Issue |
A&A
Volume 513, April 2010
|
|
---|---|---|
Article Number | A18 | |
Number of page(s) | 6 | |
Section | Extragalactic astronomy | |
DOI | https://doi.org/10.1051/0004-6361/200913864 | |
Published online | 15 April 2010 |
The radio-loud active nucleus in the “dark lens” galaxy J1218+2953
1
FÖMI Satellite Geodetic Observatory, PO Box 585,
1592 Budapest, Hungary e-mail: frey@sgo.fomi.hu
2
MTA Research Group for Physical Geodesy and Geodynamics, PO Box 91,
1521 Budapest, Hungary
3
Joint Institute for VLBI in Europe, Postbus 2,
7990 AA Dwingeloo, The Netherlands e-mail: [zparagi; campbell]@jive.nl
4
MTA Konkoly Observatory, PO Box 67, 1525 Budapest, Hungary e-mail: moor@konkoly.hu
Received:
14
December
2009
Accepted:
22
January
2010
Context. There is a possibility that the optically unidentified radio source J1218+2953 may act as a
gravitational lens, producing an optical arc ~4 away from the
radio position. Until now, the nature of the lensing object has been
uncertain since it is not detected in any waveband other than the radio. The
estimated high mass-to-light ratio could even allow the total mass of this
galaxy to be primarily in the form of dark matter. In this case, J1218+2953 could
be the first known example of a “dark lens”.
Aims. We investigate the nature of J1218+2953 by means of high-resolution radio imaging observations to determine whether there is a radio-loud active galactic nucleus (AGN) in the position of the lensing object.
Methods. We report on Very Long Baseline Interferometry (VLBI) observations with the European VLBI Network (EVN) at 1.6 and 5 GHz.
Results. Our images, having
angular resolutions of ~1 to ~10 milli-arcseconds (mas), reveal a
rich and complex radio structure extending to almost 1. Based on its
radio spectrum and structure, J1218+2953 can be classified as a compact
steep-spectrum (CSS) source, and as a medium-size symmetric object (MSO). The
object harbours an AGN. It is also found as an X-ray source in the XMM-Newton EPIC (European Photon Imaging Cameras) instrument serendipitous source catalogue.
Conclusions. Rather than being a dark lens, J1218+2953 is most likely a massive, heavily obscured galaxy in which the nuclear activity is currently in an early evolutionary stage.
Key words: radio continuum: galaxies / galaxies: active / galaxies: individual: FIRST J121839.7+295325 / techniques: interferometric / gravitational lensing: strong
© ESO, 2010
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