Attempts have also been made to use shells as tracers of the mass distribution in ellipticals

Attempts have also been made to use shells as tracers of the mass distribution in ellipticals

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Attempts have also been made to use shells as tracers of the mass distribution in ellipticals. These structures result from merger with a low-mass disk. Since the disk is cold in one dimension, it wraps around the core ("phase-wrapping") and in projection gives sharp-edged shells alternating in sides (Quinn 1984, ApJ 279, 596). Applying a detailed model to the shells in real galaxies, Hernquist and Quinn (1987, ApJ 312, 1) found that the potential is quite deep (global M/L 100-200 ) and has a larger scale length than the stellar potential. This relies on the fact that the shell spacing is controlled by the potential: from their Fig. 3, for example, reproduced courtesy of the AAS, Planetary nebulae, pumping much of the radiation into a few emission lines, can be detected out to Virgo even from the ground. This lets us do emission-line kinematics on old stellar populations. The results are a mixed bag; Romanowsky et al. have found evidence that some
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