title: The nuclear region of the spiral galaxy M81.
abstract: Very-long-baseline radio interferometry images of the nuclear region of the nearby spiral galaxy M81 reveal the most compact galactic core outside the Galaxy of which the size has been determined: 700 x 300 astronomical units (AU). The observations exclude a starburst or supernova interpretation for the core. Instead they favor an active galactic nucleus. There is evidence for a northeastern jet bent by approximately 35 degrees over a length scale from 700 to 4000 AU. The jet is, on average, directed toward an extended emission region, probably a radio lobe, about 1 kiloparsec (kpc) away from the core. A corresponding emission region was found in the southwest at a distance of only 30 pc from the core. The observed jet is extremely stable and likely to be associated with a steady-state channel. There is no detectable motion along the jet beyond the nominal value of -60 +/- 60 km.s-1. The level of activities in the core region of M81 is intermediate between that of SgrA* and that of powerful radio galaxies and quasars.
authors.affiliation: Department of Physics and Astronomy, York University, North York, ON, Canada.
authors.forename: N
authors.initials: N
authors.lastname: Bartel
authors.forename: M F
authors.initials: MF
authors.lastname: Bietenholz
authors.forename: M P
authors.initials: MP
authors.lastname: Rupen