The Arc and other structures in the Center of M81

Details The Arc and other structures in the Center of M81 The Arc and other structures in the Center of M81

Sep 1996

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1996aj....112.1021k&link_type=abstract

Astronomical Journal v.112, p.1021

Astronomy and Astrophysics

Astronomy

14

Galaxies: Individual: M81, Radio Lines: Galaxies, Galaxies: Nuclei, Galaxies: Seyfert

Scientific paper

Multi-configuration VLA λ6 cm and λ20 cm radio continuum observations of the extended emission surrounding the mini-Seyfert nucleus of M81 are presented and compared with optical emission-line images and with near-IR images. The extended radio emission is dominated by a large, highly polarized, nonthermal arc with a projected length of 0.9 kpc in the plane of the sky and centered 45" (0.8 kpc) northeast of the nucleus. The radio arc, which has no apparent optical counterpart, is connected by three bridges to the extended emission of the central source. The two outer bridges give the arc the appearance of a giant loop coming off the central source; the middle bridge has a nonthermal spectral index. In the arc, the magnetic field perpendicular to the line- of-sight is parallel to the curve of the arc. Most likely, the arc is highly inclined to the plane of the thermal gas and its shape is governed by magnetic and cosmic-ray pressures. It may be a large-scale version of the Galactic Center Lobe in the center of the Milky Way or a small-scale version of the nuclear radio lobes extending perpendicular to the disk in certain edge-on Seyfert galaxies. The middle bridge and a nonthermal "little jet" (2.5"=44 pc long) at the nucleus line up at a position angle of -30^deg^ and could be supplying cosmic ray electrons to the arc. In addition, two oval structures are detected in the radio continuum. The larger one coincides with the near-infrared mini-bar. The smaller one (possibly an inclined gas disk) has a different position angle and no near-infrared counterpart. A prominent radio continuum filament extends west from the northern major axis of the smaller oval but does not correspond to either an Hα filament or an obvious dust lane.

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