We present direct measures of the ionization fractions of several sulfur ions in the Galactic warm ionized medium (WIM). We obtained high-resolution ultraviolet absorption-line spectroscopy of post-asymptotic giant branch stars in the globular clusters Messier 3 [(l, b) = (422, +787), d = 10.2 kpc, and z = 10.0 kpc] and Messier 5 [(l, b) = (39, +468), d = 7.5 kpc, and z = +5.3 kpc] with the Hubble Space Telescope and Far Ultraviolet Spectroscopic Explorer to measure, or place limits on, the column densities of S I, S II, S III, S IV, S VI, and H I. These clusters also house millisecond pulsars, whose dispersion measures give an electron column density from which we infer the H II column in these directions. We find fractions of?S+2 in the WIM for the M?3 and M?5 sight lines x(S+2) ≡ N(S+2)/N(S) = 0.33 ± 0.07 and 0.47 ± 0.09, respectively, with variations perhaps related to location. With negligible quantities of the higher ionization states, we conclude that S+ and?S+2 account for all of the S in the WIM. We extend the methodology to study the ion fractions in the warm and hot ionized gas of the Milky Way, including the high ions Si+3, C+3, N+4, and O+5. The vast majority of the Galactic ionized gas is warm (T ~ 104?K) and photoionized (the WIM) or very hot (T 4 × 105?K) and collisionally ionized. The common tracer of ionized gas beyond the Milky Way, O+5, traces 1% of the total ionized gas mass of the Milky Way.
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