Computer Science
Scientific paper
Dec 2002
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2002phdt........15b&link_type=abstract
Thesis (PhD). UNIVERSITY OF HAWAI'I, Source DAI-B 63/06, p. 2873, Dec 2002, 170 pages.
Computer Science
Scientific paper
We present an atlas of infrared images and photometry for an optically-selected, magnitude-limited sample of 77 spiral and S0 galaxies chosen from the Revised Shapley- Awes Catalog. This data includes JHK photometry, 12 μm ISOCAM images, and ISOPHOT photometry at 60, 100, and 180 μm that is supplemented with 450 and 850 μm photometry when available. Following an analysis of the properties of the sample galaxies, we have compared the mid-infrared and far- infrared ISO photometry with IRAS photometry. The systematic differences we find between the IRAS Faint Source Catalog and ISO measurements are directly related to the spatial extent of the ISO fluxes, and we discuss the reliablility of IRAS Faint Source Catalog total flux densities and flux ratios for nearby galaxies. Using mid-infrared and far-infrared flux densities normalized by K-band flux densities as indicators of recent star formation, we find several trends. First, star formation activity is stronger in late-type (Sc - Scd) spirals than in early-type (Sa - Sab) spirals. Second, infrared emission and therefore star formation is significantly more extended in later-type spirals than in early-type spirals. We also search for trends in nuclear star formation related to the presence of a bar or nuclear activity. Nuclear star formation activity is not significantly different between barred and unbarred galaxies, but it does appear to be inhibited in LINERS and transition objects compared to H II galaxies. For the 71 galaxies where we had complete 60 180 μm data, we fit blackbodies with λ-1 emissivities and average temperatures of 31 K or λ-2 emissivities and average temperatures of 22 K. For the eight galaxies where we had submillimeter data, we fit blackbodies with λ-1, λ-2 , and λ-β (with β variable) emissivities to the data. The best results were with the λ-β emissivities, where the temperatures varied from 30 35 K and the emissivity coefficients ranged from 0.9 to 1.9. These results produced gas to dust ratios that ranged from 150 to 580, which were consistent with the ratio for the Milky Way and which exhibited little dispersion.
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