Submillimeter H${}_2$O megamasers in NGC 4945 and the Circinus galaxy

Abstract

We present 321 GHz observations of five AGN from ALMA Cycle 0 archival data: NGC 5793, NGC 1068, NGC 1386, NGC 4945, and the Circinus galaxy. Submillimeter maser emission is detected for the first time towards NGC 4945, and we present a new analysis of the submillimeter maser system in Circinus. None of the other three galaxies show maser emission, though we have detected and imaged the continuum from every galaxy. Both NGC 4945 and Circinus are known to host strong ($\gtrsim 10$ Jy) 22 GHz megamaser emission, and VLBI observations have shown that the masers reside in the innermost $\sim 1$ parsec of the galaxies. The peak flux densities of the 321 GHz masers in both systems are substantially weaker (by a factor of $\sim$100) than what is observed at 22 GHz, though the corresponding isotropic luminosities are more closely matched (within a factor of $\sim$10) between the two transitions. We compare the submillimeter spectra presented here to the known 22 GHz spectra in both galaxies, and we argue that while both transitions originate from the gaseous environment near the AGN, not all sites are necessarily in common. In Circinus, the spectral structure of the 321 GHz masers indicates that they may trace the accretion disk at radii interior to the 22 GHz masers. The continuum emission in NGC 4945 and NGC 5793 shows a spatial distribution indicative of an origin in the galactic disks (likely thermal dust emission), while for the other three galaxies the emission is centrally concentrated and likely originates from the nucleus.

9 pages, 3 figures, accepted for publication in ApJ

References in corpus (3)

• Updated Nearby Galaxy Catalog
• Molecular line emission in NGC1068 imaged with ALMA. I An AGN-driven outflow in the dense molecular gas
• Search for sub-millimeter H2O masers in active galaxies - the detection of a 321 GHz H2O maser in NGC4945

Cited by in corpus (12)

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• TeraHertz Exploration and Zooming-in for Astrophysics (THEZA): ESA Voyage 2050 White Paper
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• Sub-arcsecond imaging of the water emission in Arp 220
• Detection of 36 GHz Class I Methanol Maser Emission Towards NGC 4945
• Search for sub-millimeter H2O masers in active galaxies - the detection of a 321 GHz H2O maser in NGC4945
• 183 GHz water megamasers in active galactic nuclei: a new accretion disk tracer
• Second Epoch ALMA Observations of 321 GHz Water Maser Emission in NGC 4945 and the Circinus Galaxy
• Investigations of the Class I methanol masers in NGC 4945
• ALMA detection of millimetre 183 GHz H2O maser emission in the Superantennae galaxy at z ~ 0.06
• ALMA Detection of 321 GHz water maser emission in the radio galaxy NGC 1052
• Extragalactic maser surveys