Spin statistics in binary galaxies : implications for formation and evolution.

September 1984 • 1984ApJ...284..471H

Authors • Helou, G.

Abstract • New data are presented defining unambiguously the spin vectors of spiral galaxies in binaries and small groups. A strong anticorrelation is found, whereby the spins of companion galaxies avoid being parallel and favor being antiparallel. This indicates that the sample contains predominantly true, physically associated pairs. The anticorrelation is stronger for pairs with low indicative mass-to-light ratio: this is taken as additional evidence for the reality of the effect. Clues to the origin of spin in galaxies are also direct clues to the mechanism of galaxy formation. The evidence so far is clearly against a simple picture where primeval turbulence is the source of spin. But the data are consistent with, and suggestive of, the hypothesis that spins were acquired via tidal torquing; a detailed discussion is given, treating separately the possibility that the effect is primordial and the possibility that it is a result of evolution. Enough data are now becoming available that specific calculations are required to sharpen the predictions for the statistical behavior of spins, especially in binaries.

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George Helou

IPAC Executive Director