Large-scale environments of star-forming active galactic nuclei: How black-hole mass, accretion rate, and luminosity connect to dark-matter halos

¹ Instituto de Fisica de Cantabria (CSIC-Universidad de Cantabria), Avenida de los Castros, 39005 Santander, Spain
² Department of Physics and Astronomy, University of Southampton, Highfield, Southampton SO17 1BJ, UK
³ Institute for Astronomy & Astrophysics, National Observatory of Athens, V. Paulou & I. Metaxa, Athens 11532, Greece

^★ Corresponding author: This email address is being protected from spambots. You need JavaScript enabled to view it.

Received: 2 February 2026
Accepted: 10 March 2026

Abstract

Understanding the relative roles of large-scale environment and internal host-galaxy processes in shaping active galactic nuclei (AGN) activity is key to constraining models of black-hole growth and galaxy evolution. In this work, we investigated how the environment of X-ray-selected active galactic nuclei (AGNs) relates to black-hole growth and accretion properties, and whether these introduce a dependence on a large-scale environment beyond that set by the host galaxy itself. By combining the XXL and Stripe 82X surveys, we assembled samples of 427 broad-line AGNs at 0.5 < z < 1.2 and over 20 000 galaxies, with host-galaxy properties consistently derived using the same spectral energy distribution fitting methodology and assumptions. Dark-matter halo (DMH) masses were inferred from AGN–galaxy cross-correlation functions, while a multivariate nearest-neighbour matching algorithm was applied to isolate trends with black-hole mass (M_BH), Eddington ratio (λ_Edd), and X-ray luminosity (L_X) under controlled host-galaxy conditions. Within the statistical uncertainties of the present dataset, we find that X-ray AGNs typically reside in halos of log(M_DMH/h⁻¹ M_⊙)≃13, with no significant variation as a function of M_BH, λ_Edd, or L_X. Neither M_BH nor λ_Edd shows a measurable correlation with large-scale environment, which is consistent with a scenario in which long-term black-hole growth and short-term accretion variability are primarily regulated by internal host-galaxy processes rather than halo-scale mass alone. The absence of a statistically significant M_DMH–L_X trend further indicates that AGN radiative output reflects stochastic or feedback-regulated variability, rather than direct modulation by the large-scale environment. Overall, these results support a self-regulated co-evolution framework in which large-scale structure sets the boundary conditions for gas availability and AGN duty cycle, while the subsequent growth and luminosity evolution of AGNs are determined predominantly by local processes within their host galaxies.