Other
Scientific paper
Jan 1995
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1995phdt........32s&link_type=abstract
Thesis (PH.D.)--THE UNIVERSITY OF MICHIGAN, 1995.Source: Dissertation Abstracts International, Volume: 56-12, Section: B, page:
Other
2
Supernovae, Stellar Winds
Scientific paper
The galactic fountain model predicts that energetic stellar winds and supernovae in OB associations produce superbubbles of hot gas that break out of the Galactic disk, cool radiatively as they rise upward, and recombine and return to the disk ballistically. The cool returning neutral hydrogen (H scI) is detectable as 21 cm emission from high-velocity clouds (HVCs), while the hot (T ~ 10^6 K) rising gas can be observed by X-ray telescopes. Very sensitive H scI observations of nearby disk galaxies were performed with the Arecibo 305 m radio telescope to measure the mass of HVCs in other galaxies. Ten of 14 galaxies have high-velocity wings that can be modeled as a component of galactic gas with a velocity dispersion of 30 or 50 km s^{-1}. The HVC mass for the 10 galaxies ranges from 6 times 10^7 M_&sun; to 4 times 10^9 M odot, which corresponds to 4 to 14% of the total H scI in the galaxies. This is the first survey to search for HVCs in more than a few galaxies, and the results imply that Galactic HVCs are a disk-wide phenomena with a characteristic distance of about 10 kpc. 21 cm synthesis imaging of UGC 12732 and NGC 5668, performed with the Very Large Array, confirmed the Arecibo results that the former does not have high-velocity gas while the latter does. Two components of high-velocity gas are present in NGC 5668; one may be from an accretion event, while the other is visible due to the increased H scI velocity dispersion throughout the optical disk and may be galactic fountain gas. Optical and IRAS observations of the 14 sample galaxies reveal that galaxies with high-velocity H scI wings have more active star-formation than galaxies without such wings, as would be expected if a substantial fraction of the HVCs are produced in galactic fountains. High-resolution X-ray observations of M33 were performed with the ROSAT satellite to search for superbubbles of hot gas within holes in the H scI layer in this nearby spiral galaxy. These observations revealed a number of X-ray point sources, diffuse X-ray emission around the nucleus of the galaxy, and two possible superbubbles. One has an X-ray luminosity of 2 times 1037 ergs s^{ -1} within an H scI hole of size 300 times 130 pc. The other has an X-ray luminosity of 8 times 1-37 ergs s^{-1} and a gas temperature of 2 times 10^6 K. It is coincident with the giant H scII region NGC 604 and is 13 +/- 13^' ^' from a 150 times 130 pc H scI hole.
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