Twisting of X-ray Isophotes in Triaxial Galaxies

We investigate X-ray isophote twists created by triaxiality differences between the luminous stellar distributions 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 difference of ∆T ≃ 0.7 leads to typical isophote twists of 〈∆ψX〉 ≃ 16 ± 19 at 3 stellar effective radii. In a model which includes baryonic dissipation the effect is smaller, with ∆T ≃ 0.3 and 〈∆ψX〉 ≃ 5 ± 8. Thus, accurate measurements of X-ray isophote twists may be able to set constraints on the interactions between baryons and dissipationless dark matter during galaxy formation. The 30 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 effect. Subject headings: galaxies: elliptical and lenticular, cD — galaxies: formation — galaxies: structure — galaxies: fundamental parameters — galaxies: individual (NGC 720) — X-rays: galaxies — dark matter