Investigating the bulge morphology of dual AGN host galaxies from the GOTHIC survey

Abstract

We present a structural analysis of bulges in dual active galactic nuclei (AGNs) host galaxies. Dual AGNs arise in galaxy mergers where both supermassive black holes are actively accreting. The AGNs are typically embedded in compact bulges, which appear as luminous nuclei in optical images. Galaxy mergers can result in bulge growth, often via star formation. The bulges can be discy (pseudo-bulges), classical bulges, or belong to elliptical galaxies. Using Sloan Digital Sky Survey Data Release 18 gri images and GALFIT modelling, we performed 2D decomposition for 131 dual AGNs bulges (comprising 61 galaxy pairs and 3 galaxy triplets) identified in the GOTHIC survey. We derived Sersic ´ indices, luminosities, masses, and scale lengths of the bulges. Most bulges (105/131) are classical, with Sersic ´ indices lying between n = 2 and n = 8. Among these, 64 per cent are elliptical galaxies, while the remainder are classical bulges in disc galaxies. Only ∼20 per cent of the sample exhibits pseudo-bulges. Bulge masses span 1.5 × 109 M to 1.4 × 1012 M, with the most massive systems being ellipticals. Galaxy-type matching shows that elliptical–elliptical and elliptical–disc mergers dominate over disc–disc mergers. At least one galaxy in two-thirds of the dual AGN systems is elliptical and only ∼30 per cent involve two disc galaxies. Although our sample is limited, our results suggest that dual AGNs preferentially occur in evolved, red, quenched systems, which typically form via major mergers. They are predominantly hosted in classical bulges or elliptical galaxies rather than star-forming disc galaxies.