Bibcode
Orienti, M.; Prieto, M. A.
Referencia bibliográfica
Monthly Notices of the Royal Astronomical Society, Volume 401, Issue 4, pp. 2599-2610.
Advertised on:
2
2010
Número de citas
74
Número de citas referidas
69
Descripción
We present archival high-spatial-resolution VLA and VLBA data of the
nuclei of seven of the nearest and brightest Seyfert galaxies in the
Southern Hemisphere. At VLA resolution (~0.1arcsec), the nuclei of the
Seyfert galaxies are unresolved, with the exception of MCG-5-23-16 and
NGC7469, which show a core-jet structure. Three Seyfert nuclei are
surrounded by diffuse radio emission related to star-forming regions.
VLBA observations with parsec-scale resolution demonstrate that in
MRK1239 the nucleus is clearly resolved into two components separated by
~30 pc, whereas the nucleus of NGC3783 is unresolved. Further comparison
between VLA and VLBA data of these two sources shows that the flux
density at parsec scales is only 20 per cent of that measured by the
VLA. This suggests that the radio emission is not concentrated in a
single central component, as in elliptical radio galaxies, and an
additional low-surface-brightness component must be present. A
comparison of Seyfert nuclei with different radio spectra shows that the
`presence' of undetected flux on a milliarcsecond scale is common in
steep-spectrum objects, whereas in flat-spectrum objects essentially all
the radio emission is recovered. In the steep-spectrum objects, this
`missing' flux probably results from non-thermal radiation related to
active galactic nuclei, perhaps from a jet that is disrupted in Seyfert
galaxies because of the denser environment of their spiral hosts.
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Centros de Galaxias a Escalas de Parsecs y Técnicas de Alta Resolución Espacial
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