A hydrogen and helium radio recombination-line survey of galactic H II regions at 10 GHz.
Abstract
The results of a radio recombination-line survey of 20 galactic H ii regions are used here as a diagnostic probe of the Oalaxy. At a frequency of 10.2 0Hz, we do not find appreciable departures from local thermodynamic equilibrium; each H ii region can be satisfactorily characterized by an average electron density and temperature. The nebular electron temperature is found to decrease monotonically by about 3000 K between 13 and 5 kpc from the galactic center. This Oalaxy temperature gradient most probably results from an increase in the heavy-element abundance by a factor of about 5 from 13 to 5 kpc from the galactic center. The observed temperature and suggested chemical gradients may extend to the galactic center, but observations from that region are difficult to interpret unambiguously. The ionized helium abundance also varies among different nebulae. However, since radio observations do not provide a reliable means of estimating the amount of neutral helium within H ii regions, it is not feasible to determine Oalaxy gradients in the total He/H ratio. Subject headings: galaxies: Milky Way - nebulae: abundances - nebulae: general - radio sources: lines.
- Publication:
-
The Astrophysical Journal
- Pub Date:
- April 1979
- DOI:
- 10.1086/156985
- Bibcode:
- 1979ApJ...229..524L
- Keywords:
-
- H Ii Regions;
- H Lines;
- Helium;
- Line Spectra;
- Milky Way Galaxy;
- Radio Astronomy;
- Abundance;
- Electron Energy;
- Nebulae;
- Radio Sources (Astronomy);
- Temperature Gradients;
- Astronomy;
- Galactic Structure;
- Galaxy:Element Abundances;
- Galaxy:H II Regions;
- H II Regions:Helium;
- H II Regions:Radio Radiation