Correlation between the Distribution of Diffuse Ionized Gas in the Galaxy and HII Regions

Abstract

The spatial correlation between HII region and diffuse ionized gas found earlier for the Hα line is confirmed using radio observations. In the inner part of the Galaxy, in the direction with coordinates l = 30°, b = 0°, the ionizing radiation from HII regions can propagate to distances ⩽240 pc, although 75% of this ionizing radiation arrives at mean distances of only ⩽7 pc. At the Galactic anti-center (l = 186.°6, b = 0.°32), the ionizing radiation of HII regions is able to ionize gas to distances of ⩽ 1300 pc, although 66% of this radiation ionizes gas at distances of ⩽155 pc. The relationship between the distributions of HII regions and diffuse ionized gas is used to derive the parameters of this gas in the direction of the pulsar B1758-23: emission measure 5800 ± 900 pc/cm⁶, mean electron density in clouds 5.42 cm⁻³, extent of the region occupied by clouds 200 pc, and filling factor for the electrons 0.06. The maximum contribution to the emission measure, dispersion measure, and scattering parameters of B1758-23 are made by a region at a distance of ≈1.3 kpc from the observer. The distance to PSR B1758-23 is found to be 3.5(+1, −0.3) kpc.