We study the impact that large-scale perturbations of (i) the matter density and (ii) the primordial gravitational potential with local primordial non-Gaussianity (PNG) have on galaxy formation using the IllustrisTNG model. We focus on the linear galaxy bias $b_1$ and the coefficient $b_\phi$ of the scale-dependent bias induced by PNG, which describe the response of galaxy number counts to these two types of perturbations, respectively. We perform our study using separate universe simulations, in which the effect of the perturbations is mimicked by changes to the cosmological parameters: modified cosmic matter density for $b_1$ and modified amplitude $\mathcal{A}_s$ of the primordial scalar power spectrum for $b_\phi$. We find that the widely used universality relation $b_\phi = 2\delta_c(b_1 - 1)$ is a poor description of the bias of haloes and galaxies selected by stellar mass $M_*$, which is instead described better by $b_\phi(M_*) = 2\delta_c(b_1(M_*) - p)$ with $p \in [0.4, 0.7]$. This is explained by the different impact that matter overdensities and local PNG have on the median stellar-to-halo-mass relation. A simple model of this impact allows us to describe the stellar mass dependence of $b_1$ and $b_\phi$ fairly well. Our results also show a nontrivial relation between $b_1$ and $b_\phi$ for galaxies selected by color and black hole mass accretion rate. Our results provide refined priors on $b_\phi$ for local PNG constraints and forecasts using galaxy clustering. Given that the widely used universality relation underpredicts $b_\phi(M_*)$, existing analyses may underestimate the true constraining power on local PNG.

中文翻译：

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星系偏差和原始非高斯性：使用 IllustrisTNG 模拟星系形成的见解

我们使用 IllustrisTNG 模型研究 (i) 物质密度和 (ii) 具有局部原始非高斯性 (PNG) 的原始引力势的大规模扰动对星系形成的影响。我们关注由PNG引起的线性星系偏差$b_1$和尺度相关偏差的系数$b_\phi$，它们分别描述了星系数量计数对这两种扰动的响应。我们使用单独的宇宙模拟进行研究，其中通过宇宙学参数的变化来模拟扰动的影响：$b_1$ 的修正宇宙物质密度和原始标量功率谱的修正振幅 $\mathcal{A}_s$对于 $b_\phi$。我们发现广泛使用的普遍性关系 $b_\phi = 2\delta_c(b_1 - 1)$ 对恒星质量 $M_*$ 选择的晕圈和星系的偏差的描述很差，而由 $b_ 更好地描述\phi(M_*) = 2\delta_c(b_1(M_*) - p)$ 与 $p \in [0.4, 0.7]$。这可以通过物质密度和局部 PNG 对恒星与晕质量关系的中值的不同影响来解释。这种影响的一个简单模型使我们能够很好地描述 $b_1$ 和 $b_\phi$ 的恒星质量依赖性。对于通过颜色和黑洞质量吸积率选择的星系，我们的结果还显示了 $b_1$ 和 $b_\phi$ 之间的重要关系。我们的结果为使用星系聚类的局部 PNG 约束和预测提供了 $b_\phi$ 上的精确先验。鉴于广泛使用的普遍性关系低估了 $b_\phi(M_*)$，