Discovery of Methanimine Megamasers Toward Compact Obscured Galaxy
  Nuclei
  We present the first search for the 5.29 GHz methanimine($\rm{CH}_2\rm{NH}$)
$1_{10}-1_{11}$ transition toward a sample of galaxy nuclei. We target seven
galaxies that host Compact Obscured Nuclei (CONs) with the Karl G. Jansky Very
Large Array. These galaxies are characterized by Compton-thick cores.
$\rm{CH}_2\rm{NH}$ emission is detected toward six CONs. The brightness
temperatures measured toward Arp220 indicate maser emission. Isotropic
luminosities of the $\rm{CH}_2\rm{NH}$ transition, from all sources where it is
detected, exceed 1 L$_{\odot}$ and thus may be considered megamasers. We also
detect formaldehyde ($\rm{H}_2\rm{CO}$) emission toward three CONs. The
isotropic $\rm{CH}_2\rm{NH}$ luminosities are weakly correlated with the
infrared luminosity of the host galaxy and strongly correlated with OH
megamaser luminosities from the same galaxies. Non-LTE radiative transfer
models suggest that the maser is pumped by the intense mm/submm radiation field
of the CONs. Our study suggests that $\rm{CH}_2\rm{NH}$ megamasers are linked
to the nuclear processes within 100 pc of the Compton Thick nucleus within
CONs.
