Predictions for local PNG bias in the galaxy power spectrum and bispectrum and the consequences for f _{NL} constraints
Abstract
We use hydrodynamical separate universe simulations with the IllustrisTNG model to predict the local primordial nonGaussianity (PNG) bias parameters b _{ϕ} and b _{ϕδ}, which enter at leading order in the galaxy power spectrum and bispectrum. This is the first time that b _{ϕδ} is measured from either gravityonly or galaxy formation simulations. For dark matter halos, the popular assumption of universality overpredicts the b _{ϕδ}(b _{1}) relation in the range 1 ≲ b _{1} ≲ 3 by up to Δ b _{ϕδ} ~ 3 (b _{1} is the linear density bias). The adequacy of the universality relation is worse for the simulated galaxies, with the relations b _{ϕ}(b _{1}) and b _{ϕδ}(b _{1}) being generically redshiftdependent and very sensitive to how galaxies are selected (we test total, stellar and black hole mass, black hole mass accretion rate and color). The uncertainties on b _{ϕ} and b _{ϕδ} have a direct, often overlooked impact on the constraints of the local PNG parameter f _{NL}, which we study and discuss. For a survey with V = 100 Gpc^{3}/h^{3} at z=1, uncertainties Δ b _{ϕ} ≲ 1 and Δ b _{ϕδ} ≲ 5 around values close to the fiducial can yield relatively unbiased constraints on f _{NL} using power spectrum and bispectrum data. We also show why priors on galaxy bias are useful even in analyses that fit for products f _{NL} b _{ϕ} and f _{NL} b _{ϕδ}. The strategies we discuss to deal with galaxy bias uncertainties can be straightforwardly implemented in existing f _{NL} constraint analyses (we provide fits for some of the bias relations). Our results motivate more works with galaxy formation simulations to refine our understanding of b _{ϕ} and b _{ϕδ} towards improved constraints on f _{NL}.
 Publication:

Journal of Cosmology and Astroparticle Physics
 Pub Date:
 January 2022
 DOI:
 10.1088/14757516/2022/01/033
 arXiv:
 arXiv:2107.06887
 Bibcode:
 2022JCAP...01..033B
 Keywords:

 cosmological parameters from LSS;
 cosmological simulations;
 hydrodynamical simulations;
 redshift surveys;
 Astrophysics  Cosmology and Nongalactic Astrophysics
 EPrint:
 18 pages + 2 appendices