WHAM observations of Hα , [S 2], and [N 2] toward the Perseus Arm: Probing the Physical Conditions of the WIM

Details WHAM observations of Hα , [S 2], and [N 2] toward the Perseus Arm: Probing the Physical Conditions of the WIM WHAM observations of Hα , [S 2], and [N 2] toward the Perseus Arm: Probing the Physical Conditions of the WIM

Dec 1998

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1998aas...193.8305h&link_type=abstract

American Astronomical Society, 193rd AAS Meeting, #83.05; Bulletin of the American Astronomical Society, Vol. 30, p.1377

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Scientific paper

A large region of the Galaxy toward the Perseus arm (l = 123\arcdeg to 164\arcdeg, b = -6\arcdeg to -35\arcdeg) has been mapped with the Wisconsin Hα Mapper (WHAM) in the [S 2] lambda 6716 and [N 2] lambda 6583 lines. By comparing this data with the maps from the WHAM Hα Sky Survey, we begin a global investigation of the physical properties of the Warm Ionized Medium (WIM) in the Galaxy. Several trends noticed in emission-line investigations of diffuse gas in other galaxies are confirmed in the Milky Way and extended to much fainter emission levels. In particular, we find that the [S 2]/Hα and [N 2]/Hα ratios increase as absolute Hα intensities decrease. Examining only the more distant Perseus arm emission, we find that the increase in these ratios is a strong function of b and thus, of height above the Galactic plane, z. We also find that the [N 2]/[S 2] ratio appears to be independent of Hα intensity---although a slight increase with z is also seen in this ratio. Scatter in this ratio appears to be physically significant and maps suggest regions with similar [N 2]/[S 2] ratios are spatially correlated. The large variation of [S 2]/Hα and [N 2]/Hα with nearly constant [N 2]/[S 2] may indicate variations in the local electron temperature. Such an interpretation suggests WIM temperatures that range from 6,000 K to 10,000 K, with regions having fainter Hα emission (and thus higher [S 2]/Hα and [N 2]/Hα ) at higher temperatures. The smaller variations in [N 2]/[S 2] may reflect changes in the local ionization conditions (which could affect S(++) /S(+) ) or in elemental abundance.

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