A Catalog of Distant Compact Groups Using DPOSS
  In this paper we present an objectively defined catalog of 459 small, high density groups of galaxies out to z~0.2 in a region of 6260 square degrees in the northern sky derived from the Digitized Second Palomar Observatory Sky Survey. Our catalog extends down to r = 19.0 and has a median redshift of z_med = 0.12, making it complementary to Hickson's catalog for the nearby universe (z_med = 0.03). The depth and angular coverage of this catalog makes it valuable for studies of the general characteristics of small groups of galaxies and how galaxies evolve in and around them. We also examine the relationship between compact groups and large scale structure. 
R. R. de Carvalho, T. S. Goncalves, A. Iovino, J. L. Kohl-Moreira, R.   R. Gal and S. G. Djorgovski