BaryonCDM isocurvature galaxy bias with IllustrisTNG
Abstract
We study the impact that baryonCDM relative density perturbations δ_{bc} have on galaxy formation using cosmological simulations with the IllustrisTNG model. These isocurvature (nonadiabatic) perturbations can be induced primordially, if multiple fields are present during inflation, and are generated before baryonphoton decoupling when baryons did not comove with CDM. The presence of longwavelength δ_{bc} perturbations in our simulations is mimicked by modifying the ratios of the cosmic densities of baryons Ω_{b} and CDM Ω_{c}, at fixed total matter density Ω_{m}. We measure the corresponding galaxy bias parameter b_{δ}^{bc} as the response of galaxy abundances to δ_{bc}. When selecting by total host halo mass, b_{δ}^{bc} is negative and it decreases with mass and redshift. Stellarmass selected simulated galaxies show a weaker or even the opposite trend because of the competing effects of δ_{bc} on the halo mass function and stellartohalomass relations. We show that simple modeling of the latter two effects describes b_{δ}^{bc} for stellarmassselected objects well. We find b_{δ}^{bc} =0.6 for M_{*} = 10^{11} M_{solar}/h and z=0.5, which is representative of BOSS DR12 galaxies. For δ_{bc} modes generated by baryonphoton interactions, we estimate the impact on the DR12 power spectrum to be below 1%, and shifts on inferred distance and growth rate parameters should not exceed 0.1%.
 Publication:

Journal of Cosmology and Astroparticle Physics
 Pub Date:
 February 2020
 DOI:
 10.1088/14757516/2020/02/005
 arXiv:
 arXiv:1907.04317
 Bibcode:
 2020JCAP...02..005B
 Keywords:

 Astrophysics  Cosmology and Nongalactic Astrophysics;
 Astrophysics  Astrophysics of Galaxies
 EPrint:
 18 pages (+8 pages with appendices and references)