Statistical separation of weak gravitational lensing and intrinsic
  ellipticities based on galaxy colour information
  Intrinsic alignments of galaxies are recognised as one of the most important
systematic in weak lensing surveys on small angular scales. In this paper we
investigate ellipticity correlation functions that are measured separately on
elliptical and spiral galaxies, for which we assume the generic alignment
mechanisms based on tidal shearing and tidal torquing, respectively. Including
morphological information allows to find linear combinations of measured
ellipticity correlation functions which suppress the gravitational lensing
signal completely or which show a strongly boosted gravitational lensing signal
relative to intrinsic alignments. Specifically, we find that $(i)$ intrinsic
alignment spectra can be measured in a model-independent way at a significance
of $\Sigma\simeq 60$ with a wide-angle tomographic survey such as Euclid's,
$(ii)$ intrinsic alignment model parameters can be determined at percent-level
precision, $(iii)$ this measurement is not impeded by misclassifying galaxies
and assuming a wrong alignment model, $(iv)$ parameter estimation from a
cleaned weak lensing spectrum is possible with almost no bias and $(v)$ the
misclassification would not strongly impact parameter estimation from the
boosted weak lensing spectrum.
