Assembly bias in the local PNG halo bias and its implication for fNL constraints

Titouan Lazeyras, Alexandre Barreira, Fabian Schmidt, Vincent Desjacques

Submitted on 15 September 2022


We use N-body simulations to study halo assembly bias (i.e., the dependence of halo clustering on properties beyond total mass) in the density and primordial non-Gaussianity (PNG) linear bias parameters b1 and bϕ, respectively. We consider concentration, spin and sphericity as secondary halo properties, for which we find a clear detection of assembly bias for b1 and bϕ. At fixed total mass, halo spin and sphericity impact b1 and bϕ in a similar manner, roughly preserving the shape of the linear bϕ(b1) relation satisfied by the global halo population. Halo concentration, however, drives b1 and bϕ in opposite directions. This induces significant changes to the bϕ(b1) relation, with higher concentration halos having higher amplitude of bϕ(b1). For z=0.5 and b12 in particular, the population comprising either all halos, those with the 33% lowest or those with the 33% highest concentrations have a PNG bias of bϕ3, bϕ1 and bϕ9, respectively. Varying the halo concentration can make bϕ very small and even change its sign. These results have important ramifications for galaxy clustering constraints of the local PNG parameter fNL that assume fixed forms for the bϕ(b1) relation. We illustrate the significant impact of halo assembly bias in actual data using the BOSS DR12 galaxy power spectrum: assuming that BOSS galaxies are representative of all halos, the 33% lowest or the 33% highest concentration halos yields σfNL=44,165,19, respectively. Our results suggest taking host halo concentration into account in galaxy selection strategies to maximize the signal-to-noise on fNL. They also motivate more simulation-based efforts to study the bϕ(b1) relation of halos and galaxies.


Comment: 21 pages, 4 figures, comments welcome

Subject: Astrophysics - Cosmology and Nongalactic Astrophysics