The Hydroxyl-Water Megamaser Connection. I. Water Emission Toward OH
  Megamaser Hosts
  Questions surround the connection of luminous extragalactic masers to
galactic processes. The observation that water and hydroxyl megamasers rarely
coexist in the same galaxy has given rise to a hypothesis that the two species
appear in different phases of nuclear activity. The detection of simultaneous
hydroxyl and water megamaser emission toward IC694 has called this hypothesis
into question but, because many megamasers have not been surveyed for emission
in the other molecule, it remains unclear whether IC694 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 results of a systematic search for 22 GHz water maser emission among
OH megamaser hosts to identify additional objects hosting both megamaser. Our
work roughly doubles the number of galaxies searched for emission in both
molecules which host at least one confirmed maser. We confirm with high degree
of confidence ($> 8 \sigma$) the detection of water emission toward IIZw96,
firmly establishing it as the second object to co-host both water and hydroxyl
megamasers after IC694. We find high luminosity, narrow features in the water
feature in IIZw96. All dual megamaser candidates appear in merging galaxy
systems suggestive that megamaser coexistance may signal a brief phase along
the merger sequence. A statistical analysis of the results of our observations
provide possible evidence for an exclusion of H$_2$O kilomasers among OH
megamaser hosts.
