Radio continuum of galaxies with H₂O megamaser disks: 33 GHz VLA data

Abstract

Context. Galaxies with H 2 O megamaser disks are active galaxies in whose edge-on accretion disks 22 GHz H 2 O 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 H 2 O maser disks and to relate the maser and host galaxy properties to those of the radio continuum emission of the galaxy. Methods. The 33 GHz (9 mm) radio continuum properties of 24 galaxies with reported 22 GHz H 2 O maser emission from their disks are studied in the context of the multiwavelength view of these sources. The 29-37 GHz Ka-band observations are made with the Jansky Very Large Array in B, CnB, or BnA configurations, achieving a resolution of ∼ 0.2 -0.5 arcseconds. Hard X-ray data from the Swift/BAT survey and 22 µm infrared data from WISE, 22 GHz H 2 O maser data and 1.4 GHz 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 33 GHz radio continuum emission at levels of 4.5 -240 σ. 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 (>300 pc) in most sources. Either they do not exist, or our chosen frequency of 33 GHz is too high for a detection of these supposedly steep spectrum features. In only one source among those with known maser disk orientation, NGC 4388, did we find an extended jet-like feature that appears to be oriented perpendicular to the H 2 O megamaser disk. NGC 2273 is another candidate whose radio continuum source might be elongated perpendicular to the maser disk. Smaller 100-300 pc 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 33 GHz luminosity weakly correlates with the infrared luminosity. The 33 GHz luminosity is anticorrelated with the circular velocity of the galaxy. The black hole masses show stronger correlations with H 2 O maser luminosity than with 1.4 GHz, 33 GHz, or hard X-ray luminosities. Furthermore, the inner radii of the disks show stronger correlations with 1.4 GHz, 33 GHz, 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.

Accretion disk versus jet orientation in H2O megamaser galaxies

“…In our pilot project (Kamali et al 2017) we demonstrated a correlation between the disk's inner and outer radii and the 33 GHz radio luminosity of galaxies with H 2 O masers in their nuclear disks (i.e., both inner and outer radii of the disk increase as the radio luminosity increases). In this work, we find a similar correlation for inner and outer disk radius versus the 5 GHz luminosities (Fig.…”

“…Furthermore, the pressure outside the outer disk is less than the critical pressure which permits the existence of the molecules (Neufeld et al 1994) and this critical pressure depends on the X-ray luminosity (for detailed analysis see Neufeld & Maloney 1995). Although a correlation between the X-ray luminosity and the maser disk size is expected, former studies did not find such a correlation (Kamali et al 2017). High energy electrons are responsible for both synchrotron radio emission and the synchrotron self Compton X-ray radiation (Falcke & Biermann 1995).…”

“…Column 2: J2000 right ascension and declination. For NGC 5765b, NGC 6323, NGC 6264 and UGC 9639 the coordinates are taken from NED and for the remaining sources the coordinates are from Kamali et al (2017). Column 3: fringe finders.…”

The Megamaser Cosmology Project. XI. A Geometric Distance to CGCG 074-064

“…In general, the minimum degree of disk-jet misalignment needed to satisfy Equation 9 for a given value of θ will occur when β = 1, so we can impose this value to determine a lower limit on the misalignment. For a typical spectral index of α = 0.7 (Condon et al 1998;Kamali et al 2017), we find that the disk-jet misalignment must be at least ∼7 • ; even for a spectral index as steep as α = 2, the misalignment can be no smaller than ∼5 • . Using a more conservative 3σ upper limit for the unmeasured southern jet component yields misalignment angles of at least ∼5 • and ∼3 • for α = 0.7 and α = 2, respectively.…”

Extragalactic maser surveys

“…Slope, intercept, correlation coefficient and p-values (likelihood that there is no correlation) are also given. From Kamali et al (2017). kinetic temperatures tend to be high, thus providing suitable conditions for the presence of non-metastable ammonia transitions interfereing with the 22 GHz maser emission from H 2 O if there is a continuum which can be absorbed. For an evaluation of the intensity of the NH 3 (3,1) line, then the detection of other non-metastable cm-wave NH 3 inversion transitions will be mandatory.…”