2001/10/24 by J. S. Ulvestad, James S. Ulvestad, Luis C. Ho · 6 citations
Physics and Astronomy · #Accretion (finance) #Active galactic nucleus #Astronomy #Astrophysical Phenomena and Observations #Astrophysics #Astrophysics and Cosmic Phenomena #Brightness #Galaxies: Formation, Evolution, Phenomena #Galaxy #Jet (fluid) #Luminosity #Physics #Radiative transfer #Radio galaxy #Schwarzschild radius #Spectral line #astro-ph
paper · pdf · doi:10.1086/338254
To appear in ApJ (Letters). 4 pages
arxiv created 2001/10/24 · openalex publication_date 2002/07/26 · arxiv updated 2009/12/01 · openalex created_date 2025/10/10 · openalex updated_date 2026/08/05
The low-luminosity active galactic nuclei in NGC 3147, NGC 4203, and NGC 4579 have been imaged at four frequencies with the Very Long Baseline Array. The galaxies are unresolved at all frequencies, with size upper limits of 10 3 -10 4 times the Schwarzschild radii of their central massive black holes. The spectral indices between 1.7 and 5.0 GHz range from 0.2 to 0.4; one and possibly two of the galaxies show spectral turnovers between 5.0 and 8.4 GHz. The high brightness temperatures ( T b ≳ 10 9 K) and relatively straight spectra imply that free-free emission and/or absorption cannot account for the slightly inverted spectra. Although the radio properties of the cores superficially resemble predictions for advection-dominated accretion flows, the radio luminosities are too high compared with the X-ray luminosities. We suggest that the bulk of the radio emission is generated by a compact radio jet, which may coexist with a low radiative efficiency accretion flow.