What is the Small-Scale Velocity Dispersion of Galaxy Pairs?

Original · EN

We present some new results from an ongoing investigation of the anisotropy of the two--point correlation function for optically selected galaxies. We have estimated xi(rₚ,pi) from the Perseus-Pisces redshift survey, which is now virtually 100% complete for all morphological types to mB = 15.5. We detect strong distortions of the iso-correlation contours in xi(rₚ,pi). These correspond to a global (`cluster' plus `field') pairwise velocity dispersion at 1 h⁻¹ Mpc, sigma(1), which is about a factor of two higher than the canonical value 350 km s⁻¹ obtained from the CfA1 survey and recently from the 1.2 Jy IRAS redshift survey. However, the variance of this value is still rather strong even within the relatively large volumes surveyed (typically 90∘ × 45∘ × 100 h⁻¹ Mpc). From the largest volume explorable (126 h⁻¹ Mpc depth), the best bet for the `cosmic' value of sigma(1) seems to be between 600 and 700 km s⁻¹. However, for a hopefully robust determination of its value we will have to wait for the analyses of the next generation of larger optical redshift surveys (such as, e.g., the now completed ESP or the forthcoming Sloan Digital Sky Survey).