The alignment of galaxy spin with the shear field in observations
  Tidal torque theory suggests that galaxies gain angular momentum in the
linear stage of structure formation. Such a theory predicts alignments between
the spin of haloes and tidal shear field. However, non-linear evolution and
angular momentum acquisition may alter this prediction significantly. In this
paper, we use a reconstruction of the cosmic shear field from observed peculiar
velocities combined with spin axes extracted from galaxies within $115\,
\mathrm{Mpc} $ ($\sim8000 \, {\mathrm {km}}{\mathrm s}^{-1}$) from 2MRS
catalog, to test whether or not galaxies appear aligned with principal axes of
shear field. Although linear reconstructions of the tidal field have looked at
similar issues, this is the first such study to examine galaxy alignments with
velocity-shear field. Ellipticals in the 2MRS sample, show a statistically
significant alignment with two of the principal axes of the shear field. In
general, elliptical galaxies have their short axis aligned with the axis of
greatest compression and perpendicular to the axis of slowest compression.
Spiral galaxies show no signal. Such an alignment is significantly strengthened
when considering only those galaxies that are used in velocity field
reconstruction. When examining such a subsample, a weak alignment with the axis
of greatest compression emerges for spiral galaxies as well. This result
indicates that although velocity field reconstructions still rely on fairly
noisy and sparse data, the underlying alignment with shear field is strong
enough to be visible even when small numbers of galaxies are considered -
especially if those galaxies are used as constraints in the reconstruction.
