POSITION ANGLES AND ALIGNMENTS OF CLUSTERS OF GALAXIES

The position angles of a large number of Abell and Shectman clusters, identified in the Lick map as surface galaxy-density enhancements, are estimated. I determine the major axis orientation of a total of 637 clusters, of which 448 are Shectman clusters (202 of which are also Abell clusters) and 189 are Abell clusters not originally detected by Shectman due to his adopted density threshold. Using published redshifts for 277 of these clusters I have detected strong nearest neighbor alignments over scales up to similar to 15 h(-1) Mpc at a greater than or similar to 2.5-3 sigma significance level, while quite weak alignments are detected even up to similar to 60 h(-1) Mpc. A more significant alignment signal (similar to 4 sigma) is detected among all neighbors residing in superclusters and having separations less than or similar to 10 h(-1) Mpc. Again, weaker but significant alignments are found when larger separations are considered. Since my cluster sample is neither volume limited nor redshift complete (which would have tended to wash out any real alignment signal), the alignments detected should reflect a real and possibly a stronger underline effect.