Dark haloes in Karachentsev's sample of binary galaxies

Tuorla Observatory, University of Turku, 21500 Piikkiö, Finland

Received: 1 February 2001
Accepted: 9 March 2001

Abstract

Karachentsev's sample of 585 compact binary galaxies is inspected in order to see a signature of extended massive dark haloes around the component galaxies. Our approach utilizes the good velocity-separation resolution provided by this sample containing many close pairs, in order to see directly the expected trends in the vs. X_proj plane. A developed version of Turner's normalization, attempting to take into acount different sizes of binary orbits (increasing with luminosity), makes it possible to see "directly" a meaningful lower limit of from the emerging short-projection envelope in the vs. X_norm diagram. This part of the diagram is little influenced by the incompleteness at large values of separation X_proj, which usually leads to too small values of mass-to-luminosity ratios. We conclude that these binaries give relatively direct evidence for the existence of massive dark haloes, with (conservatively) larger than about 25 (for km s^-1/Mpc), consistent with the simulation studies on Karachentsev's triplets by Chernin & Mikkola ([CITE]) and on the binaries by Wiren et al. ([CITE]), and other more recent studies of the triplets (Karachentsev [CITE]).