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Fig. 1


Spectra of the four 22 GHz water megamasers detections. Velocities are in the kinematic local standard of rest (LSR) frame and use the optical convention. Recession velocities, Vsys, are adopted from NED. The channel spacing is 0.3 km s-1. The uncertainty of the flux density scale is ≤15%. Top left: maser features towards possible Sy 2 galaxy 2MFGC 13581 are typical of masing sub-parsec accretion disks around AGN. Top right: IRAS 17526+3253 (UGC 11035) is an OH KM galaxy and has narrow 360 L water masers. Bottom left: NGC 4261 (3C 270; twin jet, torus) shows deep H  I absorption at 2260 km s-1 (right inset) and deep 6 GHz OH absorption at 2100–2400 km s-1 (left inset) against the counter-jet (insets adopted from van Langevelde et al. 2000; Impellizzeri 2008). The broad H2O MM feature is slightly redshifted with respect to the systemic velocity. Bottom right: IRAS 20550+1656 (II Zw 96) is an OH MM object and has a tentative H2O MM detection at 5σ after 16-channel Gaussian smoothing (inset). Fits for two main features that are symmetric around Vsys are overlaid, together with two narrower “suggestive” features that are also symmetric but otherwise similar to the noise peaks even after stronger smoothing.

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