http://arxiv.org/abs/2012.04637
Halo occupation distribution (HOD) models describe the number of galaxies that reside in different haloes, and are widely used in galaxy-halo connection studies using the halo model (HM). Here, we introduce and study HOD {\it response functions} $R_\O^g$ that describe the {\it response} of the HODs to long-wavelength perturbations $\O$. The linear galaxy bias parameters $b_\O^g$ are a weighted version of $b_\O^h + R_\O^g$, where $b_\O^h$ is the halo bias, but the contribution from $R_\O^g$ is routinely ignored in the literature. We investigate the impact of this by measuring the $R_\O^g$ in separate universe simulations of the IllustrisTNG model for three types of perturbations: total matter perturbations, $\O = \delta_m$; baryon-CDM compensated isocurvature perturbations, $\O = \sigma$; and potential perturbations with local primordial non-Gaussianity, $\O \propto\fnl\phi$. Our main takeaway message is that the $R_\O^g$ are not negligible in general and their size should be estimated on a case-by-case basis. For stellar-mass selected galaxies, the responses $R_\phi^g$ and $R_\sigma^g$ are sizeable and cannot be neglected in HM calculations of the bias parameters $b_\phi^g$ and $b_\sigma^g$; this is relevant for constraint studies of inflation. On the other hand, we do not detect a strong impact of the HOD response $R_1^g$ on the linear galaxy bias $b_1^g$. These results can be explained by the impact that the perturbations $\O$ have on stellar-to-total-mass relations. We also look into the impact on the bias of the gas distribution and find similar conclusions. We show that a single extra parameter describing the overall amplitude of $R_\O^g$ recovers the measured $b_\O^g$ well, which indicates that $R_\O^g$ can be easily added to HM/HOD studies as a new ingredient.
R. Voivodic and A. Barreira
Wed, 9 Dec 20
21/80
Comments: 22 pages, 12 figures, 1 table. Comments are welcome!
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