Computer Science
Scientific paper
Sep 1990
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1990phdt........14e&link_type=abstract
Thesis (PH.D.)--YALE UNIVERSITY, 1990.Source: Dissertation Abstracts International, Volume: 51-07, Section: B, page: 3420.
Computer Science
6
Galaxies
Scientific paper
The nature of SO galaxies was studied by comparing the neutral hydrogen content and structural parameters of early type disk galaxies in three density regimes: low, intermediate and high densities as represented by the Karachentseva isolated sample, the Hydra cluster, and the Coma cluster. Two observing projects were undertaken: the first, a sensitive 21 cm. survey of massive early type disk galaxies done with the 300 m. Arecibo radio telescope; and the second, a CCD photometric study of B and R images of galaxies from the H I survey and from the three density regimes. The resulting surface brightness profiles were deconvolved into bulge and disk components where possible. The parameters derived from these projects were analyzed in the context of the parallel sequence system which classifies disk galaxies according to their bulge-to-total light ratio (B/T) (horizontally) and their disk structure (vertically). Although the Arecibo H I survey detected 48% of the SO's, 73% of the SOa's and 96% of the Sa's, few, if any, gas-rich galaxies would have gone undetected due to the inability of a 10 MHz bandwidth to detect a wide velocity spectral profile. A comparison of a hybrid, distance-independent H I surface density (M_{rm HI }/D_{rm opt} ^2) showed that the values for SO galaxies ranged continuously from amounts equivalent to those found in Sa's and Sb's, (10^9-10 10 solar masses) to low upper limits (<10^7 solar masses). The vertical axis of the classification system can thus be identified with a gradation in the neutral gas content, as well as with decreasing evidence of star formation activity. The variation of gas and structural properties along this axis is consistent with the evolution of Sa galaxies into SO's due only to astration. Although we find no strong evidence to support an environmental enhancement of this evolution, the distributions of B/T, total colors, disk colors, and (bulge-disk) colors are not inconsistent with a picture in which star formation in the Coma cluster galaxies ceased some time in the past whereas the SO disks in isolated environments have experienced a variety of star formation histories.
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