  We present direct constraints on galaxy intrinsic alignments using the Dark
Energy Survey Year 3 (DES Y3), the Extended Baryon Oscillation Spectroscopic
Survey (eBOSS) and its precursor, the Baryon Oscillation Spectroscopic Survey
(BOSS). Our measurements incorporate photometric red sequence (redMaGiC)
galaxies from DES with median redshift $z\sim0.2-1.0$, luminous red galaxies
(LRGs) from eBOSS at $z\sim0.8$, and also a SDSS-III BOSS CMASS sample at
$z\sim0.5$. We measure two point intrinsic alignment correlations, which we fit
using a model that includes lensing, magnification and photometric redshift
error. Fitting on scales $6<r_{\rm p} < 70$ Mpc$/h$, we make a detection of
intrinsic alignments in each sample, at $5\sigma-22\sigma$ (assuming a simple
one parameter model for IAs). Using these red samples, we measure the
IA-luminosity relation. Our results are statistically consistent with previous
results, but offer a significant improvement in constraining power,
particularly at low luminosity. With this improved precision, we see detectable
dependence on colour between broadly defined red samples. It is likely that a
more sophisticated approach than a binary red/blue split, which jointly
considers colour and luminosity dependence in the IA signal, will be needed in
future. We also compare the various signal components at the best fitting point
in parameter space for each sample, and find that magnification and lensing
contribute $\sim2-18\%$ of the total signal. As precision continues to improve,
it will certainly be necessary to account for these effects in future direct IA
measurements. Finally, we make equivalent measurements on a sample of Emission
Line Galaxies (ELGs) from eBOSS at $z\sim 0.8$. We report a null detection,
constraining the IA amplitude (assuming the nonlinear alignment model) to be
$A_1=0.07^{+0.32}_{-0.42}$ ($|A_1|<0.78$ at $95\%$ CL).

Cosmology and Nongalactic Astrophysics