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On the origins of the diffuse Hα emission: ionized gas or dust-scattered Hα halos?

Published online by Cambridge University Press:  05 March 2015

Kwang-Il Seon  and
Adolf N. Witt
Kwang-Il Seon
Affiliation:
Korea Astronomy and Space Science Institute, Daejeon 305-348, Korea
Adolf N. Witt
Affiliation:
Ritter Astrophysical Research Center, University of Toledo, Toledo, OH 43606, USA
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Abstract

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We find that the dust-scattering origin of the diffuse Hα emission cannot be ruled out. As opposed to the previous contention, the expected dust-scattered Hα halos surrounding H II regions are, in fact, in good agreement with the observed Hα morphology. We calculate an extensive set of photoionization models by varying elemental abundances, ionizing stellar types, and clumpiness of the interstellar medium (ISM) and find that the observed line ratios of [S II]/Hα, [N II]/Hα, and He I λ5876/Hα in the diffuse ISM accord well with the dust-scattered halos around H II regions, which are photoionized by late O- and/or early B-type stars. We also demonstrate that the Hα absorption feature in the underlying continuum from the dust-scattered starlight (“diffuse galactic light”) and unresolved stars is able to substantially increase the [S II]/Hα and [N II]/Hα line ratios in the diffuse ISM.

Keywords

ISM: generalHII regionsscattering
Type
Contributed Papers
Information
Proceedings of the International Astronomical Union , Volume 10 , Highlights H16: Highlights of Astronomy , August 2012 , pp. 576
Copyright
Copyright © International Astronomical Union 2015 

References

Zurita, A., Beckman, J. E., Rozas, M., & Ryder, S. 2002, A&A 386, 801Google Scholar
Seon, K.-I. 2009, ApJ 703, 1159CrossRefGoogle Scholar