Informative Priors on Primordial Non-Gaussianity Bias $b_ϕ$ From Galaxy Formation
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arXiv
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2026
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| author | Moore, Anne Perez, Lucia A. Krause, Elisabeth |
| author_facet | Moore, Anne Perez, Lucia A. Krause, Elisabeth |
| contents | Constraining primordial non-Gaussianity via its scale-dependent imprint on galaxy clustering requires knowledge of the bias parameter $b_ϕ$, which is exactly degenerate with $f^{\rm{loc}}_{\rm{NL}}$ at leading order. To break this degeneracy, current analyses adopt the relation $\left(b_ϕ = 2δ_c\left(b_1 - 1\right)\right)$ based on the assumption of a universal mass function. This relation is known to break down for physically motivated galaxy selections, introducing systematic errors in the inferred $f^{\rm{loc}}_{\rm{NL}}$ that scale directly with the assumed $b_ϕ$ prior. We present a framework to construct physically motivated, observation-conditioned priors on $b_ϕ$ by marginalizing over galaxy formation uncertainties. We use the CAMELS-SAM simulation suite, augmented by separate Universe simulations, to measure galaxy formation observables, like the stellar mass function (SMF) and the stellar-to-halo mass relationship (SHMR), and $b_ϕ$ across a range of galaxy formation parameters. From these measurements, we construct a distribution of $b_ϕ$ conditioned on observations, and we select our galaxy sample to resemble the DESI Emission Line Galaxy (ELG) sample. Conditioning on the SMF or SHMR decreases $σ_{b_ϕ}$ from $0.69$ to $0.08$ and $0.02$ respectively -- reductions of $88\%$ and $97\%$ -- with consistent results when conditioning on the observed data directly. Despite substantial shifts in the galaxy formation posteriors driven by known SC-SAM discrepancies at high halo masses, the resulting $b_ϕ$ distributions remain mutually consistent across all observables. The SMF and SHMR are found to carry sufficient constraining power to reduce the galaxy formation uncertainty in $b_ϕ$ relevant for $f^{\rm{loc}}_{\rm{NL}}$ inference with next-generation spectroscopic surveys |
| format | Preprint |
| id |
arxiv_https___arxiv_org_abs_2604_21790 |
| institution | arXiv |
| publishDate | 2026 |
| record_format | arxiv |
| spellingShingle | Informative Priors on Primordial Non-Gaussianity Bias $b_ϕ$ From Galaxy Formation Moore, Anne Perez, Lucia A. Krause, Elisabeth Cosmology and Nongalactic Astrophysics Constraining primordial non-Gaussianity via its scale-dependent imprint on galaxy clustering requires knowledge of the bias parameter $b_ϕ$, which is exactly degenerate with $f^{\rm{loc}}_{\rm{NL}}$ at leading order. To break this degeneracy, current analyses adopt the relation $\left(b_ϕ = 2δ_c\left(b_1 - 1\right)\right)$ based on the assumption of a universal mass function. This relation is known to break down for physically motivated galaxy selections, introducing systematic errors in the inferred $f^{\rm{loc}}_{\rm{NL}}$ that scale directly with the assumed $b_ϕ$ prior. We present a framework to construct physically motivated, observation-conditioned priors on $b_ϕ$ by marginalizing over galaxy formation uncertainties. We use the CAMELS-SAM simulation suite, augmented by separate Universe simulations, to measure galaxy formation observables, like the stellar mass function (SMF) and the stellar-to-halo mass relationship (SHMR), and $b_ϕ$ across a range of galaxy formation parameters. From these measurements, we construct a distribution of $b_ϕ$ conditioned on observations, and we select our galaxy sample to resemble the DESI Emission Line Galaxy (ELG) sample. Conditioning on the SMF or SHMR decreases $σ_{b_ϕ}$ from $0.69$ to $0.08$ and $0.02$ respectively -- reductions of $88\%$ and $97\%$ -- with consistent results when conditioning on the observed data directly. Despite substantial shifts in the galaxy formation posteriors driven by known SC-SAM discrepancies at high halo masses, the resulting $b_ϕ$ distributions remain mutually consistent across all observables. The SMF and SHMR are found to carry sufficient constraining power to reduce the galaxy formation uncertainty in $b_ϕ$ relevant for $f^{\rm{loc}}_{\rm{NL}}$ inference with next-generation spectroscopic surveys |
| title | Informative Priors on Primordial Non-Gaussianity Bias $b_ϕ$ From Galaxy Formation |
| topic | Cosmology and Nongalactic Astrophysics |
| url | https://arxiv.org/abs/2604.21790 |