Figure 2: Relative emissivity of excess microwave emission to 100 μm FIR emission as a function of hydrogen column density, , for HII regions where an excess is detected. Data are shown for excess emission relative to spectra extrapolated using spectral indices fitted to lower frequency data (squares) and using canonical spectral indices for free-free emission (circles) for detections of anomalous microwave emission from Dickinson et al. (; blue points), Scaife et al. (; green points), RCW 175 (; red square), and G159.6–18.5 (; red square). A red dashed line indicates a relative emissivity of 10 μK typical of that observed on large scales at high galactic latitudes .