Separate Universe calibration of the dependence of halo bias on cosmic web anisotropy

Abstract: We use the Separate Universe technique to calibrate the dependence of linear and quadratic halo bias $b_1$ and $b_2$ on the local cosmic web environment of dark matter haloes. We do this by measuring the response of halo abundances at fixed mass and cosmic web tidal anisotropy $\alpha$ to an infinite wavelength initial perturbation. We augment our measurements with an analytical framework developed in earlier work which exploits the near-Lognormal shape of the distribution of $\alpha$ and results in very high precision calibrations. We present convenient fitting functions for the dependence of $b_1$ and $b_2$ on $\alpha$ over a wide range of halo mass for redshifts $0\leq z\leq1$. Our calibration of $b_2(\alpha)$ is the first demonstration to date of the dependence of non-linear bias on the local web environment. Motivated by previous results which showed that $\alpha$ is the primary indicator of halo assembly bias for a number of halo properties beyond halo mass, we then extend our analytical framework to accommodate the dependence of $b_1$ and $b_2$ on any such secondary property which has, or can be monotonically transformed to have, a Gaussian distribution. We demonstrate this technique for the specific case of halo concentration, finding good agreement with previous results. Our calibrations will be useful for a variety of halo model analyses focusing on galaxy assembly bias, as well as analytical forecasts of the potential for using $\alpha$ as a segregating variable in multi-tracer analyses.