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VLBA Identification of the Milliarcsecond Active Nucleus in the Seyfert Galaxy NGC 4151 | | James S. Ulvestad
; Diane S. Wong
; Gregory B. Taylor
; Jack F. Gallimore
; Carole G. Mundell
; | | Date: |
7 May 2005 | | Subject: | astro-ph | | Affiliation: | NRAO), Diane S. Wong (University of California), Gregory B. Taylor (NRAO), Jack F. Gallimore (Bucknell University), and Carole G. Mundell (Liverpool John Moores University | | Abstract: | The Seyfert galaxy NGC 4151 has been imaged at resolution better than 0.1 pc using a VLBI array consisting of the VLBA and three 100m-class telescopes. A flat-spectrum 3-mJy source with a monochromatic radio power of ~10^{37} ergs/s has been detected, apparently at the location of the active galactic nucleus (AGN) and its central black hole. The radio source has a minimum brightness temperature of 2.1 x 10^8 K and a size upper limit of 0.035 pc, about 10 times the diameter of the broad-line region and 15,000 times the diameter of the black hole’s event horizon. An additional flat-spectrum component located within a parsec of the apparent nucleus is likely to be a knot in the inner radio jet. The presence of some steep-spectrum radio emission within 0.1 pc of the galaxy nucleus limits the emission measure of a possible ionized torus to a maximum value of 10^8 cm^{-6}pc. If the hard X-ray source in NGC 4151 is associated with the radio AGN, its radio to X-ray ratio is less than 10^{-5}, putting NGC 4151 securely in the radio-quiet class of AGNs. The radio image reveals a 0.2 pc two-sided base to the well-known arcsecond radio jet. Apparent speeds of jet components relative to the radio AGN are <0.050c and <0.028c at respective nuclear distances of 0.16 pc and 6.8 pc. These are the lowest speed limits yet found for a Seyfert galaxy, and indicate non-relativistic jet motions, possibly due to thermal plasma, on a scale only an order of magnitude larger than the broad-line region. | | Source: | arXiv, astro-ph/0505141 | | Services: | Forum | Review | PDF | Favorites | |
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