NOAO >   Observing Info >   Approved Programs >   2001B-0285

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Proposal Information for 2001B-0285


PI: J. Gerssen, Space Telescope Science Institute, gerssen@stsci.edu
Address: 3700 San Martin Drive, Baltimore, MD 21218, USA

CoI: R.P. van der Marel, Space Telescop Science Institute
CoI: M.R. Merrifield, University of Nottingham, UK

Title: Secular Evolution of Galactic Disks

Abstract: Stellar velocity dispersions increase over the lifetime of stars and this leads to a thickening of galactic disks. However, the processes behind this phenomenon are uncertain. A simple diagnostic for ascertaining the ``heating'' mechanism is provided by the ratio of the vertical-to-radial stellar velocity dispersions. We have developed a technique for measuring this ratio and successfully applied it to two galaxies (NGC 488 and NGC 2985). These results, combined with the solar neighborhood value, hint at trend with galaxy morphology, in the sense that the ratio decreases along the Hubble sequence. This relation is implicitly predicted by the existing disk heating theory. We propose to triple the sample size of galaxies for which the velocity ellipsoid is measured. Such a sample will unequivocally establish the validity of the current disk heating theories. In addition, the sample will also clarify whether the secular evolution of galactic disks is indeed a function of morphological type.


National Optical Astronomy Observatory, 950 North Cherry Avenue, P.O. Box 26732, Tucson, Arizona 85726, Phone: (520) 318-8000, Fax: (520) 318-8360



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