Other
Scientific paper
Apr 1997
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1997aps..apr..b603r&link_type=abstract
American Physical Society, APS/AAPT Joint Meeting, April 18-21, 1997, abstract #B6.03
Other
Scientific paper
Galactic Worms were first identified as irregular, vertical columns of atomic gas stretching from the Galactic plane. Similar structures are found in radio continuum and infrared maps. We have recently observed the radio recombination lines of H (and He) for a large number of positions away from the Galactic plane and classical H II regions. The recombination lines are detected from the brightest radio worms, demonstrating that the radio continuum emission is thermal. Further, we were able to measure the velocities of the ionized gas in the worms, and they agree with those of the giant H II regions in the galactic plane underneath them. The spectacular Galactic Worm in Aquila has been recently and extensively studied and shown to be associated with a concentration of H II regions. Another recently studied Galactic Worm is in the outer Galaxy, and numerous examples are being found in other galaxies. The existence of these structures has led us to consider that they may be responsible for a significant fraction of the diffuse ionized gas in the inner Galaxy. The source of the ionization in the inner galaxy is almost certainly hot stars, but the ionization state of He, as traced by the brightness of its radio recombination line, poses a problem. The observed, low ionization of He indicates that the ionizing spectrum is softer than those of stars hotter than O8, but without the hot stars there are not enough ionizing photons to balance the observed recombination rate of H. A possible explanation is that ionizing photons from hot stars are absorbed locally in compact H II regions; the relatively longer-lived, later O stars have their surroundings cleared by the supernovae and winds of the hot stars, allowing their ionizing photons to travel further.
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