The Impact of Galaxy Formation on Galaxy Biasing, and Implications for Primordial non-Gaussianity Constraints

TL;DR

This paper investigates how galaxy formation models influence galaxy bias parameters relevant for constraining primordial non-Gaussianity, emphasizing the importance of accurate bias modeling for future large-scale structure surveys.

Contribution

The study uses the CAMELS-SAM pipeline and separate-universe simulations to analyze how galaxy formation parameters affect galaxy bias, providing insights for improving primordial non-Gaussianity constraints.

Findings

Galaxy bias parameters vary with galaxy formation model parameters.

sSFR-based galaxy selections are robust to modeling uncertainties.

Results align with previous measurements from other galaxy formation simulations.

Abstract

The parameter $f_{\textrm{NL}}$ measures the local non-Gaussianity in the primordial energy fluctuations of the Universe, with any deviation from $f_{\textrm{NL}}=0$ providing key constraints on inflationary models. Galaxy clustering is sensitive to $f_{\textrm{NL}}$ at large scale modes and the next generation of galaxy surveys will approach a statistical error of $\sigma_{f_{\textrm{NL}}}\sim1$. However, the systematic errors on these constraints are dominated by the degeneracy of $f_{\textrm{NL}}$ with the galaxy bias parameters $b_1$ (galaxy overdensities caused by mass perturbations) and $b_{\phi}$ (galaxy overdensities caused by primordial potential perturbations). It has been shown that the assumed scaling of $b_{\phi}(z)=2\delta_c (b_1(z)-1)$ 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 $b_{\phi}$ and $b_1$ for various galaxy selections. We run separate-universe N-body simulations of $L=205 h^{-1}$ cMpc and $N=1280^3$ to measure $b_{\phi}$, 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 $b_1$ and $b_{\phi}(b_1)$ change across redshift and selection for the SC-SAM. We find our variations of the SC-SAM encapsulate the $b_{\phi}$ behavior previously measured in IllustrisTNG, the Munich SAM, and Galacticus.Finally, we identify sSFR selections as particularly robust to varied galaxy modeling.