Intrinsic shapes of very flat elliptical galaxies

Abstract

Photometric data from the literature are combined with triaxial mass models to derive the variation in the intrinsic shapes of the light distribution of elliptical galaxies NGC 720, 2768 and 3605. The inferred shape variation is given by a Bayesian probability distribution, assuming a uniform prior. The likelihood of obtaining the data is calculated by using an ensemble of triaxial models. We apply the method to infer the shape variation of a galaxy, using the ellipticities and the difference in the position angles at two suitably chosen points from the profiles of the photometric data. The best‐constrained shape parameters are found to be the short‐to‐long axial ratios at small and large radii, and the absolute values of the triaxiality difference between these radii. The elliptical galaxies of our present investigation are very flat, with ellipticity typically around 0.3 or more. We find that the expectation values of the short‐to‐long axial ratio of these galaxies are around 0.5.

The Intrinsic Shape of Galaxy Bulges

“…In 2008, Chakraborty, Singh & Gaffar (2008) estimated the shapes of 10 elliptical galaxies with apparent ellipticities ε ≤ 0.3, finding that radial differences in the triaxiality parameter can be tightly constrained to values 0.29 < ∆ T < 0.54. Chakraborty, Diwakar & Pandey (2011) extended this analysis to 3 very flat galaxies with ellipticity ε ∼ 0.3 or more. They found values of the intrinsic flattening of these galaxies around F ∼ 0.5.…”

The Orientation of Elliptical Galaxy NGC 741

“…A triaxial generalization of [8] spherical density distribution ρ(r) is made triaxial by considering the distribution ρ(r) and replacing r by M, and its modify by [6],…”

“…Another form of triaxial generalization of [8] model is presented in [9] and its modified by [6]. Rewriting ρ(r) as f(r), the triaxial model is density distribution of the form…”

“…In above, g(r), h(r) and the parameters r 1 ..r 4 are the same as in [9]. g 1 (r) and h 1 (r) are introduced in [6], which for choices of parameter α>0, alter the profiles of ε and θ in the intermediate region.…”

“…The orientation of the individual elliptical galaxies have been investigated by [1], [2], [3] and [4].The methodology is based on Bayesian statistics, and is described in [5], [6] and more recently in [7]. The likelihood of obtaining the data from a model in a chosen orientation is a function of the view angle and the shape parameters.…”