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We have introduced a new method of estimating the electron temperature anddensity of H II regions by using single dish observations. In this method,multiple hydrogen radio recombination lines of different bands are computedunder the assumption of low optical depth. We use evolutionary hydrodynamicalmodels of H II regions to model hydrogen recombination line emission from avariety of H II regions and assess the reliability of the method. According tothe simulated results, the error of the estimated temperature is commonly <13%, and that of the estimated density is < 25% for a < 1% uncertainty of theobserved line fluxes. A reasonable estimated value of electron density can beachieved if the uncertainty of the line fluxes are lower than 3%. In addition,the estimated values are more representative of the properties in therelatively high-density region if the gas density gradient is present in the HII region. Our method can be independent of the radio continuum observations.But the accuracy will be improved if a line-to-continuum ratio at millimeterwavelengths is added to the estimation. Our method provides a way to measurethe temperature and density in ionized regions without interferometers.

Determining electron temperature and density in a H II region by using the relative strengths of hydrogen radio recombination lines