Dark Energy Survey Year 1 Results: Constraints on Intrinsic Alignments
  and their Colour Dependence from Galaxy Clustering and Weak Lensing
  We perform a joint analysis of intrinsic alignments and cosmology using
tomographic weak lensing, galaxy clustering and galaxy-galaxy lensing
measurements from Year 1 (Y1) of the Dark Energy Survey. We define early- and
late-type subsamples, which are found to pass a series of systematics tests,
including for spurious photometric redshift error and point spread function
correlations. We analyse these split data alongside the fiducial mixed Y1
sample using a range of intrinsic alignment models. In a fiducial Nonlinear
Alignment Model (NLA) analysis, assuming a flat \lcdm~cosmology, we find a
significant difference in intrinsic alignment amplitude, with early-type
galaxies favouring $A_\mathrm{IA} = 2.38^{+0.32}_{-0.31}$ and late-type
galaxies consistent with no intrinsic alignments at $0.05^{+0.10}_{-0.09}$. We
find weak evidence of a diminishing alignment amplitude at higher redshifts in
the early-type sample. The analysis is repeated using a number of extended
model spaces, including a physically motivated model that includes both tidal
torquing and tidal alignment mechanisms. In multiprobe likelihood chains in
which cosmology, intrinsic alignments in both galaxy samples and all other
relevant systematics are varied simultaneously, we find the tidal alignment and
tidal torquing parts of the intrinsic alignment signal have amplitudes $A_1 =
2.66 ^{+0.67}_{-0.66}$, $A_2=-2.94^{+1.94}_{-1.83}$, respectively, for
early-type galaxies and $A_1 = 0.62 ^{+0.41}_{-0.41}$, $A_2 =
-2.26^{+1.30}_{-1.16}$ for late-type galaxies. In the full (mixed) Y1 sample
the best constraints are $A_1 = 0.70 ^{+0.41}_{-0.38}$, $A_2 = -1.36
^{+1.08}_{-1.41}$. For all galaxy splits and IA models considered, we report
cosmological parameter constraints that are consistent with the results of
Troxel et al. (2017) and Dark Energy Survey Collaboration (2017).
