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C. G. De Pree, M. C. Nysewander (Agnes Scott College), W. M. Goss (NRAO)
NGC 3576 (l = 291.3o, b = -0.7o) and NGC 3603 (l = 291.6o, b = -0.5o) are optically visible, luminous HII regions located at distances of 3.0 kpc and 7.7 kpc, respectively. We present 3.4 cm Australian Telescope Compact Array (ATCA) observations of these two sources in the continuum and the H90\alpha, He90\alpha, C90\alpha and H113\beta recombination lines with an angular resolution of 7\prime\prime and a velocity resolution of 2.6 km s-1. All four recombination lines are detected in the integrated spectra of the two sources. Broad radio recombination lines are detected in both NGC 3576 (\DeltaVFWHM \geq 50 km s-1) and NGC 3603 (\DeltaVFWHM \geq 70 km s-1). In NGC 3576 a prominent N-S velocity gradient (~30 km s-1 pc-1) is observed, and a clear temperature gradient (6000 K to 8000 K) is found from east to west, consistent with a known IR color gradient in the source. In NGC 3603, the H90\alpha, He90\alpha and the H113\beta lines are detected from 13 individual sources. The Y+ (He/H) ratios in the two sources range from 0.07±0.01 to 0.21±0.05. The H113\beta/H90\alpha ratio in NGC 3576 is close to the theoretical value, suggesting that local thermodynamic equilibrium (LTE) exists. This ratio is enhanced for most regions in NGC 3603, which may be the result of high optical depth or stimulated emission. We compare the morphology and kinematics of the ionized gas at 3.4 cm with the distribution of stars, 10\micron emission and H2O and CH3OH maser emission. These comparisons suggest that both NGC 3576 and NGC 3603 have undergone sequential star formation.