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Astron. Astrophys. 335, 463-466 (1998)


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H2O megamaser emission from FR I radio galaxies

C. Henkel 1, 2, Y.P. Wang 1, 3, H. Falcke 1, 4, A.S. Wilson 4, 5 and J.A. Braatz 6

1 Max-Planck-Institut für Radioastronomie, Auf dem Hügel 69, D-53121 Bonn, Germany
2 European Southern Observatory, Casilla 19001, Santiago 19, Chile
3 Purple Mountain Observatory, Academia Sinica, Nanjing 210008, P.R. China
4 Department of Astronomy, University of Maryland, College Park, MD 20742, USA
5 Space Telescope Science Institute, 3700 San Martin Drive, Baltimore, MD 21218, USA
6 Harvard-Smithsonian Center for Astrophysics, 60 Garden St., Cambridge, MA 21218, USA

Received 12 January 1998 / Accepted 30 March 1998

Abstract

A systematic search for 22 GHz [FORMULA] megamaser emission is reported for 50 nearby (z [FORMULA] 0.15) FR I galaxies. No detection was obtained, implying that ultraluminous [FORMULA] masers ([FORMULA] [FORMULA] 103 [FORMULA]) must be rare in early-type galaxies with FR I radio morphology. Despite higher radio core luminosities the detection rate for our sample is lower than in similar surveys of late-type Seyfert galaxies. This puzzling difference between Seyferts and low-power radio galaxies could be explained in several ways: a) the maser emission is saturated and therefore independent of the radio core luminosity, b) the masers are unsaturated and originate in a thin circumnuclear gas disk, so the `seed' radio continuum would come from the far jet which is relativistically dimmed or c) the amount, kinematics, or the distribution of the molecular gas in the nuclei of Seyferts and radio galaxies is different. Further studies of maser properties may provide clues to the differences between radio-loud and radio-quiet AGN.

Key words: Masers – ISM: molecules – galaxies: elliptical and lenticular – galaxies: ISM – galaxies: active – radio lines: galaxies

Send offprint requests to: C. Henkel, MPIfR, Auf dem Hügel 69, D-53121 Bonn, Germany (p220hen@mpifr-bonn.mpg.de)

© European Southern Observatory (ESO) 1998

Online publication: June 18, 1998

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