A Multiwavelength Optical Emission Line Survey of Warm Ionized Gas in the Galaxy

We report on observations of several optical emission lines toward a variety of newly revealed faint, large-scale Ha-emitting regions in the Galaxy. The lines include [N II] l6583, [N II] l5755, [S II] l6716, [O III] l5007, and He I l5876 obtained with the Wisconsin Ha Mapper (WHAM) toward sight lin...

Full description

Saved in:
Bibliographic Details
Published in:The Astrophysical journal 2006-11, Vol.652 (1), p.401-425
Main Authors: Madsen, G. J, Reynolds, R. J, Haffner, L. M
Format: Article
Language:English
Subjects:
Astronomy
Earth, ocean, space
Exact sciences and technology
Citations: Items that this one cites
Items that cite this one
Online Access:Get full text
Tags: Add Tag
No Tags, Be the first to tag this record!
Description
Summary:We report on observations of several optical emission lines toward a variety of newly revealed faint, large-scale Ha-emitting regions in the Galaxy. The lines include [N II] l6583, [N II] l5755, [S II] l6716, [O III] l5007, and He I l5876 obtained with the Wisconsin Ha Mapper (WHAM) toward sight lines that probe superbubbles, high-latitude filamentary features, and the more diffuse warm ionized medium (WIM). Our observations include maps covering thousands of square degrees toward the well-known Orion-Eridanus bubble, a recently discovered 60 x 20 bipolar superbubble centered in Perseus, plus several classical H II regions surrounding OB stars and hot evolved stellar cores. We use the emission-line data to explore the temperature and ionization conditions within the emitting gas and their variations between the different emission regions. We find that in the diffuse WIM and in the faint high-latitude filamentary structures the line ratios of [N II]/Ha and [S II]/Ha are generally high, while [O III]/Ha and He I/Ha are generally low compared to the bright classical H II regions. This suggests that the gas producing this faint widespread emission is warmer, in a lower ionization state, and ionized by a softer spectrum than gas in classical H II regions surrounding O stars, the presumed ionization source for the WIM. In addition, we find differences in physical conditions between the large bubble structures and the more diffuse WIM, suggesting that the ionization of superbubble walls by radiation from interior O associations does not account entirely for the range of conditions found within the WIM, particularly the highest values of [N II]/Ha and [S II]/Ha.
ISSN:0004-637X
1538-4357
DOI:10.1086/508441