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Title: Hα and [SII] emission from warm Ionized GAS in the Scutum-Centaurus Arm

We present Wisconsin H-Alpha Mapper [SII] λ6716 and Hα spectroscopic maps of the warm ionized medium (WIM) in the Scutum-Centaurus Arm at Galactic longitudes 310° < l < 345°. Using extinction-corrected Hα intensities (I{sub Hα}{sup c}), we measure an exponential scale height of electron density squared in the arm of H{sub n{sub e{sup 2}}}=0.30 kpc (assuming a distance of 3.5 kpc), intermediate between that observed in the inner Galaxy and in the Perseus Arm. The [S II]/Hα line ratio is enhanced at large |z| and in sightlines with faint I{sub Hα}{sup c}. We find that the [S II]/Hα line ratio has a power-law relationship with I{sub Hα}{sup c} from a value of ≈1.0 at I{sub Hα}{sup c}<0.2 R (Rayleighs) to a value of ≈0.08 at I{sub Hα}{sup c}≳100 R. The line ratio is better correlated with Hα intensity than with height above the plane, indicating that the physical conditions within the WIM vary systematically with electron density. We argue that the variation of the line ratio with height is a consequence of the decrease of electron density with height. Our results reinforce the well-established picture in which the diffuse Hα emission is due primarily to emission from in situ photoionizedmore » gas, with scattered light only a minor contributor.« less
Authors:
 [1] ; ;  [2] ;  [3] ;  [4]
  1. CSIRO Astronomy and Space Science, Marsfield, NSW (Australia)
  2. Department of Physics, University of Wisconsin-Whitewater, Whitewater, WI (United States)
  3. Department of Astronomy, University of Wisconsin-Madison, Madison, WI (United States)
  4. Department of Physics, University of Notre Dame, South Bend, IN (United States)
Publication Date:
OSTI Identifier:
22356798
Resource Type:
Journal Article
Resource Relation:
Journal Name: Astrophysical Journal; Journal Volume: 787; Journal Issue: 2; Other Information: Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
79 ASTROPHYSICS, COSMOLOGY AND ASTRONOMY; ATOMS; DUSTS; ELECTRON DENSITY; EMISSION; GALAXIES; PHOTOIONIZATION; VISIBLE RADIATION; WISCONSIN