isolated galaxy pairs from the Uppsala Galaxy Catalog (UGC), using accurate radial velocities. The UGC lists 12921 galaxies to declination larger than -2 deg 30 min and is complete to an apparent diameter of 1 arcmin. The criteria used to define the isolated galaxy pairs are the following: 1) Velocity criterion: radial velocity difference between the members lower than 500 km/s; 2) Interdistance criterion: projected distance between the members smaller than 1 Mpc; 3) Reciprocity criterion: each member is the closest galaxy to the other one, which excludes multiplets; 4) Isolation information: the catalog lists the ratio between the projected distance to the closest UGC galaxy (having a velocity difference smaller than 500 km/s) and the pair members interdistance, thus allowing one to choose any isolation criterion (beyond the chosen limit 2.5). In addition, we have accounted for the small diameter bias by searching for CGCG galaxies in the pair environment and used the same isolation criterion. A peculiar investigation has allowed to gather very accurate radial velocities for pair members, from high quality HI and optical measurements (median uncertainty on velocity differences 10 km/s). Our final catalog contains 1005 galaxy pairs. Then we give some global properties of the pair catalog. We display the histograms of the radial velocity differences between the pair members and of their projected interdistances (median 0.29 Mpc). Finally, we provide an estimate of the contamination by cosmological false "pairs", which is about 10 percent up to a velocity difference of 380 km/s, beyond which all pairs are probably false.