The Circinus galaxy: a second case of intense nuclear H2O emission

H2O maser emission has been detected in the Circinus galaxy from within 10-15 arcsec of its nucleus. It consists of several faint broad bands between the heliocentric velocities of 500 and 630 km s-1, on which are superimposed several narrow (of the order of 1 km s-1) features with peak intensities as high as 12Jy. The three brightest narrow-band features have a symmetry in velocity differences which suggests the presence of maser emission from a narrow shell expanding at a velocity of 27.5 km s-1. For a distance of 4 Mpc the luminosity is 37 L suns. This galaxy is the second found to to have nuclear H2O emission with a luminosity at least an order of magnitude greater than any known H2O source in our Galaxy. (author)