The Water Masers in the Elliptical Galaxy NGC 1052

Very luminous water masers have been detected toward only two elliptical galaxies; the emission lines are relatively broad (≈ 90 km s−1) and smooth, unlike the narrow maser spikes seen in other active galaxies. We have made the first VLBI observations of the water masers in one of these galaxies, NGC 1052. We find that the masers lie along, rather than perpendicular to, the jet. The scale of the maser emission is about 400 μas (7000 AU). The masers could be associated with the radio jet, and we show that the jet is energetically capable of powering the observed maser emission by driving slow, nondissociative shocks into circumnuclear, dense molecular clouds. Alternatively, the masers could represent the amplification of the radio continuum emission of the jet by foreground molecular clouds. Further VLBI observations should be able to distinguish between these two possibilities.