2001ApJ...546..447D

G315.4-2.3 is an extended-shell supernova remnant (SNR) with some characteristics of evolutionarily young remnants and some of older ones. To further elucidate some of its characteristics, we present imaging and polarimetry of this SNR at a frequency of 1.34 GHz with a resolution of 8" made with the Australia Telescope Compact Array. The indicators of youth are as follows: (1) morphologically, the radio emission arises in a smooth shell without the fine-scale filaments seen in the optical; (2) many of the optical filaments are Balmer dominated; (3) where measurable, the orientation of the magnetic field appears to be radial with respect to the center of the remnant; and (4) there may have been a supernova in that region in AD 185. Indications of older age include the following: (1) particularly in RCW 86, the bright optical nebula in the southwestern corner of this extended SNR, but also in other locations there are several filaments with bright [S II] emission representative of older shocked filaments in radiative equilibrium and (2) if the remnant lies at the kinematical distance of 2.8 kpc, it has a diameter of 37 pc which would be large for a remnant less than 2000 years old. The remnant seems to be expanding inside a cavity outlined by infrared emission, and so it could well be young and large. Where it is encountering the walls of the cavity it is slowing rapidly, and we observe the radiative filaments. RCW 86 itself is encountering a dense clump of material but may also be the remains of a more compact lump of ejecta ploughing into the surroundings.