An exploration of the heterogeneous nature of the warm ionized medium in the Galaxy

Details An exploration of the heterogeneous nature of the warm ionized medium in the Galaxy An exploration of the heterogeneous nature of the warm ionized medium in the Galaxy

Oct 2004

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2004phdt........24m&link_type=abstract

Ph.D dissertation, 2004. 151 pages; United States -- Wisconsin: The University of Wisconsin - Madison; 2004. Publication Number

Computer Science

5

Warm Ionized Medium, Galaxy, Interstellar Medium, Diffuse Ionized Gas

Scientific paper

To better understand the nature and origin of the warm ionized medium (WIM) in and near the Galaxy, we discuss three projects based on observations obtained with the Wisconsin H-Alpha Mapper.
First, we analyze the emission lines of [N II] l6583, [N II] l5755, [S II] l6716, [O III] l5007, and He I l5876 toward several classical O star H II regions, and a variety of newly revealed faint, large-scale Ha-emitting structures that span a wide range in surface brightness, scale, environment, and morphology. We compare the relative intensities of these lines to explore the temperature and ionization conditions within the emitting gas and their variations between the different emission regions. We find that in the WIM, the gas is warmer, in a lower ionization state, and ionized by a softer spectrum than the gas in classical H II regions surrounding O stars. We also find that the large filamentary structures are regions of higher density compared to the more diffuse WIM.
Second, we investigate emission from ionized gas near the Galactic plane toward a large, low extinction window into the inner Galaxy, out to the tangent point at [Special characters omitted.] ~ 6 kpc. We find a scale height and r.m.s. midplane density of the gas that increases from [approximate]180 pc and 0.5 cm -3 at R G ~ 6 kpc to [approximate]300 pc and 1.1 cm -3 at R G ~ 4 kpc. Within [Special characters omitted.] [approximate] 4 kpc, the extinction per unit neutral gas column density, E ( B - V )/ N H , is near the local value and increases toward the inner Galaxy. We also find evidence for an increase in temperature and ionization state with increasing | z | in the inner Galaxy.
Third, we present a search for the intergalactic ionizing radiation field through observations near and off the edge of the southwestern H I disk of M31. Beyond the bright stellar disk, but within the H I disk, weak Ha is detected with an intensity I Ha = [Special characters omitted.] R, implying that the ambient intergalactic Lyman continuum flux onto each side of M31 is F LC <= 1.6 x 10 4 photons cm -2 s -1 . This flux is too weak to account for the Ha emission from high velocity H I clouds in the Milky Way halo and Magellanic Stream.

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