Title: The Impact of Galaxy Formation on Galaxy Biasing, and Informative Priors for Primordial non-Gaussianity Constraints Speaker: Lucia Perez (Center for Computational Astrophysics, the Flatiron Institute) Date: 2026-05-27 • 03:00 PM - 04:00 PM Location: Sala 300 (M8)

Abstract: The parameter fNL measures the local non-Gaussianity in the primordial energy fluctuations of the Universe, with any deviation from fNL = 0 providing key constraints on inflationary models. Galaxy clustering is sensitive to fNL at large scale modes and the next generation of galaxy surveys will approach a statistical error of σfNL ∼ 1. However, the systematic errors on these constraints are dominated by the degeneracy of fNL with the galaxy bias parameters b1 (galaxy overdensities caused by mass perturbations) and bϕ (galaxy overdensities caused by primordial potential perturbations). It has been shown that the assumed "universality" scaling of bϕ(z) = 2δc(b1(z) − 1) is not accurate for realistically simulated galaxies, and depends both on the galaxy selection and the way that galaxies are modeled. To address this, we leverage the CAMELS-SAM pipeline to explore how varying parameters of galaxy formation affects bϕ and b1 for various galaxy selections. We run separate-universe N-body simulations of L = 205h−1 cMpc and N = 1280^3 to measure bϕ, and run 55 unique instances of the Santa Cruz semi-analytic model with varying parameters of stellar and AGN feedback. We find the behavior and evolution of a SC-SAM model’s stellar-, SFR- and sSFR- to halo mass relationships track well with how b1 and bϕ(b1) change across redshift and selection for the SC-SAM. We find our variations of the SC-SAM encapsulate the bϕ behavior previously measured in IllustrisTNG, the Munich SAM, and Galacticus. Finally, we apply these results to yield informed priors on bϕ conditioned on galaxy observations for fNL measurements.

Read more: https://weiguangcui.github.io/DECAF/blog#2026-05-27