2024A&A...692A.209L

The spectral energy distribution (SED) of low-luminosity active galactic nuclei (LLAGN) presents unique challenges as the emission from these objects is comparable to the radiation from their host galaxy and the accretion physics involved is particularly complex. This study introduces a novel CIGALE module specifically designed to address these challenges. The module combines the empirical L_X-L_12 μm_ relationship with physically motivated accretion models, such as advection-dominated accretion flows (ADAFs) and truncated accretion disks, providing a more accurate depiction of LLAGN central engine emission. A mock analysis of the module revealed good recovery of true parameters, with only a slight bias toward higher input values, further validating its reliability. We tested the module on a sample of 50 X-ray-detected local galaxies, including low-ionization nuclear emission-line regions (LINERs) and Seyferts, and demonstrated its capacity to accurately estimate bolometric luminosities, even in the presence of significant galaxy contamination. Notably, the previous X-ray module failed to provide AGN solutions for this sample, stressing the need for a novel approach. Comparisons with mid-luminosity AGN datasets confirm the module's robustness and applicability up to L_X < 10⁴⁵ erg/s. We also expanded the X-ray-to-bolometric correction formula, making it applicable to AGN spanning ten orders of magnitude in luminosity, and revealing lower k_X values for LLAGN than typically assumed. Additionally, our analysis of the α_ox index, which represents the slope between UV and X-ray emissions, uncovered trends that differ from those observed in high-luminosity AGN. Unlike quasars, where α_ox correlates with λ_Edd, LLAGN exhibit nearly constant or weakly correlated α_ox values, suggesting a shift in accretion physics and photon production mechanisms in low-luminosity regimes. These results underscore the importance of a multiwavelength approach in AGN studies and reveal distinct behaviors in LLAGN compared to quasars. Our findings significantly advance our understanding of LLAGN and offer a comprehensive framework for future research to complete the AGN population census.