Mathematics – Logic
Scientific paper
Jan 1994
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1994phdt........33c&link_type=abstract
Thesis (PH.D.)--CORNELL UNIVERSITY, 1994.Source: Dissertation Abstracts International, Volume: 54-10, Section: B, page: 5200.
Mathematics
Logic
7
Dark Matter, Cosmology
Scientific paper
Dynamics of pairs of spiral galaxies selected from redshift catalogs is studied in two parts, (1) wide pairs for which HI redshifts were obtained at Arecibo and Parkes, (2) close pairs which were imaged in HI at the VLA and the R and V bands at Palomar. Galaxy pairs were chosen only from regions of low galaxy density. The wide pairs have projected separations of up to 1.0 Mpc, almost an order of magnitude larger than earlier studies. Several samples which differ only in the isolation criteria used are analyzed. The close pairs sample was chosen in an objective way, independent of known morphological peculiarities. The velocity difference distribution for the sample of isolated wide pairs of galaxies decreases monotonically with increasing velocity difference; the peak near 70 km s^{-1} seen in earlier samples is not present, confirming the suggestion that the non-monotonocity of earlier velocity difference distributions is a consequence of a selection bias. The distribution of Delta V for galaxy pairs in low density regions has two components, a peak around zero and a tail extending to larger velocity differences. As the isolation criterion is made more stringent, pairs are preferentially lost from the tail, the width of the peak around zero is little affected by the isolation criterion. The median velocity difference for the isolated wide pairs sample is ~30 km s ^{-1}, less than half the typical velocity difference found in previous studies using compact pairs. Dynamical mass estimators give values of up to a few times 1012 M odot. Tidal disturbances for the six close pairs are consistent with the pairs having started out on high eccentricity, low energy orbits. Direct orbits are found to cause heavy damage to the galaxy's disk with the formation of a pronounced tail and bridge, while retrograde orbits cause less disruption of the galaxy disk. The characteristic Delta V of close pairs is small as compared to that for earlier samples of non-interacting binary galaxies (with similar projected separations). The infall velocity of interacting pairs is hence reduced from free fall values, perhaps due to dynamical friction arising from massive halos.
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