On the origin of intrinsic alignment in cosmic shear measurements: an
  analytic argument
  Galaxy intrinsic alignment can be a severe source of error in weak-lensing
studies. The problem has been widely studied by numerical simulations and with
heuristic models, but without a clear theoretical justification of its origin
and amplitude. In particular, it is still unclear whether intrinsic alignment
of galaxies is dominated by formation and accretion processes or by the effects
of the instantaneous tidal field acting upon them. We investigate this question
by developing a simple model of intrinsic alignment for elliptical galaxies,
based on the instantaneous tidal field. Making use of the galaxy stellar
distribution function, we estimate the intrinsic alignment signal and find that
although it has the expected dependence on the tidal field, it is too weak to
account for the observed signal. This is an indirect validation of the standard
view that intrinsic alignment is caused by formation and/or accretion
processes.
