Advances in Constraining Intrinsic Alignment Models with Hydrodynamic Simulations
Abstract
We use galaxies from the IllustrisTNG, MassiveBlackII and Illustris hydrodynamic simulations to investigate the behaviour of large scale galaxy intrinsic alignments. Our analysis spans four redshift slices over the approximate range of contemporary lensing surveys $z=01$. We construct comparable weighted samples from the three simulations, which we then analyse using an alignment model that includes both linear and quadratic alignment contributions. Our data vector includes galaxygalaxy, galaxyshape and shapeshape projected correlations, with the joint covariance matrix estimated analytically. In all of the simulations, we report nonzero IAs at the level of several $\sigma$. For a fixed lower mass threshold, we find a relatively strong redshift dependence in all three simulations, with the linear IA amplitude increasing by a factor of $\sim 2$ between redshifts $z=0$ and $z=1$. We report no significant evidence for nonzero values of the tidal torquing amplitude, $A_2$, in TNG, above statistical uncertainties, although MassiveBlackII favours a moderately negative $A_2\sim2$. Examining the properties of the TATT model as a function of colour, luminosity and galaxy type (satellite or central), our findings are consistent with the most recent measurements on real data. We also outline a novel method for constraining the TATT model parameters directly from the pixelised tidal field, alongside a proof of concept exercise using TNG. This technique is shown to be promising, although the comparison with previous results obtained via other methods is nontrivial.
 Publication:

arXiv eprints
 Pub Date:
 September 2020
 arXiv:
 arXiv:2009.10735
 Bibcode:
 2020arXiv200910735S
 Keywords:

 Astrophysics  Cosmology and Nongalactic Astrophysics
 EPrint:
 28 pages, 18 Figures