Mathematics – Logic
Scientific paper
Apr 1997
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1997phdt.........8r&link_type=abstract
Thesis (PHD). PRINCETON UNIVERSITY , Source DAI-B 57/10, p. 6308, Apr 1997, 172 pages.
Mathematics
Logic
Galactic Structure
Scientific paper
We discuss three topics: Stellar populations and Galactic structure at near infrared wavelengths; dust in gravitational lens systems, indicated by extreme optical-infrared colors; and small-scale correlations among faint extragalactic sources, interpreted as substructure in high redshift galaxies. We investigate the contributions of different stellar populations to the diffuse near infrared light of galaxies in two ways. First, we look for spatial variations in the strength of the 2.3μ m CO absorption feature in diffuse light from external galaxies. This feature arises in the atmospheres of cool stars, and is strongest in red supergiants, which are a young stellar population. Some (but not all) bright regions in galactic disks at λ ≃/ 2μ m are substantially due to young stars. Second, we measure the surface brightness contributed by giant stars in 49 fields in the plane of our Galaxy. These stars trace the old stellar population. We compare the distribution of giant star light to that of all near infrared light, and find that features in the total light are not always reflected in the giant star distribution. Both results indicate that near infrared light can be locally dominated by young stellar populations, and that features in near infrared light cannot be unambiguously interpreted as features in a galaxy's stellar mass distribution. Dust in gravitational lenses may hide lensed images from optical light surveys. If so, then the limits on the cosmological constant A derived from lensing can be relaxed. This would allow cosmological models with an older universe. We find that lens systems discovered in radio surveys have systematically redder optical-infrared colors than those found in optical surveys. They are also redder than unlensed radio sources. This suggests that dust is indeed present in gravitational lenses. Finally, we measure small scale angular correlations between sources in the Hubble Deep Field, finding strong correlations on scales ≤1''. These scales are at most a few kiloparsecs, regardless of source redshift, and must indicate physical association of objects. We argue that the observed effect can be explained as detection of substructure in galaxies at high redshift.
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