Astronomy and Astrophysics – Astronomy
Scientific paper
Jan 1994
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1994phdt........35m&link_type=abstract
PhD Dissertation, Wisconsin Univ. Madison, WI United States
Astronomy and Astrophysics
Astronomy
Spatial Distribution, H Alpha Line, Ionized Gases, Interstellar Gas, Spectral Emission, H Ii Regions, H I Regions, Fabry-Perot Spectrometers, Ccd Cameras, Emission Spectra, Infrared Astronomy Satellite, Infrared Radiation
Scientific paper
Faint Galactic H alpha emission from the interstellar warm ionized medium (WIM) was observed with a dual-etalon, 150 mm-diameter, Fabry-Perot spectrometer (FWHM = 12 km/s) and a CCD camera (field of view approximately 0.8 deg). The spatial resolution of the images is 1-2 The observations were taken in 5 different locations in the Galaxy: (66, 0); (96, 0); (114, 0); (97.7, 26.7); and (116.5, 14.5). A high velocity (VLSR approximately -55 km/s), small feature, identified as the H II region BFS8, was discovered near l = 96 deg, b = 0 deg . An H alpha data cube shows that BFS8 has a diameter of about 12', an average surface brightness of approximately 13 Rayleighs, and a peak surface brightness of approximately 32 Rayleighs. The spatially integrated emission has a velocity FWHM approximately 32 km/s. The signal to noise ratio (SNR) for one pixel near the peak of the line is approximately 13. All of the images of the diffuse WIM H alpha show significant spatial variation in emission (i.e., structural features). The features range in size from 2' to 20'. The features' intensities within a particular region deviate from the mean intensity of that region by 15 to 50%. Analysis of the data shows that the structure in the H alpha images is primarily caused by emission and not by foreground extinction. Further, the two Galactic arms of regions (114, 0), and (116.5, -14.5) show no common structure, contrary to what would be expected if any of the structure is caused by foreground extinction. For region (97.7, 26.7), a correlation was found between the H alpha and IRAS infrared emissions. Since the infrared emission is also correlated with H I emission, this implies that H alpha and H I emissions are correlated for this region. No correlation between the H alpha and infrared emissions was found for region (116.5, 14.5). The diffuse ionized gas accounts for about 20% of the hydrogen gas in this direction. This lack of a correlation is not enough to show that this region is deficient in dust. Some of the features found in the H alpha images of the WIM may be faint, unidentified H II regions like BFS8. A possible way to identify such discrete sources or structural features due to foreground extinction would be to image the H alpha emission at several different velocities.
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