Hydrogen and helium radio recombination-line survey of galactic H II regions at 10 GHz

Journal Article · Sun Apr 15 04:00:00 EST 1979 · Astrophys. J.; (United States)

DOI:https://doi.org/10.1086/156985· OSTI ID:6154392

Lichten, S M; Rodriguez, L F; Chaisson, E J

The results of a radio recombination-line survey of 20 galactic H II regions are used here as a diagnostic probe of the Galaxy. At a frequency of 10.2 GHz, 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 Galaxy 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 Galaxy gradients in the total He/H ratio.

• Research Organization: Harvard-Smithsonian Center for Astrophysics
• OSTI ID: 6154392
• Journal Information: Astrophys. J.; (United States), Journal Name: Astrophys. J.; (United States) Vol. 229:2; ISSN ASJOA
• Country of Publication: United States
• Language: English

Related Subjects

640105* -- Astrophysics & Cosmology-- Galaxies
71 CLASSICAL AND QUANTUM MECHANICS
GENERAL PHYSICS
COSMIC RADIO SOURCES
CRYOGENIC FLUIDS
ELECTROMAGNETIC RADIATION
ELEMENTS
ENERGY SPECTRA
EQUILIBRIUM
FLUIDS
GALAXIES
H2 REGIONS
HELIUM
HYDROGEN
LINE BROADENING
LINE WIDTHS
LTE
MILKY WAY
NEBULAE
NONMETALS
RADIATIONS
RADIOWAVE RADIATION
RARE GASES
RECOMBINATION
SPECTRA