Joint Astrophysical Colloquium
Extragalactic water masers at mm/sub-mm wavelengths in the ALMA/NOEMA era
Andrea Tarchi (INAF - Osservatorio Astronomico di Cagliari)
Thursday 24/10/2024 @ 11:30, Sala Antonio Sollima (IV piano Battiferro)
Water masers associated with AGN (the ‘megamasers’) constitute a unique way to directly map the molecular gas at (sub-)parsec distance from supermassive black holes and, hence, to study the physical properties, the structure, and the kinematics of the gas surrounding the central engine. These are key ingredients to build detailed models of AGN and investigate AGN feedback processes. Most previous observational work on water vapor megamasers has focused on the maser transition at a rest frequency of 22 GHz. However, megamaser detections have been obtained in a growing number of galaxies in 183, 321, and 325 GHz water maser transitions. These studies suggest that (sub)millimeter water masers may be common in AGN, associated with nuclear activity like the 22 GHz megamasers sources. In this talk, I will briefly review the main results achieved by 22-GHz megamaser studies. I will then introduce the main mm/sub-mm water (maser) transitions together with a description of the extragalactic objects where they have been found and studied, so far. In the second part of the talk, I will concentrate on a number of recent studies performed by our group in two galaxies, IC485 and TXS2226-184, where extremely luminous nuclear 22-GHz maser emission is present. I will give particular emphasis on the recent ALMA detection in the latter galaxy of maser emission from the water 183 GHz and 380 GHz transitions that, to the best of our knowledge, represents the first case where all three transitions are present in the same object. The potential of the aforementioned studies in view of the existing and upcoming mm/sub-mm facilities is eventually addressed.