IC 4553 : masers around an active galactic nucleus.

Observations of the OH maser emission of the peculiar galaxy IC4553 obtained with MERLIN at 1.6371 GHz (corresponding to the OH center frequency 1.6664 GHz redshifted by 5400 km/s), and of the continuum emission at 1.665 GHz, are reported and compared with the optical and IR data of Norris (1984). Maps and spectra are shown, and the three spatial components of the core-dominated structure seen in the continuum are found to have intensity peaks at different frequencies in the integrated OH maser emission, suggesting that the continuum image is amplified by an intervening OH-maser cloud with a 50 km/s arcsec cross-cloud velocity gradient. This explanation is consistent with the optical and IR observations, which indicate that IC4553 is an edge-on Seyfert-like galaxy, the OH maser radiation being stimulated by the strong FIR nuclear emission.