http://arxiv.org/abs/1504.07194

Though megamasers are used to probe extragalactic phenomena, questions remain regarding their production and connection to galactic processes. The observation that water and hydroxyl megamasers rarely coexist in the same galaxy has given rise to the hypothesis that the two megamaser species appear in different phases of nuclear activity or that somehow their presence distinguishes different physical conditions in the medium. However, simultaneous hydroxyl and water megamaser emission has recently been detected in IC 694. Studies of this object are underway but, because many megamasers have not been surveyed for emission in the other molecule, it remains unclear whether IC 694 occupies a narrow phase of galaxy evolution or whether the relationship between megamaser species and galactic processes is more complicated than previously believed. In this paper, we present preliminary results of a systematic search for 22 GHz water maser emission among OH megamaser hosts to identify additional objects hosting both megamaser species to constrain the frequency of the phenomenon. Our work roughly doubles the number of galaxies searched for emission in both molecules which host at least one confirmed maser. We report a definitive ($> 8 \sigma$) detection of water emission toward II Zw 96, firmly establishing it as the second object to co-host both water and hydroxyl megamasers after IC 694. We find high luminosity, narrow features in the water feature in II Zw 96, evidence that at least a part of the maser emission is from an accreting AGN. Additionally, we report evidence for a water megamaser in IRAS 15179+3956. All dual megamaser candidates appear in merging galaxy systems suggestive that megamaser coexistance may signal a brief phase along the merger sequence. Our observations provide possible evidence for an exclusion of H$_2$O kilomasers among OH megamaser hosts.

Read this paper on arXiv…

B. Wiggins, V. Migenes and J. Smidt
Tue, 28 Apr 15
57/70

Comments: 11 pages, 8 figures