An embedded circumnuclear disk in Mrk 273

Free access article

Issue		A&A Volume 419, Number 3, June I 2004


Page(s)		887 - 896
Section		Extragalactic astronomy
DOI		http://dx.doi.org/10.1051/0004-6361:20040998

A&A 419, 887-896 (2004)
DOI: 10.1051/0004-6361:20040998

An embedded circumnuclear disk in Mrk 273

H.-R. Klöckner^{1, 2} and W. A. Baan²

¹ Kapteyn Institute, University of Groningen, PO Box 800, 9700 AV Groningen, The Netherlands
² ASTRON, Westerbork Observatory, PO Box 2, 7990 AA Dwingeloo, The Netherlands

(Received 8 January 2004 / Accepted 13 February 2004 )

Abstract
Radio observations using very long baseline interferometry (VLBI) and the Westerbork interferometer have been carried out to study the hydroxyl Megamaser emission in Mrk 273 at different spatial resolutions. Line and continuum observations were carried out by the European VLBI network (EVN) at 1.6 GHz and display a number of distinct structural components in the central arcsec ² region. The observed continuum emission shows three prominent regions with both flat and steep spectral indexes. The hydroxyl (OH) emission detected by the EVN measurements accounts for only 12 percent of the total OH emission in Mrk 273, but it does show the same dominant 1667 MHz line emission components as the WSRT observations. The spatial distribution of the maser emission provides a high resolution view of the molecular environment in the nuclear region. The OH emission has only been detected toward a distinct radio source in the northern nucleus with a spatial extent of 108 pc. The OH emission is only partially superposed on the radio continuum and is associated with the near-infrared emission source. The low pump efficiency of the maser and the OH main-line ratio suggest that this emission originates in an optically thin and unsaturated maser environment with a complex pumping scheme that cannot be explained by radiative infrared pumping with a single dust temperature. The specific line emission pattern and the line-of-sight velocities indicate the organized structure of an edge-on disk/TORUS with a Keplerian rotation surrounding a central object with a binding mass of 1.39 $\pm$ 0.16 $\times$ 10⁹ M $_{\normalsize\odot}$ .

Key words: galaxies: individual: Mrk 273 -- masers -- galaxies: ISM -- galaxies: kinematics and dynamics

Offprint request: H.-R. Klöckner, hrkloeck@astro.rug.nl

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