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INTRINSIC SHAPES OF ELLIPTICAL GALAXIES: NGC 5638

    Department of Pure and Applied Physics, Guru Ghasidas Central University, Koni, Bilaspur Chhattisgarh, India- 495009

    arunkumarsingh20@yahoo.com

Abstract : We determine the intrinsic shapes of the light distribution of elliptical galaxies NGC 5638 and NGC 5813 by combining the profiles of photometric data from the literature with triaxial models. We use ensembles of models so that the shape estimates are largely model independent. We follow the methodology as described in Statler (1994) which is modified to suit our requirements. We find that short to long axial ratios at very small radii and at very large radii, and the absolute value of the triaxiality difference are the best constrained shape parameters. We use a modified prior as obtained from the shape estimates of a large sample of elliptical galaxies to determine the intrinsic shapes of the elliptical galaxies NGC 5638 and NGC 5813. Shape estimates using modified prior should be more reliable. These results are compared with the previous estimates which are determined by using flat prior reported by Chakraborty et al (2008) and Singh and Chakraborty (2009). The plot shows the intrinsic shapes of the NGC 5638 and NGC 5813 as a function of (q0,q∞) for two dimensional shapes and (q0,q∞,|Td|) for three dimensional shapes, where q0 and q∞(=q) are the short to long axial ratios at small and at large radii and |Td| is the absolute values of the triaxiality difference, defined as |Td|= |T∞ - T0|. The probability is shown in the dark grey region: darker is the region higher is the probability. We find that both the galaxies NGC 5638 and NGC 5813 are rounder inside and flatter outside.

Keyword : Intrinsic Shapes, Triaxial Models, Photometry, Elliptical and Galaxies.

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