Presentation #210.02 in the session “Feedback and the Interstellar Medium”.
The warm ionized medium (WIM) is one of the major components of the Galactic interstellar medium, where it accounts for roughly 20% of the total gas mass. Radio and FIR observations of ionized gas have revealed the presence of a component that is denser than the WIM. However, it is still unclear whether this denser component of the WIM (D-WIM), is related to the envelopes of HII regions, the ionized boundaries of molecular clouds or if it is a more compact and shorter lived version of the WIM or WIM compressed in the spiral arms of the Galaxy. In this talk I will present observations of low-frequency (<1 GHz) hydrogen radio recombination lines with the Green Bank Telescope, which are a powerful tool to determine the physical properties of the D-WIM and its relation with the WIM.