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Title:
The Faintest Seyfert Radio Cores Revealed by VLBI
Authors:
Giroletti, Marcello; Panessa, Francesca
Affiliation:
AA(INAF Istituto di Radioastronomia, via Gobetti 101, 40129 Bologna, Italy ), AB(IASF/INAF, via del Fosso del Cavaliere 100, 00133 Roma, Italy )
Publication:
The Astrophysical Journal Letters, Volume 706, Issue 2, pp. L260-L264 (2009). (ApJL Homepage)
Publication Date:
12/2009
Origin:
IOP
ApJ Keywords:
galaxies: active, galaxies: Seyfert, radio continuum: galaxies
DOI:
10.1088/0004-637X/706/2/L260
Bibliographic Code:
2009ApJ...706L.260G

Abstract

In 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.
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