Astronomy and Astrophysics, volume 417, 925-944 (2004/4-3)
Motion and properties of nuclear radio components in Seyfert galaxies seen with VLBI.
MIDDELBERG E., ROY A.L., NAGAR N.M., KRICHBAUM T.P., NORRIS R.P., WILSON A.S., FALCKE H., COLBERT E.J.M., WITZEL A. and FRICKE K.J.
Abstract (from CDS):
We report EVN, MERLIN and VLBA observations at 18cm, 6cm and 3.6cm of the Seyfert galaxies NGC 7674
, NGC 5506
, NGC 2110
and Mrk 1210
to study their structure and proper motions on pc scales and to add some constraints on the many possible causes of the radio-quietness of Seyferts. The component configurations in NGC 7674
and NGC 2110
are simple, linear structures, whereas the configurations in NGC 5506
and Mrk 1210
have multiple components with no clear axis of symmetry. We suggest that NGC 7674
is a low-luminosity compact symmetric object. Comparing the images at different epochs, we find a proper motion in NGC 7674
of (0.92±0.07)c between the two central components separated by 282pc and, in NGC 5506
, we find a 3 σ upper limit of 0.50c for the components separated by 3.8pc. Our results confirm and extend earlier work showing that the outward motion of radio components in Seyfert galaxies is non-relativistic on pc scales. We briefly discuss whether this non-relativistic motion is intrinsic to the jet-formation process or results from deceleration of an initially relativistic jet by interaction with the pc or sub-pc scale interstellar medium. We combined our sample with a list compiled from the literature of VLBI observations made of Seyfert galaxies, and found that most Seyfert nuclei have at least one flat-spectrum component on the VLBI scale, which was not seen in the spectral indices measured at arcsec resolution. We found also that the bimodal alignment of pc and kpc radio structures displayed by radio galaxies and quasars is not displayed by this sample of Seyferts, which shows a uniform distribution of misalignment between 0° and 90°. The frequent misalignment could result from jet precession or from deflection of the jet by interaction with gas in the interstellar medium.
galaxies: seyfert - galaxies: active - galaxies: jets
Status at CDS:
Tables 2, 4: <[MRN2004] NGC 7674 WW> (Nos SE, NW), <[MRN2004] Mrk 463E A> (Nos L, R), <[MRN2004] Mrk 463E N> (Nos 1-3), <[MRN2004] Mrk 1210 WWN> (Nos NW, SE, NW1-NW4), <[MRN2004] NGC 2110 W> (Nos C, N, S), <[MRN2004] NGC 5506 AN> (Nos B0-B2), <[MRN2004] NGC 7469 N> (Nos 2, 3, 5).
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