Statistics
Scientific paper
Jan 1996
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1996phdt........10s&link_type=abstract
Thesis (PH.D.)--THE UNIVERSITY OF WISCONSIN - MADISON, 1996.Source: Dissertation Abstracts International, Volume: 57-06, Sectio
Statistics
2
Scientific paper
O VI in the Interstellar Medium. The Copernicus O^{+5} column densities trace the 10^{5.5} K gas in the interstellar medium. We statistically re-analyze the dataset, including the possibility that local hot gas may contribute a significant O^{+5 } column density to most lines of sight. Our reanalysis includes slight improvements in the statistics and was found to be reliable when tested on simulated data sets. Our conclusions differ considerably from those of the original analysis and strongly influence the understanding of the interstellar medium, in particular the volume occupation of the hot and warm components, and mechanisms responsible for them. The Local Bubble column density compares favorably with the estimated quantity of O^{+5 } within the remnant of an ancient local explosion. Similarly, our mean O^{+5} column density per external feature agrees with models of hot interstellar bubbles from either stellar winds or ancient supernova explosions in a warm diffuse interstellar environment, suggesting that the hot gas in interstellar space may exist primarily within discrete regions of modest volume occupation rather than in a continuous and pervasive phase. Supernova Remnants in the Halo. High latitude observations of C^{+3} N^{+4}, and O ^{+5}, and the shadowing of high latitude x-ray emission by intervening hydrogen clouds indicate the presence of hot (~10 ^4 to 10^6K) gas in the halo of our galaxy. This project explores the contributions made by isolated supernova remnants. Their evolving structures were simulated with a hydrodynamic computer code. The results are intriguing. (1) At late times the remnants collapse faster than the high -stage ions can recombine. (2) The high-stage ions in the ensemble of remnants cover about ~50% of the sky. (3) The ensemble provides average column densities of >3.1 times 10 13 O^ {+5} atoms cm^{-2 }, >2.5 times 1012 N ^{+4} atoms cm^ {-2} and gg9.8 times 1012 C^{+3} atoms cm ^{-2}. The average O ^{+5} column density is 40% of the observed. The simulation ended before the ions had recombined, so additional contributions, especially for C^{+3}, are expected from later times. (4) The average x-ray contribution is ~50 ROSAT 1/4 keV counts s^ {-1} arcmin^{-2} versus observational estimates of 133 to 2660 ROSAT 1/4 keV counts s^{-1} arcmin^{-2}. (5) The average volume filled with hot (T > 10^6 K) gas is much smaller than that containing high-stage ions and is less than 1% of halo.
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