Second Epoch ALMA Observations of 321 GHz Water Maser Emission in NGC 4945 and the Circinus Galaxy

Abstract

We present the results of second epoch ALMA observations of 321 GHz H${}_2$O emission toward two nearby active galactic nuclei, NGC 4945 and the Circinus galaxy, together with Tidbinbilla 70-m monitoring of their 22 GHz H${}_2$O masers. The two epoch ALMA observations show that the strengths of the 321 GHz emission are variable by a factor of at least a few, confirming a maser origin. In the second epoch, 321 GHz maser emission from NGC 4945 was not detected, while for the Circinus galaxy the flux density significantly increased and the velocity gradient and dispersion have been measured. With the velocity gradient spanning $\sim$110 km/s, we calculate the disk radius to be $\sim$28 pc, assuming disk rotation around the nucleus. We also estimate the dynamical mass within the central 28 pc to be 4.3 $\times$ 10${}^8$ M${}_{\odot }$, which is significantly larger than the larger scale dynamical mass, suggesting the velocity gradient does not trace circular motions on that scale. The overall direction of the velocity gradient and velocity range of the blueshifted features are largely consistent with those of the 22 GHz maser emission in a thin disk with smaller radii of 0.1--0.4 pc and molecular outflows within $\sim$1 pc from the central engine of the galaxy, implying that the 321 GHz masers could trace part of the circumnuclear disk or the nuclear outflows.

13 pages, 9 figures, accepted for publication in ApJ

References in corpus (9)

• The 2-79 keV X-ray Spectrum of the Circinus Galaxy with NuSTAR, XMM-Newton and Chandra: a Fully Compton-Thick AGN
• The variable hard X-ray emission of NGC4945 as observed by NuSTAR
• ALMA 0.02"-resolution observations reveal HCN-abundance-enhanced counter-rotating and outflowing dense molecular gas at the NGC 1068 nucleus
• Spatially resolved Fe K spectroscopy of NGC 4945
• The Molecular Gas in the NGC 6240 Merging Galaxy System at the Highest Spatial Resolution
• The Large-Scale Atomic and Molecular Gas in the Circinus Galaxy
• Submillimeter Array Observations of 321 GHz Water Maser Emission in Cepheus A
• Detection of 183 GHz water megamaser emission towards NGC 4945
• ALMA detection of millimetre 183 GHz H2O maser emission in the Superantennae galaxy at z ~ 0.06

Cited by in corpus (5)

• Key Science Goals for the Next-Generation Event Horizon Telescope
• 183 GHz water megamasers in active galactic nuclei: a new accretion disk tracer
• ALMA Detection of 321 GHz water maser emission in the radio galaxy NGC 1052
• Non-detection of Broad Hydrogen Radio Recombination Lines in Circinus Galaxy
• X-ray and CO-Derived Column Densities in AGN: A Study of Obscuration Properties in CTAGN and Non-CTAGN