Recombination Lines from Two Extended Sources in the Direction of the Galactic Center

Four recombination lines from hydrogen: lS6a, 166a, l67a, I68a, have been detected from the direction of the galactic center. The line profile is made up of two components: one at a velocity of +4 km s-i and the other at -57 km i; both are with respect to the local standard of rest. This line radiation originates from a spatially extended source or sources. The ratio of the peak antenna temperatures of these two velocity features varies with the principal quantum number, a fact which implies two physically different regions. At l66a the peak antenna temperatures are 0.65 K for the +4 km s-i feature and 0.300 K for the -57 km s-i feature. Comparisons with the H I absorption spectra toward Sgr A are discussed and a spatial coincidence for the recombination-line regions with the 0 and -53 km 1 neutralhydrogen features is suggested, although the possibility of their origin from H ii regions in the galactic center cannot be rejected.