Re-analysis of the Radio Luminosity Function of Galactic H II Regions

Abstract

We have re-analyzed continuum and recombination lines radio data available in the literature in order to derive the luminosity function (LF) of Galactic H II regions. The study is performed by considering the first and fourth Galactic quadrants independently. We estimate the completeness level of the sample in the fourth quadrant at 5 Jy, and the one in the first quadrant at 2 Jy. We show that the two samples (fourth or first quadrant) include, as well as giant and supergiant H II regions, a significant number of subgiant sources. The LF is obtained, in each Galactic quadrant, with a generalized Schmidt's estimator using an effective volume derived from the observed spatial distribution of the considered H II regions. The re-analysis also takes advantage of recently published ancillary absorption data allowing to solve the distance ambiguity for several objects. A single power-law fit to the LFs retrieves a slope equal to –2.23 ± 0.07 (fourth quadrant) and to –1.85 ± 0.11 (first quadrant). We also find marginal evidence of a luminosity break at L_(knee) = 10^(23.45) erg s^(–1) Hz^(–1) for the LF in the fourth quadrant. We convert radio luminosities into equivalent Hα and Lyman continuum luminosities to facilitate comparisons with extragalactic studies. We obtain an average total H II regions Lyman continuum luminosity of 0.89 ± 0.23 × 10^(53) s^(–1), corresponding to 30% of the total ionizing luminosity of the Galaxy.

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