Multi-Array λ2 and 6cm Radio Continuum Observations of Sgr A West

Abstract

Sub-arcsecond (down to 0.1″ × 0.2″) radio continuum observations using the VLA² in a number of configurations have been carried out in order to investigate the fine-scale morphological details of the ionized gas and the distribution of spectral index along the triskelian-shaped figure of Sgr A West. In addition to finding a number of isolated patches of thermally-emitting gas and an absorbing feature at λ6cm within three arcminutes of the Galactic center, we have observed:

• 1) radio continuum emission from IRS-7, implying that the stellar wind from this supergiant is externally ionized. An improved position for this object was obtained.

• 2) the circular mini-cavity located along the east-west bar of Sgr A West. This feature has a diameter of 2-arcseconds and may have been created by a spherical wind, the source of which is yet to be identified; the seemingly most plausible candidate, IRS-16, is offset by 3″ from the center of the cavity.

Spectral index maps having a resolution of 0.7″ × 0.3″ were made from scaled array observations at λ2cm and 6cm. They show that the eastern arm has a spectral index near -0.1, while the northern arm and the bar have positive spectral indices, indicating perhaps a partial opacity effect. The spectral index of IRS-7 is +0.6, consistent with that expected from a completely ionized stellar wind.

National Research Council Resident Research Associate