A high resolution HI absorption spectrum of SGR A.

The authors have used the VLA to obtain an H I absorption spectrum of the compact source Sgr A^* in the galactic nucleus at an angular resolution of 1arcsec.5. Absorption at 40 - 60 km s^-1 is present at an optical depth ≅0.25, as in the earlier, lower-resolution H I data (Liszt et al., 1983). The absence of such gas in the recent H₂CO absorption synthesis of Whiteoak et al. (1983) at 3arcsec.5 resolution must therefore be ascribed to peculiarities in the absorbing material and perhaps to the ≅130 times larger solid angle of Sgr A^* at λ21 cm. It cannot be due only to a background source geometry in which Sgr A^* is physically removed from the thermally-emitting material which appears to surround it.