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 the major potential 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 for comoving transverse separations of 0.3 < r _ { p } < 60 h ^ { -1 } Mpc , 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 \lesssim 0.7 ) and luminosity ( 4 mag ) with high statistical precision .

We develop and test the formalism to incorporate photometric redshift scatter in the modelling of these observations .
For r _ { p } > 6 h ^ { -1 } Mpc , 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 ( Hirata & Seljak 2004 ) for all samples .
An extra redshift dependence \propto ( 1 + z ) ^ { \eta _ { other } } is constrained to \eta _ { other } = -0.3 \pm 0.8 ( 1 \sigma ) .
To obtain consistent amplitudes for all data , an additional dependence on galaxy luminosity \propto L ^ { \beta } with \beta = 1.1 ^ { +0.3 } _ { -0.2 } is required .
The normalisation of the intrinsic alignment power spectrum is found to be ( 0.077 \pm 0.008 ) \rho _ { cr } ^ { -1 } 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 given our new constraints on the intrinsic alignment model parameter space .
Both the resulting mean bias and its uncertainty are smaller than the 1 \sigma statistical errors when using the constraints from all samples combined .
The addition of MegaZ-LRG data is critical to achieving constraints this strong , reducing the uncertainty in intrinsic alignment bias on cosmological parameters by factors of three to seven .