Multiwavelength observations of the triple-peaked AGN Mrk 622

Abstract

ABSTRACT A detailed multiwavelength study of the properties of the triple-peaked active galactic nucleus (AGN) Mrk 622 showing different aspects of the nuclear emission region is presented. Radio, near- and mid-infrared, optical, and X-ray data have been considered for the analysis. In the optical, the WHAN diagnostic diagrams show that the three nuclear peaks are strong active galactic nuclei since the equivalent width of H α is > 6 Å  and log  [N ii] λ6584/H α  ratio is > −0.4. Optical variability of both the continuum flux and intensity of the narrow emission lines is detected in a time span of 13 yr. The size of the narrow-line region is found to be 2.7 pc, with a light-crossing time of 8.7 yr. Analysis done to an archival Hubble Space Telescope image at 1055.2 nm shows that the host galaxy has a 3.6 kpc inner bar with PA  =  74°, faint spiral arms, and a pseudobulge, evolving through secular processes. High-resolution mid-infrared images obtained with the Gran Telescopio Canarias (GTC) and the instrument CanariCam show that the nuclear emission at 11.6 $\rm{\mu m}$ is not spatially resolved. Very Large Array archival observations at 10 GHz reveal a core source with a total flux density of 1.47 ± 0.03 mJy. The spectral index of the core between 8 and 12 GHz is −0.5 ± 0.2, characteristic of AGN. The core deconvolves into a source with dimensions of 82 ± 13 mas $\, \times \,$ 41 ± 20 mas, and a PA = 70  ±  18 deg, which suggests that the core is elongated or that it is constituted by multiple components distributed along a ∼65° axis.