The megamaser galaxy Markarian 273. II - VLA observations of the neutral hydrogen absorption

The high-resolution A-array of the VLA was used to observe the wide neutral hydrogen absorption in the OH megamaser galaxy Mrk 273. The nuclear continuum of this galaxy is extended at 21 cm; Ulvestadt and Wilson (1984) find a double structure at 6 cm where the stronger component is resolved into a triple at 2 cm. The H I absorption is marginally resolved both spatially and spectrally and different features can be identified. These features are distinguishable as basically Gaussian components of the absorption but are probably not independent; several of these may form a rotating disk with a velocity gradient of 1.89 km/s per parsec. Assuming a typical rotational velocity of about 200 km/s, the radius of this disk would be R = 106 pc and the total internal mass can be estimated at M = 10 to the 9th solar masses. These parameters, when compared with the same values of other extragalactic H I absorption disks, are not highly unusual and are, possibly, quite believable.