NGC 3576 and NGC 3603: Two luminous southern HII regions observed at high resolution with the Australia telescope compact array

NGC 3576 (G291.28-0.71) and NGC 3603 (G291.58-0.43) are optically visible, luminous Pi II regions located at distances of 3.0 kpc and 6.1 kpc, respect ively. We present 3.4 cm Australia Telescope Compact Array (ATCA) observati ons 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 " and a velocity resolution of 2.6 km s(-1) All four recombination lines are detected in the integrated profiles of the two sources. Broad radio recomb ination lines are detected in both NGC 3576 (Delta V-FWHM greater than or e qual to 50 km s(-1)) and NGC 3603 (Delta V-FWHM greater than or equal to 70 km s(-1)). In NGC 3576 a prominent north-south velocity gradient (similar to 30 km s(-1) pc(-1)) is observed, and a clear temperature gradient (6000- 8000 K) is found from east to west, consistent with a known infrared color gradient in the source. In NGC 3603, the H90 alpha, He90 alpha, and the H11 3 beta lines are detected from 13 individual sources. The Y+ (He/H) ratios in the two sources range from 0.08 +/- 0.04 to 0.26 +/- 0.10. The H113 beta /H90 alpha: ratio in NGC 3576 is close to the theoretical value, suggesting that local thermodynamic equilibrium exists. This ratio is enhanced for mo st regions in NGC 3603; enhanced beta/alpha ratios in other sources have be en attributed to high optical depth or stimulated emission. We compare the morphology and kinematics of the ionized gas at 3.4 cm with the distributio n of stars, 10 mu m emission, and H2O, OH, and CH3OH maser emission. These comparisons suggest that both NGC 3576 and NGC 3603 have undergone sequenti al star formation.NGC 3576 (G291.28-0.71) and NGC 3603 (G291.58-0.43) are o ptically visible, luminous H II regions located at distances of 3.0 kpc and 6.1 kpc, respectively. We present 3.4 cm Australia Telescope Compact Array (ATCA) observations of these two sources in the continuum and the H90 alph a He90 alpha, C90 alpha, and H113 beta recombination lines with an angular resolution of 7 " and a velocity resolution of 2.6 km s(-1) All four recomb ination lines are detected in the integrated profiles of the two sources. B road radio recombination lines are detected in both NGC 3576 (Delta V-FWHM greater than or equal to 50 km s(-1)) and NGC 3603 (V Delta(FWHM) greater t han or equal to 70 km s(-1)). In NGC 3576 a prominent north-south velocity gradient (similar to 30 km s(-1) pc(-1)) is observed, and a clear temperatu re gradient (6000-8000 K) is found from east to west, consistent with a kno wn infrared 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 0.08 +/- 0.04 to 0.26 +/- 0 .10. The H113 beta/H90 alpha: ratio in NCC 3576 is close to the theoretical value, suggesting that local thermodynamic equilibrium exists. This ratio is enhanced for most regions in NGC 3603; enhanced beta/alpha ratios in oth er sources have been attributed to high optical depth or stimulated emissio n. We compare the morphology and kinematics of the ionized gas at 3.4 cm wi th the distribution of stars, 10 mu m emission, and H2O, OH, and CH3OH mase r emission. These comparisons suggest that both NGC 3576 and NGC 3603 have undergone sequential star formation.