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Nebular excitation of low-luminosity emission nuclei

Published online by Cambridge University Press:  24 November 2004

Joseph C. Shields
Affiliation:
Department of Physics & Astronomy, Ohio University, Athens, OH 45701, USA e-mail:[email protected]
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Abstract

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Low-luminosity nebular emission is found in the centers of a large fraction of galaxies, and in many cases the energy source powering these systems is ambiguous. This is particularly true for H II/LINER “transition” objects, although a reasonable explanation for these sources is that their emission is the composite result of a weak accretion-powered system surrounded by star-forming regions. This contribution describes results from a Hubble Space Telescope spectroscopic survey that probes the structure of nearby transition objects and other emission nuclei. The results provide only limited support for the composite picture for these sources; the emission nuclei do not show a strong tendency for the nebular classification to depend on aperture size. The strongest variations in forbidden line ratios appear to be mediated by a gradient of decreasing nebular density with increasing radius.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

Type
ORAL CONTRIBUTIONS
Copyright
© 2004 International Astronomical Union