Marcello Giroletti and Francesca Panessa 2009 ApJ 706 L260 doi:10.1088/0004-637X/706/2/L260
Marcello Giroletti1 and Francesca Panessa2
Show affiliationsIn this Letter, we report on dual-frequency European VLBI Network observations of the faintest and least luminous radio cores in Seyfert nuclei, going to sub-millijansky flux densities and radio luminosities around 1019 W Hz–1. We detect radio emission from the nuclear region of four galaxies (NGC 4051, NGC 4388, NGC 4501, and NGC 5033), while one (NGC 5273) is undetected at the level of ~100 μJy. The detected compact nuclei have rather different radio properties: spectral indices range from steep (α>0.7) to slightly inverted (α = –0.1), brightness temperatures vary from TB = 105 K to larger than 107 K, and cores are either extended or unresolved, in one case accompanied by lobe-like features (NGC 4051). In this sense, diverse underlying physical mechanisms can be at work in these objects: jet-base or outflow solutions are the most natural explanations in several cases; in the case of the undetected NGC 5273 nucleus, the presence of an advection-dominated accretion flow is consistent with the radio luminosity upper limit.
galaxies: active; galaxies: Seyfert; radio continuum: galaxies
98.62.Nx Jets and bursts; galactic winds and fountains
98.62.Qz Magnitudes and colors; luminosities
Issue 2 (2009 December 1)
Received 2009 October 9, accepted for publication 2009 October 29
Published 2009 November 12
Marcello Giroletti and Francesca Panessa 2009 ApJ 706 L260
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