THE PARSEC-SCALE RADIO STRUCTURE OF NGC 1068 AND THE NATURE OF THE NUCLEAR RADIO SOURCE

摘要: We present sensitive, multifrequency Very Long Baseline Array (VLBA) images of the nuclear radio sources NGC 1068. At 5 and 8.4 GHz, continuum source S1, argued to mark location hidden active nucleus, resolves into an elongated, ~0.8 pc oriented nearly at right angles jet axis but more closely aligned distribution H2O maser spots. S1 is detected GHz not 1.4 indicating strong free-free absorption below it has a flat spectrum between GHz. A 5-8.4 spectral index map reveals unresolved, inverted center structure that may AGN proper. The average brightness temperature too low for synchrotron self-absorption impact integrated significantly. In addition, careful registration with masers argues arises from inner regions disk rather than jet. emission mechanism be direct, thermal X-ray-heated corona or wind arising molecular disk. demonstrate nucleus sufficiently luminous, within current estimates, provide requisite heating. components C S2 both show evidence compact, steep-spectrum source. might arise shock cocoon enveloping compact sources. presence specifically component supports interpretation jet-ISM interaction. Component NE remains on VLBA baselines appears local enhancement emissivity reason clear; region surrounding virtually devoid narrow-line filaments, so there no clear interaction ISM. instead in internal perhaps denser plasma broke away earlier circumnuclear