Baryon-CDM isocurvature galaxy bias with IllustrisTNG [CEA]

http://arxiv.org/abs/1907.04317


We study the impact that baryon-CDM relative density perturbations $\delta_{bc}$ have on galaxy formation using cosmological simulations with the IllustrisTNG model. These isocurvature (non-adiabatic) perturbations originate before baryon-photon decoupling, when baryons did not comove with CDM. The presence of long-wavelength $\delta_{bc}$ perturbations in the simulations is mimicked by modifying the ratios of the cosmic densities of baryons $\Omega_b$ and CDM $\Omega_c$, at fixed total matter density $\Omega_m$. We measure the corresponding galaxy bias parameter $b_{\delta}^{bc}$ as the response of galaxy abundances to $\delta_{bc}$. We find that $b_{\delta}^{bc}$ is negative and that it decreases with halo mass and redshift: for $M_{\rm h} = 10^{13}\ M_{\odot}/h$ we find $b_{\delta}^{bc} = -0.7, -1.5$ at $z = 1,2$, respectively, and at $z=1$ we find $b_{\delta}^{bc} = -0.3,-0.7$ at $M_{\rm h} = 10^{12}, 10^{13}\ M_{\odot}/h$, respectively. Much of the $z$- and $M_{\rm h}$-dependence of $b_{\delta}^{bc}$ can be attributed to the impact that $\Omega_b/\Omega_c$ has on the linear matter power spectrum. We also measure $b_{\delta}^{bc}$ as a function of stellar mass, which we find can be modeled approximately using semi-analytical halo mass function formulae and stellar-to-halo-mass relations. We estimate that the impact of $\delta_{bc}$ on the galaxy power spectrum is not expected to exceed $1\%$ for $M_{\rm h} \approx 10^{12} – 10^{13} M_{\odot}/h$ and $z \lesssim 2$, and that shifts on distance and growth rate parameters inferred from data should be below $0.1\%$ for galaxy samples similar to BOSS DR12.

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A. Barreira, G. Cabass, D. Nelson, et. al.
Wed, 10 Jul 19
38/53

Comments: 17 pages (+6 pages with appendices and references); 6 figures; 2 tables; comments welcomed