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H Emission at High Galactic Latitudes
R. J. Reynolds
University of Wisconsin-Madison, USA
Thermal bremsstrahlung emission from the warm ionized compo-
nent of the interstellar medium is one of the principal Galactic
foregrounds contaminating observations of the cosmic microwave
background. Under the peak of the CMB the intensity of this
emission may be comparable to or greater than that of the Galac-
tic synchrotron and thermal dust emission. However, because it
does not dominate the light from the sky at any wavelength, its an-
gular distribution over the sky cannot be mapped directly. Within
the last few years, surveys of diuse interstellar H emission have
been undertaken to explore the warm ionized interstellar gas. At
high Galactic latitudes, where interstellar extinction of the opti-
cal H is small, the relationship between the intensity of the H-
recombination line and the free-free continuum is only a function
of the electron temperature. Therefore, since the temperature of
the gas is tightly constrained, these high latitude H surveys can
provide accurate maps of the Galactic free-free emission. More-
over, by characterizing the free-free, these H observations may
also play a useful role in investigating the degree to which spinning
dust grains contribute to the foreground mm wave emission. The
Wisconsin H Mapper (WHAM) survey, completed in 1998, has
sampled the sky north of declination 30 o at about one degree
angular resolution (Haner et al 2000). Higher angular resolution
surveys of both the southern and northern hemispheres are also
in progress (Gaustad et al 1997; Dennison et al 1998).
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