The King model incorporates a core radius which has interesting dynamical implications

The King model incorporates a core radius which has interesting dynamical implications

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The King model incorporates a core radius which has interesting dynamical implications. Some ellipticals (such as M87) have unmistakeable cores, within which the intensity distribution is nearly flat, while others show scale-free profiles to the limit of even HST resolution. When distinct cores are present, they are very seldom of a pure King-law form, flattening toward zero central slope, as shown in Fig. 6 of Lauer 1985 (ApJ 292, 104) (reproduced below by permission of the AAS). Driven by extensive HST imaging of galaxy cores, Lauer et al. (1995 AJ 110, 2622) have introduced a more complicated form, the "Nuker" profile, to represent such cores as two asymptotic power laws - an outer one of slope β and an inner one of slope -γ shading into one another (over an area controlled by a parameter α) at a characteristic break radius r b : This law may fail for large radii, where most ellipticals are well described by the r 1/4 law (which itself corresponds to a Nuker law with α = 1/4, γ =0, and limits
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The King model incorporates a core radius which has interesting dynamical implications

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