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In order to investigate the relative orientations of spiral galaxies in pairs, the distribution of the angle between the spin-vectors for a new sample of 40 binary spiral galaxies is determined. From this distribution it is found, contrary to an earlier result obtained by Helou (1984), that there is no indication of a correlation between the orientations of spiral galaxies in pairs. Also the distributions of the relative position angles for a sample of pairs are determined. The data disagree with a simple model for isolated pairs based on tidal torques. A division of the sample into isolated and less-isolated pairs suggests that this disagreement is due to insufficient dynamical isolation during galaxy formation.

The magnitude of the orbital angular momentum is compared with that of the internal angular momentum of the galaxies for our sample as a whole. We find that the orbital angular momentum is typically 4 times larger than the internal angular momentum. This is interpreted as an indication that the pairs in this sample were not dynamically isolated at the time they formed and that this is the reason why no correlation between the spin-vectors is observed. We suggest that pairs for which the spin-vectors were correlated had low orbital angular momentum and have merged. Consequently, studying the relative orientation of the spin-vectors in present day binary spiral galaxies will not give strong constraints on the models for the origin of galactic angular momentum.

Originele taal-2English
Pagina's (van-tot)389-399
Aantal pagina's11
TijdschriftAstronomy & astrophysics
Nummer van het tijdschrift2
StatusPublished - mei-1993

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