2017A&A...605A..84K

Context. Galaxies with H₂O megamaser disks are active galaxies in whose edge-on accretion disks 22GHz H₂O maser emission has been detected. Because their geometry is known, they provide a unique view into the properties of active galactic nuclei.
Aims. The goal of this work is to investigate the nuclear environment of galaxies with H₂O maser disks and to relate the maser and host galaxy properties to those of the radio continuum emission of the galaxy.
Methods. The 33GHz (9mm) radio continuum properties of 24 galaxies with reported 22GHz H₂O maser emission from their disks are studied in the context of the multiwavelength view of these sources. The 29-37GHz Ka-band observations are made with the Karl Jansky Very Large Array in B, CnB, or BnA configurations, achieving a resolution of ∼0.2-0.5-arcsec. Hard X-ray data from the Swift/BAT survey and 22µm infrared data from WISE, 22GHz H₂O maser data and 1.4GHz data from NVSS and FIRST surveys are also included in the analysis.
Results. Eighty-seven percent (21 out of 24) galaxies in our sample show 33GHz radio continuum emission at levels of 4.5-240σ. Five sources show extended emission (deconvolved source size larger than 2.5 times the major axis of the beam), including one source with two main components and one with three main components. The remaining detected 16 sources (and also some of the above-mentioned targets) exhibit compact cores within the sensitivity limits. Little evidence is found for extended jets (>300pc) in most sources. Either they do not exist, or our chosen frequency of 33GHz is too high for a detection of these supposedly steep spectrum features. In NGC 4388, we find an extended jet-like feature that appears to be oriented perpendicular to the H₂O megamaser disk. NGC 2273 is another candidate whose radio continuum source might be elongated perpendicular to the maser disk. Smaller 100-300pc sized jets might also be present, as is suggested by the beam-deconvolved morphology of our sources. Whenever possible, central positions with accuracies of 20-280 mas are provided. A correlation analysis shows that the 33GHz luminosity weakly correlates with the infrared luminosity. The 33GHz luminosity is anticorrelated with the circular velocity of the galaxy. The black hole masses show stronger correlations with H₂O maser luminosity than with 1.4GHz, 33GHz, or hard X-ray luminosities. Furthermore, the inner radii of the disks show stronger correlations with 1.4GHz, 33GHz, and hard X-ray luminosities than their outer radii, suggesting that the outer radii may be affected by disk warping, star formation, or peculiar density distributions.