TWISTING OF X-RAY ISOPHOTES IN TRIAXIAL GALAXIES

We investigate X-ray isophote twists created by triaxiality di†erences between the luminous stellar dis- tributions and the dark halos in elliptical galaxies. For a typically oblate luminous galaxy embedded in a more prolate halo formed by dissipationless collapse, the triaxiality di†erence of *T ^ 0.7 leads to typical isophote twists of at 3 e†ective stellar radii. In a model that includes bary- S*t X T ^ 16i ^ 19i onic dissipation, the e†ect is smaller, with *T ^ 0.3 and Thus, accurate measurements S*t X T ^ 5i ^ 8i. of X-ray isophote twists may be able to set constraints on the interactions between baryons and dissi- pationless dark matter during galaxy formation. The 30i X-ray isophote twist in the E4 galaxy NGC 720 cannot be reproduced by our model, suggesting an intrinsic misalignment between the halo and the stars rather than a projection e†ect. Subject headings: galaxies: individual (NGC 720) E galaxies: kinematics and dynamics E galaxies: structure E X-rays: galaxies