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Session 11 - Elliptical Galaxies.
Display session, Monday, June 10
Great Hall,
We derive the intrinsic shapes of the elliptical galaxies NGC 315, NGC 741, NGC 1052, NGC 3379, NGC 3665 NGC 4261, NGC 4472, and NGC 7626, by fitting dynamical models to photometric and stellar kinematic data from the literature. The models are constructed by solving the equation of continuity by separation in ellipsoidal coordinates (Statler 1994a,b). The parameters that are best constrained are the triaxiality of the total mass distribution, T, and the short-to-long axis ratio c_L. The inferred shape is given by a Bayesian probability distribution in the (T,c_L) plane. Photometric data are drawn from Peletier et al.\/ (1990) and kinematic data from Bender et al.\/ (1994), Binney et al.\/ (1990) and Davies et al.\/ (1988).
When NGC 741, NGC 3379, NGC 4261 and NGC 7626 are modeled the most probable shapes are strongly prolate with wide tails into the triaxial and even oblate parts of parameter space. When the four galaxies NGC 315, NGC 1052, NGC 3665 and NGC 4472 are modeled the most probable shapes are highly oblate with similar tails stretching into triaxial territory. By combining all of the normalized Bayesian distributions for the single galaxies into one data set an estimate of the parent distribution of elliptical galaxies can be calculated. Although the number of galaxies sampled is low there is some evidence to suggest that the parent distribution is bimodal with broad peaks at the oblate and prolate limits.
REFERENCES Bender, R., Saglia, R. P., amp; Gerhard O. E. 1994, MNRAS, 269, 785. Binney, J. J., Davies, R. L., amp; Illingworth, G. D. 1990, ApJ, 361, 78. Davies, R. L. amp; Birkinshaw, M. 1988, ApJS, 68, 409. Peletier, R. F., Davies, R. L., Illingworth, G. D., Davies, L. E., amp; Cawson, M. 1990, AJ, 100, 1091. Statler, T. S. 1994a, ApJ, 425, 458. Statler, T. S. 1994b, ApJ, 425, 500.
