Astronomy and Astrophysics – Astronomy
Scientific paper
Dec 2006
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2006aas...209.1508r&link_type=abstract
2007 AAS/AAPT Joint Meeting, American Astronomical Society Meeting 209, #15.08; Bulletin of the American Astronomical Society, V
Astronomy and Astrophysics
Astronomy
Scientific paper
The source(s) of ionization and heating of the diffuse ionized gas in spiral galaxy disks and halos remains unclear. The usual optical diagnostic line ratios suffer from dependence on a confusing number of variables: not only the ionization state but also the temperature and abundance of the gas, as well as extinction, which is significant in some galaxies up to heights of 2 kpc above the plane. The Spitzer Space Telescope provides the opportunity to study the [Ne III]/[Ne II] mid-IR diagnostic, for which temperature, gas-phase abundance and extinction effects are unimportant. Here we report the first detection of these lines in an external spiral galaxy halo, and find that the ratio is enhanced relative to the disk a result which, as we also show, is problematic for pure photo-ionization models. We also report on the first spectroscopic detections of PAH features in an external galaxy halo. Their emission suggests rough scale-heights of 300-500 pc.
Benjamin Robert A.
Rand Richard J.
Wood Kathleen
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