Datensatz

Zusammenfassung

We study the impact that baryon-CDM relative density perturbations δ_bc have on galaxy formation using cosmological simulations with the IllustrisTNG model. These isocurvature (non-adiabatic) perturbations can be induced primordially, if multiple fields are present during inflation, and are generated before baryon-photon decoupling when baryons did not comove with CDM. The presence of long-wavelength 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. Stellar-mass 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 stellar-to-halo-mass relations. We show that simple modeling of the latter two effects describes b_δ^bc for stellar-mass-selected objects well. We find b_δ^bc =0.6 for M_* = 10¹¹ M_⊙/h and z=0.5, which is representative of BOSS DR12 galaxies. For δ_bc modes generated by baryon-photon 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%.