## Water maser in a radio-loud galaxy (3C403)

We report the first detection of a water megamaser in a radio-loud galaxy, 3C 403, and present a follow-up study using the VLA. 3C 403 has been observed as a part of a small sample of FR II galaxies with evidence of nuclear obscuration. The isotropic luminosity of the maser is ~ 1200 L_o. With a recessional velocity of cz ~ 17680 km s-1 it is the most distant water maser so far reported. The line arises from the densest (> 10^8 cm^-3) interstellar gas component ever observed in a radio-loud galaxy. Two spectral features are identified, likely bracketing the systemic velocity of th e galaxy. Our interferometric data clearly indicate that these arise from a location within 0.1" (~ 110 pc) from the active galactic nucleus. We conclude that the maser spots are most likely associated with the tangentially seen parts of a nuclear accretion disk, while an association with dense warm gas interacting with the radio jets cannot yet be ruled out entirely.

Published in:

Tarchi A., Brunthaler A., Henkel C., Menten K.M., Braatz J., Weiss A., 2007, A&A 475, 497

Maser lines in 3C 403 with a channel spacing of 78 kHz or 1.15 km s-1 ( upper panel) and 1.25 MHz or 17.8 km s-1 ( lower panel). The arrow marks the systemic velocity of the galaxy, $V_{\rm sys}$ = cz = 17 688 km s-1.