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

Abstract

Understanding the relative roles of large-scale environment and internal host-galaxy processes in shaping AGN activity is essential for constraining models of black-hole growth and galaxy evolution. We investigate how the environment of X-ray selected active galactic nuclei (AGN) relates to black-hole growth and accretion properties, and whether these introduce an environmental dependence beyond that expected from the host galaxy itself. Combining the XXL and Stripe 82X surveys, we construct samples of 427 broad-line AGN at $0.5<z<1.2$ and more than $20,000$ galaxies, with host-galaxy properties derived consistently using the same spectral energy distribution fitting methodology. Dark matter halo (DMH) masses are inferred from AGN--galaxy cross-correlation functions, while a multivariate nearest-neighbour matching algorithm is used to isolate trends with black-hole mass ($M_{\mathrm{BH}}$), Eddington ratio ($λ_{\mathrm{Edd}}$), and X-ray luminosity ($L_{\mathrm{X}}$) under controlled host-galaxy conditions. Within the uncertainties of the present dataset, X-ray AGN typically reside in halos of $\log(M_{\mathrm{DMH}}/h^{-1}M_\odot)\simeq13$, with no significant variation as a function of $M_{\mathrm{BH}}$, $λ_{\mathrm{Edd}}$, or $L_{\mathrm{X}}$. These results suggest that neither long-term black-hole growth nor short-term accretion variability is strongly linked to large-scale environment, and instead support a scenario in which AGN properties are regulated primarily by internal host-galaxy processes, while large-scale structure sets the broader boundary conditions for gas supply and duty cycle.

Figures (8)

• Figure 1: Distributions of the sSFR ($\mathrm{sSFR} = \mathrm{SFR}/M_\star$), for galaxies (top panel) and X-ray AGN (bottom panel) for the two fields, as indicated in the legend.
• Figure 2: Distribution of key physical properties for the combined X-ray AGN sample from the XXL and Stripe 82X surveys. From left to right and top to bottom, the panels show the distributions of black-hole mass ($\log M_{\mathrm{BH}}/M_\odot$), Eddington ratio ($\log \lambda_{\mathrm{Edd}}$), X-ray luminosity ($\log L_{\mathrm{X}}/\mathrm{erg\,s^{-1}}$), stellar mass ($\log M_\star/M_\odot$), star-formation rate ($\log \mathrm{SFR}/M_\odot\,\mathrm{yr^{-1}}$), and specific star-formation rate ($\log \mathrm{sSFR}/\mathrm{Gyr^{-1}}$). All quantities are shown in logarithmic units.
• Figure 3: Correlation function measurements: Top panel: AGN–galaxy cross-correlation function (black points) and galaxy autocorrelation function (orange points) for the combined XXL and Stripe 82X samples, shown together with their best-fitting models (solid lines). Middle and bottom panels: same measurements performed separately for each field, compared with the combined results. The corresponding DMH mass estimates for each field and for the merged dataset are listed in Table \ref{['table_total']}. Data points have been offset in the x-axis for clarity.
• Figure 4: AGN--galaxy cross-correlation functions as a function of $M_{\mathrm{BH}}$, in two L$_X$ bins, as indicated in the legend. The corresponding DMH mass estimates are listed in Table \ref{['table_mbh']}.
• Figure 5: AGN--galaxy cross-correlation functions as a function of $\lambda_{\mathrm{Edd}}$, in two L$_X$ bins, as indicated in the legend. The corresponding DMH mass estimates are listed in Table \ref{['table_nedd']}.