Computer Science
Scientific paper
Oct 2001
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2001phdt..........z&link_type=abstract
Thesis (PhD). UNIVERSITY OF TORONTO (CANADA), Source DAI-B 62/04, p. 1905, Oct 2001, 181 pages.
Computer Science
5
Scientific paper
A systematic study of the molecular gas properties in strongly interacting galaxies (SIGs) has been undertaken, which includes two parts: (1)a statistical study of a large, optically-selected, complete sample of SIGs; (2)a case study of the nearest colliding pair NGC 4038/9 (``the Antennae'') with multi-transition data of both 12CO and 13CO. Consisting of 126 galaxies in 92 systems, our complete sample of SIGs includes all the SIGs in the northern sky with optical magnitude BT < 14.5. CO data have been collected for 95 SIGs (59 of which were observed by us) as well as for comparison samples of 59 weakly interacting and 69 isolated spiral galaxies. The statistical analysis of the samples shows that the SIGs, especially the colliding and merging systems, have a higher CO luminosity than isolated spiral galaxies. However, there is no significant difference in the atomic gas contents between the samples. This indicates that the excess CO emission is not due to the conversion of atomic gas to molecular gas, but may be more plausibly accounted for by a lower CO-to- H2 conversion factor X. For the Antennae galaxies, we have obtained high quality, fully sampled, single dish maps at 12CO J = 1-0 and 32 transitions with an angular resolution of 15' (1.5 kpc), together with 12CO J = 2-1, 13CO J = 2-1 and 3-2 data at selected regions with similar resolutions. Our Nobeyama 45m map recovers twice as much 12CO J = 1-0 flux as was reported by Wilson et al. (2000). The 12CO J = 1-0, 2-1 and 3-2 emission all peak in an off-nucleus region adjacent to where the two disks overlap. The 12CO/13 CO J = 2-1 and 3-2 integrated intensity ratios are remarkably high in the overlap region. Detailed LVG modeling indicates that the 12 CO and 13CO emission come from different spatial components. The 12CO emission originates from a nonvirialized low density gas component with a large velocity gradient. Such a large velocity gradient can produce ``over luminous'' CO emission, and the derived X factor is an order of magnitude lower than the conventional value. We suggest that the apparently strong CO emission in the overlap region of the Antennae galaxies is due to increased radiative efficiency, possibly because of the large velocity dispersion. A comparison of the CO J = 3-2 emission with the SCUBA 850 μm continuum in the Antennae galaxies shows that CO line emission on average contributes 46% of the 850 μm continuum flux and the ratio of 12CO J = 3-2 to SCUBA 850 μm flux varies by a factor of two across the system. After correcting for the 12CO J = 3-2 contamination, the dust emission at 850 μm detected by SCUBA is consistent with the thermal emission from a single warm dust component with a mass of 1.7 × 107 Msolar .
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