The disk plus (failed) wind system of 3C 47: A story of accretion disks and binary black holes

Optically thick, geometrically thin accretion disks around supermassive black holes are thought to contribute to broad-line emission in type-1 active galactic nuclei (AGN). However, observed emission line profiles most often deviate from those expected from a rotating disk, and the role of accretion disks in contributing to broad Balmer lines and high-ionization UV lines such as CIV λ 1549 in radio-loud (relativistically “jetted”) AGN remains unclear. This report builds on the findings of three previous studies and places them within a broader context, offering new insights and a more coherent interpretation of earlier results and their implications. It examines the role of accretion disks in broad-line emission, with particular emphasis on radio-loud quasars. We applied a quantitative parametrization of the low-ionization broad emission line properties in the main sequence context. We stressed that broad emission lines show large red-ward asymmetry both in H β and Mg II λ 2800. An unbiased comparison matching black hole mass and Eddington ratio suggests that the most powerful RL quasars show the highest red-ward asymmetries in H β in the general population of AGN. These shifts can be accounted for by gravitational and transverse redshift effects, especially for black hole masses larger than ≈ 10 8.7 M ⊙ . The analysis of the extremely jetted quasar 3C 47 added another piece to the puzzle: not only are the low ionization profiles of 3C 47 well-described by a relativistic Keplerian accretion disk model, with line emission between ≈ 100 and ≈ 1,000 gravitational radii, but also the high-ionization line profiles can be understood as a combination of disk plus a failed wind contribution that is in turn hiding the disk emission. Constraints on radio properties and line profile variability suggest that 3C 47 might involve the presence of a second black hole with secondary-to-primary mass ratio ≲ 0.5 . We conjecture that the double peakers — type-1 AGN with Balmer line profiles consistent with accretion disk emission — might have their emission truncated by the sweeping effect of a second black hole. Our analysis of 3C 47 provides original evidence that the ubiquitous red asymmetry in Population B is consistent with gravitational and transverse redshift from the accretion disk. In non-starving systems, the disk signal is plausibly masked by additional line emission, rendering the disk contribution harder to detect.