HII regions identified with WMAPS and GLIMPSE

We find a total flux f_{nu}_=54211Jy and a flux from 88 sources of f_{nu}_=36043Jy. The bulk of the sources are at least marginally resolved, with mean radii ~60pc, electron density n_e_~9cm^-3^, and filling factor {Phi}HII~0.005 (over the Galactic gas disk).

We use GLIMPSE and Midcourse Space Experiment (MSX) 8um images to show that the bulk of the free-free luminosity is associated with bubbles having radii r~5-100pc, with a mean of ~20pc. These bubbles are leaky, so that ionizing photons emitted inside the bubble escape and excite free-free emission beyond the bubble walls, producing WMAP sources that are larger than the 8um bubbles. We suggest that the WMAP sources are the counterparts of the extended low density HII regions described by Mezger (1978A&A....70..565M).