74 MHz Discrete H ii Absorption Regions Toward the Inner Galaxy

Abstract

At low radio frequencies (< 100 MHz), classical HII regions may become optically thick (optical depth > 1) and can be observed as discrete absorption regions against the Galactic nonthermal background emission created by Galactic cosmic ray electrons spiraling around magnetic fields. In this work we present 74 MHz observations in the region 26>l>-15, -5