Computer Science
Scientific paper
Aug 2000
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2000noao.prop..207o&link_type=abstract
NOAO Proposal ID #2000B-0207
Computer Science
Scientific paper
In many spiral galaxies up to 40% of the H(alpha) luminosity arises from diffuse ionized gas (DIG). DIG forms the interface between the disk and the halo and is an important component of spirals. Photoionization, mainly by leakage from disk O stars, is the favored model for the DIG. By measuring line ratios we can constrain the ionization process. It is found that neither photoionization alone nor composite models consisting of photoionization and shock ionization (Rand 1998) explain the observed ratios. Based on results from the Wisconsin H Alpha Mapper (WHAM), Haffner et al. (1999) concluded that an additional electron heating mechanism must exist. Extra heating beyond that from photoionization would be the signature of an unrecognized process in the gaseous halos of galaxies. We propose a definitive observational test of the existence of such a heating process by observing [O II]/H(beta), [N II]/H(alpha) and [S II]/H(alpha) in selected galaxies. Because [O II] (lambda)3729Ahas a high excitation energy, its behaviour provides a definitive test of the extra heating hypothesis. These observations will also determine the amount of additional heating and thus constrain the possible mechanisms.
Ferguson Annette Mairi Nelson
Gallagher John S. III
Otte Birgit
Reynolds Ronald J.
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