**8.2. Isotropic Component**

Line emission and continuum processes from warm ionized gas in the
Galaxy also contribute an isotropic component to the DGL. For
|*b*| > 5°,
Reynolds (1992)
finds that H emission
strength matches the prediction of a path-length through a slab model
for the galaxy,
*I*(*H*)
2.9 ×
10^{-7} csc|*b*| ergs s^{-1} cm^{-2}
sr^{-1}. Fortunately,
H emission, specifically, is
irrelevant for us because the relative throughput of the F555W
bandpasses at H
(~ 6562Å) is only ~ 10% of the peak
filter throughput. The strongest
H emission expected in our
field would contribute 0.01 × 10^{-9}ergs s^{-1}
cm^{-2} sr^{-1} Å^{-1}, which corresponds
to 0.01% of the total background, and 1% of the expected EBL. The next
strongest line, [OIII] at 5007Å, is near the peak of
the F555W sensitivity, but it is fainter than
H by a factor of 20
(Reynolds 1985,
Shields *et al.* 1981)
and will contribute at most 0.05% of the expected EBL.

More important than line emission is the two-photon, free-free, and
bound-free continua emitted by ionized gas with the density implied
by the detected H
emission. The combined spectrum of
free-free, bound-free, and two-photon emission was calculated by
Aller (1987)
as a function of electron and ion densities, and has been expressed by
Reynolds (1992)
as a function of the observed
H
emission; it is a function of the temperature of the warm ionized
medium. For our purposes, a conservative estimates of the isotropic
continuum from gas with temperature *T* ~ 10^{4} is given by
Aller (1987) and
Reynolds (1992) as
*I*_{}( 3700Å) < 0.3 × 10^{-9}ergs
s^{-1} cm^{-2} sr^{-1} Å^{-1} and
*I*_{}( 3700Å) < 0.01 × 10^{-9}ergs
s^{-1} cm^{-2} sr^{-1} Å^{-1} (see
Aller 1987 and
Reynolds 1992
for discussion). We include these contributions in our estimate of the DGL.