3 Free - Free Signal

This document provides a brief summary estimate of Galactic free-free emission and Hα emission and their relationship. Particular emphasis is placed on estimating the potential freefree emission in the region of significant confusion for CMB anisotropy measurements. Existing x-ray, ultraviolet and Hα emission provide limits on the radio free-free emission and vice versa. These limits are generally somewhat smaller than the observed “free-free” (signal ∝ ν) microwave signal. If these preliminary results true, then some previously neglected source may be present. Physics argues that Hα emission is still the best tracer for Galactic free-free emission and thus a tool for diagnosing if there is a previously neglected source.