GALAXY PAIRS, REDSHIFT CATALOGS, AND THE COSMIC PECULIAR VELOCITY

We discuss pairs of spiral galaxies with projected separations r(p) ra nging from very wide (r(p) similar to 1.0 Mpc) to very small (r(p) les s than or similar to 75 kpc). Single-dish H I data for the wide pairs and H I aperture synthesis as well as CCD images for the close pairs w ere presented in earlier papers.From pairs (regardless of isolation cr iteria) in redshift catalogs, we find that the kinematics of spiral-sp iral pairs in low-density regions is qualitatively different from that in high-density regions. The velocity distribution function f(Delta V ) in low-density regions has two components: (i) a narrow component (w hich is related to isolated pairs) with a very small rms value sigma(u psilon,n) of the ''one-dimensional random cosmic peculiar velocity'' d elta upsilon, and (ii) a broad, slowly decreasing component (which is related to pairs in loose groups) with a large rms value of the ''one- dimensional random cosmic peculiar velocity'' sigma(upsilon,b). Thus, we confirm that the distribution of the ''one-dimensional cosmic pecul iar velocity'' delta upsilon is not Gaussian and its rms value a, vari es with environment. The median Delta V-med of the absolute value of t he velocity difference of isolated wide pairs is similar to 30 km s(-1 ), considerably smaller than all estimates of sigma(upsilon). This sma ll Delta V-med suggests that the pairs are on low total energy, almost radial orbits, and it is also a constraint on cosmological models of structure formation. We find some circumstantial evidence for a negati ve correlation between the peculiar velocity delta upsilon and the dif ferential Hubble flow velocity Delta V-H which would be the case for b ound orbits near the maximum separation (''turnaround'') at the curren t epoch. If future larger samples (e.g., the CfA2 and the SSRS2 survey s) confirm this, then a total galaxy mass similar to 10(12) M. is impl ied. All the six close pairs for which we have detailed H I and optica l CCD images show some signs of interaction, even though the selection criteria were specifically independent of known morphological peculia rities. For three of the six pairs there is good evidence for the pair s also being on high eccentricity, low total energy orbits, and there is some evidence that the impact parameter for one pair is similar to 1 disk radius. The median velocity difference Delta V-med, of the clos e pairs sample is also similar to 30 km s(-1). This small value of Del ta V-med is probably an indirect effect of dynamical friction.