Constraints on intrinsic alignment contamination of weak lensing surveys
  using the MegaZ-LRG sample
  Correlations between the intrinsic shapes of galaxies and the large-scale
galaxy density field provide an important tool to investigate galaxy intrinsic
alignments, which constitute a major astrophysical systematic in cosmological
weak lensing (cosmic shear) surveys, but also yield insight into the formation
and evolution of galaxies. We measure galaxy position-shape correlations in the
MegaZ-LRG sample for more than 800,000 luminous red galaxies, making the first
such measurement with a photometric redshift sample. In combination with a
re-analysis of several spectroscopic SDSS samples, we constrain an intrinsic
alignment model for early-type galaxies over long baselines in redshift (z ~
0.7) and luminosity (4mag). We develop and test the formalism to incorporate
photometric redshift scatter in the modelling. For r_p > 6 Mpc/h, the fits to
galaxy position-shape correlation functions are consistent with the scaling
with r_p and redshift of a revised, nonlinear version of the linear alignment
model for all samples. An extra redshift dependence proportional to (1+z)^n is
constrained to n=-0.3+/-0.8 (1sigma). To obtain consistent amplitudes for all
data, an additional dependence on galaxy luminosity proportional to L^b with
b=1.1+0.3-0.2 is required. The normalisation of the intrinsic alignment power
spectrum is found to be (0.077 +/- 0.008)/rho_{cr} for galaxies at redshift 0.3
and r band magnitude of -22 (k- and evolution-corrected to z=0). Assuming zero
intrinsic alignments for blue galaxies, we assess the bias on cosmological
parameters for a tomographic CFHTLS-like lensing survey. Both the resulting
mean bias and its uncertainty are smaller than the 1sigma statistical errors
when using the constraints from all samples combined. The addition of MegaZ-LRG
data reduces the uncertainty in intrinsic alignment bias on cosmological
parameters by factors of three to seven. (abridged)
