Statistics
Scientific paper
Jan 1995
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1995phdt........11b&link_type=abstract
Thesis (PH.D.)--MASSACHUSETTS INSTITUTE OF TECHNOLOGY, 1995.Source: Dissertation Abstracts International, Volume: 56-06, Secti
Statistics
Dark Matter
Scientific paper
I have analyzed the X-ray-emitting gas in elliptical galaxies and galaxy clusters to probe their structure and dynamics. In addition to extending previous studies of detailed hydrostatic modeling of these systems, I have developed a new method to test for the existence of dark matter that is free from uncertainties in the temperature gradients and (in principle) does not require any model fitting. Applying these techniques to ROSAT PSPC data of the E4 galaxy NGC 720 I concluded that the dark matter distribution is highly elongated with ellipticity, epsilon~0.5-0.7; similar, but weaker, constraints are obtained for the E7/S0 galaxy NGC 1332. These results provide the first strong evidence for flattened halos in normal (i.e. no polar rings) ellipticals. I have also demonstrated that X-ray analysis of the aggregate shape of a galaxy cluster on scales of r~ 1-2 Mpc is insensitive to subclustering on small scales (_sp{~}< few hundred kpc). From analysis of ROSAT PSPC data of the aggregate shapes of five Abell clusters I concluded that they are quite elongated (epsilon ~ 0.40-0.55) and are consistent with the shapes traced by the galaxy isopleths. Finally, I have devised a method to quantitatively relate the morphologies of clusters to their dynamical states. Applying this method to ROSAT PSPC images of 55 clusters I find that the statistics of this method, power ratios, suggest an evolutionary track for the clusters; i.e. the location of a cluster along the track indicates the dynamical state of the cluster and the distribution of clusters along this track measures the formation and evolution of clusters in our sample. In principle power ratios can be used to address any problem where cluster evolution is an issue. (Copies available exclusively from MIT Libraries, Rm. 14-0551, Cambridge, MA 02139-4307. Ph. 617-253-5668; Fax 617-253-1690.).
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