2007ApJ...671.1248L

We report direct observational evidence for the existence of the galaxy spin alignments with the real-space tidal field. We calculate the real-space tidal field from the real-space density field reconstructed recently from the 2MASS Redshift Survey (2MRS) by Erdogdu et al. in 2006. Using a total of 12,122 nearby spiral galaxies from the Tully Galaxy Catalog, we calculate the orientations of their spin axes relative to the 2MRS tidal field. We find a clear signal of the intrinsic correlations between the galaxy spins and the intermediate principal axes of the tidal shears. The null hypothesis of no correlation is rejected at 99.99% confidence level. We also investigate the dependence of the intrinsic correlations on the galaxy morphological type and the environment. It is found that (1) the intrinsic correlation depends weakly on the morphological type of the spiral galaxies, but tends to decrease slightly as the type increases; and (2) it is stronger in the high-density regions than in the low-density regions. The observational result is quantitatively consistent with analytic prediction based on the tidal torque theory. It is concluded that the galaxy spin orientations may provide in principle a new complimentary probe of the dark matter distribution.