Cross-correlation of Luminous Red Galaxies with ML-selected AGN in HSC-SSP III: HOD Parameters for Type I and Type II Quasars

Rodrigo Córdova Rosado, Andy D. Goulding, Jenny E. Greene, Nickolas Kokron, Andrina Nicola, Michael A. Strauss, Ryan C. Hickox

First listed 2025-10-13 | Last updated 2025-10-13

Abstract

Understanding the dark matter (DM) halo environment in which galaxies that host active galactic nuclei (AGN) reside is a window into the nature of supermassive black hole (SMBH) accretion. We apply halo occupation distribution (HOD) modeling tools to interpret the angular cross-correlation functions between $1.5\times10^6$ luminous red galaxies (LRGs) and our $\sim28,500$ Hyper Suprime-Cam + Wide-field Infrared Survey Explorer-selected (and $L_{6 μm}$-limited) AGN to infer the halo properties of distinct quasar samples at physical scales $s>0.1\,{\rm Mpc}$, for $z\in0.7-1.0$. We find that Type I (unobscured) and Type II (obscured) AGN cluster differently, both on small and large physical scales. The derived HODs imply that Type I AGN reside, on average, in substantially ($\sim3\times$) more massive halos ($M_h \sim 10^{13.4} M_\odot$) than Type II AGN ($M_h \sim 10^{12.9} M_\odot$) at $>5σ$ significance. While Type II AGN show one-halo correlations similar to that of galaxies of their average halo mass, the Type I AGN intra-halo clustering signal is significantly shallower. We interpret this observation with HOD methods and find Type I AGN are significantly less likely ($f_{sat}\sim0.05^{+1}_{-0.05}\%$) to be found in satellite galaxies than Type II AGN. We find reddened + obscured AGN to have typical satellite fractions for their inferred average halo mass ($\sim10^{13} M_\odot$), with $f_{sat} \sim 20^{+10}_{-5}\%$. Taken together, these results pose a significant challenge to the strict unified AGN morphological model, and instead suggest that a quasar's spectral class is strongly correlated with its host galaxy's dark matter halo environment. These intriguing results have provided a more complex picture of the SMBH -- DM halo connection, and motivate future analyses of the intrinsic galaxy and accretion properties of AGN.

Short digest

Using HOD modeling of angular cross-correlations, the authors link ~1.5×10^6 HSC luminous red galaxies with ~28,500 HSC+WISE ML-selected, L6um-limited AGN at z=0.7–1.0 on scales s>0.1 Mpc. They find unobscured (Type I) quasars inhabit ≈3× more massive halos than obscured (Type II)—M_h≈10^13.4 Msun vs 10^12.9 Msun—at >5σ significance. The one-halo term for Type I is markedly shallower, implying an extremely low satellite fraction (f_sat≈0.05%), while reddened+obscured AGN have typical f_sat≈20% for ~10^13 Msun halos. These results argue against a strict orientation-only unified model, tying spectral class to DM halo environment.

Key figures to inspect

• Figure 1: Sensitivity of the projected w(θ) to the 3-parameter HOD—use this to see how each parameter tilts the one-halo vs two-halo balance and to note the minimum fitting scale adopted.
• Figure 2: LRG autocorrelation across the three HSC fields—inspect the jackknife errors and the systematic large-scale residuals that motivate the chosen HOD flexibility and fitting range.
• Figure 3: MCMC posteriors for the LRG 3-parameter HOD—check parameter covariances and the tracer HOD values that anchor the AGN cross-correlation inference.
• Figure 4: LRG×AGN cross-correlation with 3- vs 5-parameter HOD fits—compare residuals and small-scale slopes that drive the satellite fraction constraints and the Type I shallow one-halo signal.