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Date and Time of the Query: 2019-06-26 T17:28:04 PDT
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For refcode 2009ApJ...706L.260G:
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Copyright by American Astronomical Society. Reproduced by permission
2009ApJ...706L.260G The Faintest Seyfert Radio Cores Revealed by VLBI Giroletti, Marcello; Panessa, Francesca 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 10^19^ 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 {mu}Jy. The detected compact nuclei have rather different radio properties: spectral indices range from steep ({alpha}>0.7) to slightly inverted ({alpha} = --0.1), brightness temperatures vary from T_B_ = 10^5^ K to larger than 10^7^ 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. Key words: galaxies: active, galaxies: Seyfert, radio continuum: galaxies
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