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Title:Gas distribution, star formation and giant molecular cloud evolution in nearby spiral galaxies
Author(s):Rebolledo Lara, David
Director of Research:Wong, Tony
Doctoral Committee Chair(s):Wong, Tony
Doctoral Committee Member(s):Gammie, Charles F.; Chu, You-Hua; Looney, Leslie W.
Department / Program:Astronomy
Degree Granting Institution:University of Illinois at Urbana-Champaign
Interstellar Medium (ISM)
Molecular Clouds
Star Formation
NGC 6946
NGC 628
Abstract:In this thesis, I present a detailed study of the resolved properties of the cold gas in nearby galaxies at different size scales, starting from the whole galactic disk to the size of the Giant Molecular Clouds (GMCs). Differences in the shape and width of global CO and HI spectra of resolved disks of spiral galaxies are systematically investigated using a nearby sample for which high-resolution CO and HI maps are available. I find that CO line widths can be wider than HI widths in galaxies where the rotation curve declines in the outer parts, while they can be narrower in galaxies where the CO does not adequately sample the flat part of the rotation curve. Limited coverage of the CO emission by the telescope beam can mimic the latter effect. A physically based prescription linking the CO and HI radial profiles with the stellar disk is consistent with these findings. Then, I present an analysis performed on high spatial resolution observations of Giant Molecular Clouds in the three nearby spiral galaxies NGC 6946, NGC 628 and M101 obtained with the Combined Array for Research in Millimeter-wave Astronomy (CARMA). Using the automated CPROPS algorithm I identified 112 CO cloud complexes in the CO(1-0) map and 145 GMCs in the CO(2-1) maps. The properties of the GMCs are similar to values found in other extragalactic studies. Clouds located on-arm present in general higher star formation rates than clouds located in inter-arm regions. Also, I find differences in the distribution of star formation efficiencies in the disk of these galaxies. These differences may be related to the underlying dynamical process that drives the observed spiral arm structure in the disks. In this scenario, in galaxies with nearly symmetric arm shape (e.\ g., NGC 628), the spiral shocks are triggering star formation along the arms. On other hand, galaxies with flocculent or multi-arm spiral structure (e.\ g., NGC 6946 and M101) show regions of high star formation efficiency at specific regions of the spiral arms, as the result of gas flow convergence or regions where previous spiral arms may have collided.
Issue Date:2014-01-16
Rights Information:Copyright 2013 David Rebolledo Lara
Date Available in IDEALS:2014-01-16
Date Deposited:2013-12

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