期刊
PUBLICATIONS OF THE ASTRONOMICAL SOCIETY OF JAPAN
卷 53, 期 2, 页码 169-178出版社
OXFORD UNIV PRESS
DOI: 10.1093/pasj/53.2.169
关键词
galaxies : active; galaxies : individual (NGC 1052; 0238-084); galaxies : nuclei; radio continuum : galaxies; techniques : interferometric
A subparsec-scale dense plasma torus around an active galactic nucleus is unveiled. We report on very-long baseline interferometry (VLBI) observations at 2.3, 8.4, and 15.4 GHz towards the active galaxy NGC 1052. The convex spectra of the double-sided jets and the nucleus imply that synchrotron emission is obscured through free-free absorption (FFA) by the foreground cold dense plasma. A trichromatic image was produced to illustrate the distribution of the FFA opacity. We found a central condensation of the plasma which covers about 0.1 pc and 0.7 pc of the approaching and receding jets, respectively. A simple explanation for the asymmetric distribution is the existence of a thick plasma torus perpendicular to the jets. We also found an ambient FFA absorber, whose density profile can be ascribed to a spherical distribution of the isothermal King model. The coexistence of torus-like and spherical distributions of the plasma suggests a transition from radial accretion to rotational accretion around the nucleus.
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