Peculiar galaxy IC 4553: VLA-A observations of the OH megamaser

The OH emission of the peculiar galaxy IC 4553 has been studied using the VLA-A. Two sets of observations are discussed in this work, the first one with a low-velocity resolution covering all the OH emission features of IC 4553 and a second one with a high-velocity resolution covering the 1667 MHz line. The galaxy has two different emisssion regions, which are both superposed on the radio continuum source. The regions each produce the 1667 and 1665 MHz OH emission features, but the weaker second region is redshifted by roughly 300 km s-1 relative to the stronger main region. The emission from the main region reveals velocity structure which is consistent with solid body rotation of a molecular disk. The second emission region is most likely due to molecular clouds falling into the radio nucleus. The phenomena in IC 4553 are interpreted in terms of the galaxy merger taking place in the object. The H I absorption and possible OH absorption likely originate in the foreground galaxy, while the radio source and the main OH emission is in the background galaxy. The maser emission is interpreted as low-gain unsaturated maser amplification of the radio continuum by intervening molecular material. The population inversion required for the OH is acceptable considering the activity within the nucleus of the galaxy