This paper presents a "geometric" test of MOND, checking whether the mass distribution implied by X-ray data follows from that of the stars. The answer seems to be Close, but No Cigar. (This is the same result obtained earlier for the same galaxy in paper [77], but now with better data from Chandra in which the perplexing pointiness of the X-ray isophotes found with ROSAT has gone away.)

The new data do show a significant is small (~20 degree) change of position angle between X-rays and the optical light, though it is instructive to view Fig. 1 and judge for oneself. There is also a slight offset between X-ray ellipticities and that predicted from mass-follows-light, though this doesn't seem to become significant until near the radius where one infers that something odd must be going on with dark matter as well. The radial mass profile is consistent with rho ~ r-2, as would be expected if MOND dynamics were interpreted in terms of dark matter.

While data can always be improved, I don't think data quality is really the issue here. I am skeptical of the assumption in the analysis of perfect hydrostatic equilibrium. If we insist on this, the results seem just as odd in the context of dark matter as in MOND. That there is a shift in position angle at large radius seems to suggest that the system is not in equilibrium in either case. This isn't too surprising, as dynamical measurements imply that modest deviations from equilibrium are common at large radii in elliptical galaxies (Gerhard et al., e.g., paper 129.)

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