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Étude de la transition entre le gaz atomique et le gaz moléculaire dans deux cirrus de la boucle céleste nord
| Content Provider | Semantic Scholar |
|---|---|
| Author | Barriault, Léo |
| Copyright Year | 2010 |
| Abstract | The infrared (IR) cirrus clouds observed at high Galactic latitude are excellent candidates to study the transition between the atomic gas and the molecular gas. In this thesis, two potential sites of H2 formation have been discovered in the North Celestial Loop (/ = 135°, b = 40°) through examining the far-IR-Hl ratio and looking for an excess over that expected from an atomic medium. I call these sites the Spider and Ursa Major fields. The comparison between the IR excess map and the CO (J — 1 — 0) data from the Five College Radio Astronomical Observatory (resolution = 45 arcsec) shows that the IR excess peaks do not coincide with the CO peaks. The absence of coincidence is explained by (i) a density too small to allow CO excitation, (ii) insufficient CO self-shielding or (iii) variations of the dust properties. The comparison between CO data and Hi data from the Dominion Radio Astrophysical Observatory (resolution = 1 arcmin) is in agreement with the models that predict CO formation where large velocity shears and turbulence dissipation are observed. OH observations of 108 locations over the two diffuse clouds from the Green Bank Telescope (resolution = 7 arcmin) are analyzed. OH is a precursor molecule to CO and its formation requires H2. The coincidence between the OH emission peak and the IR excess peak indicates that OH could be a better tracer of H2 than CO in these low-density regions. CO (7 = 1-0) and CO (J = 1 0 ) observations from the Institut de Radioastronomie Millimétrique and CO ( J = 2 — 1) observations from the James Clerk Maxwell Telescope (resolution = 20 arcsec) are analyzed on a small number of fields in both regions. Using a large velocity gradient model, we found smaller densities at the location of the IR excess peak while self-shielding should be efficient given the computed column densities. |
| File Format | PDF HTM / HTML |
| Alternate Webpage(s) | https://corpus.ulaval.ca/jspui/bitstream/20.500.11794/21631/1/27486.pdf |
| Language | English |
| Access Restriction | Open |
| Content Type | Text |
| Resource Type | Article |
