VLA observations of hydrogen and carbon recombination lines toward W3A at 1.4 GHz

We present high-sensitivity, high-resolution VLA observations of the W3 com plex of H H regions in the 168 alpha recombination lines of hydrogen, carbo n, and sulphur. The ii 168 alpha line from W3A consists of two components: a broad line (width similar to 27 km s(-1)) and a narrow line (width simila r to 7 km s(-1)). The narrow hydrogen and carbon line emissions over W3A, a lthough overlapping, are not entirely coextensive. The carbon line is possi bly correlated with the molecular gas near W3A. Stimulated emission is the main mechanism for the narrow hydrogen line emission. The width of the H-0 Line gives an upper limit of similar to 1000 K for the electron temperature of the partially ionized gas. The electron density ranges from 10 to 80 cm (-3) in the narrow hydrogen line region and from 10 to 60 cm(-3) in the car bon-line region. We determined the electron temperature of the classical H rr region W3A from the continuum brightness to be similar to 9000 K. The rm s n(e) of this H II region is similar to 2200 cm(-3), and the true n(e), de termined from a pressure-broadened profile of the H 171 eta (8.6 GHz) line, is similar to 2 x 10(4) cm(-3). Using these two values of electron densiti es, we determine a lower limit to the filling factor (0.01). Such a low val ue can be interpreted as an effect of density inhomogeneities in the medium .