BaryonCDM isocurvature galaxy bias with IllustrisTNG
Abstract
We study the impact that baryonCDM relative density perturbations $\delta_{bc}$ have on galaxy formation using cosmological simulations with the IllustrisTNG model. These isocurvature (nonadiabatic) perturbations originate before baryonphoton decoupling, when baryons did not comove with CDM. The presence of longwavelength $\delta_{bc}$ 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 semianalytical halo mass function formulae and stellartohalomass 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.
 Publication:

arXiv eprints
 Pub Date:
 July 2019
 arXiv:
 arXiv:1907.04317
 Bibcode:
 2019arXiv190704317B
 Keywords:

 Astrophysics  Cosmology and Nongalactic Astrophysics;
 Astrophysics  Astrophysics of Galaxies
 EPrint:
 17 pages (+6 pages with appendices and references)