2013ApJ...770..152W
Three-dimensional Geometries and the Analysis of H II Regions
Wood, Kenneth ( School of Physics & Astronomy, University of St Andrews, North Haugh, St Andrews, Fife, KY16 9AD, UK ; Department of Astronomy, University of Wisconsin-Madison, 475 N. Charter St., Madison, WI 53706, USA; ); Barnes, J. E. ( School of Physics & Astronomy, University of St Andrews, North Haugh, St Andrews, Fife, KY16 9AD, UK ); Ercolano, Barbara ( Universitts-Sternwarte Munchen, Scheinerstr. 1, D-81679 Munchen, Germany ); Haffner, L. M. ( Department of Astronomy, University of Wisconsin-Madison, 475 N. Charter St., Madison, WI 53706, USA ); Reynolds, R. J. ( Department of Astronomy, University of Wisconsin-Madison, 475 N. Charter St., Madison, WI 53706, USA ); Dale, J. ( Excellence Cluster "Universe," Boltzmannstr. 2, D-85748 Garching, Germany ) show affiliations
The Astrophysical Journal, Volume 770, Issue 2, article id. 152, 6 pp. (2013).
Published in Jun 2013
We compare emission line intensities from photoionization models of smooth and fractal shell geometries for low density H II regions, with particular focus on the low-ionization diagnostic diagram [N II]/Hα versus Hα. Building on previously published models and observations of Barnard's Loop, we show that the observed range of intensities and variations in the line intensity ratios may be reproduced with a three-dimensional shell geometry. Our models adopt solar abundances throughout the model nebula, in contrast with previous one-dimensional modeling which suggested the variations in line intensity ratios could only be reproduced if the heavy element abundances were increased by a factor of ~1.4. For spatially resolved H II regions, the multiple sightlines that pierce and sample different ionization and temperature conditions within smooth and fractal shells produce a range of line intensities that are easily overlooked if only the total integrated intensities from the entire nebula model are computed. Our conclusion is that inference of H II region properties, such as elemental abundances, via photoionization models of one-dimensional geometries must be treated with caution and further tested through three-dimensional modeling.
Keywords:
Free Keywords: Astrophysics - Galaxy Astrophysics; H II regions; ISM: abundances
Astronomy: H II regions; ISM: abundances
arXiv: Astrophysics - Galaxy Astrophysics
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