Radio Recombination Lines
Radio recombination lines (RRLs) are important diagnostic tools in the determination of the physical conditions in HII regions. Temperatures in the HII regions, rms electron densities, the excitation temperature of the exciting stars are examples of the possible properties that can be determined. H and He RRLs can be used to determine the He/H abundance in the HII region and estimate the enrichment of He with metallicity. C RRLs can be used to probe the physical conditions in the photo-dissociation regions.
Below is an image of the Galactic distribution of nebular electron temperatures produced from the discrete HII regions located between Galactic azimuth 330 deg and 60 deg using the GBT. The contours range between 6400 and 11200 K at intervals of 400 K. The darker shades are lower temperatures. The orientation has the Galactic Center located at (x = 0, y = 0) and the Sun at 8.5 kpc above the Galactic Center at zero azimuth. The points indicate the location of the discrete HII regions. (See Balser et al. 2011.)
Modified on Tuesday, 28-Feb-2012 12:54:41 EST