Megamasers in Nuclei of Galaxies
Powerful maser emission has been detected in a small number of galaxies. Most of these have Seyfert or starburst nuclei and exhibit other signs of galactic activity. Broad OH emission has been seen in the prototype megamaser IC 4553 (= Arp 220) (Baan, Wood, and Haschick 1982; Baan and Haschick 1984; Norris et al. 1985), NGC 3690 and Mrk 231 (Baan 1985). Powerful H2O emission has been observed in five galaxies (Baan 1985) of which NGC 3079 is the most luminous. Recently formaldehyde emission has been detected in IC 4553 and possibly in NGC 3079 (Baan, Güsten and Haschick 1985). The galaxies with maser emission are usually prominent infrared emitters. Some have perturbed disks with dust lanes and are showing evidence of bursts of star formation; others are part of a strongly interacting system.
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