A critical review of the evidence for M32 being a compact dwarf satellite of M31 rather than a more distant normal galaxy - AstrophysicsReport as inadecuate




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Abstract: Since Baade-s photographic study of M32 in the mid 1940s, it has beenaccepted as an established fact that M32 is a compact dwarf satellite of M31.The purpose of this paper is to report on the findings of our investigationinto the nature of the existing evidence. We find that the case for M32 being asatellite of M31 rests upon Hubble Space Telescope HST based stellarpopulation studies which have resolved red-giant branch RGB and red clumpstars in M32 as well as other nearby galaxies. Taken in isolation, this recentevidence could be considered to be conclusive in favour of the existing view.However, the conventional scenario does not explain M32-s anomalously highcentral velocity dispersion for a dwarf galaxy several times that of eitherNGC 147, NGC 185 or NGC 205 or existing planetary nebula observations whichsuggest that M32 is more than twice as distant as M31 and also requires anelaborate physical explanation for M32-s inferred compactness. Conversely, wefind that the case for M32 being a normal galaxy, of the order of three timesas distant as M31, is supported by: 1 a central velocity dispersion typicalof intermediate galaxies, 2 the published planetary nebula observations, and3 known scaling relationships for normal early-type galaxies. However, thisnovel scenario cannot account for the high apparent luminosities of the RGBstars resolved in the M32 direction by HST observations. We are therefore leftwith two apparently irreconcilable scenarios, only one of which can be correct,but both of which suffer from potentially fatal evidence to the contrary. Thissuggests that current understanding of some relevant fields is still very farfrom adequate.



Author: C. K. S. Young, M. J. Currie, R. J. Dickens, A. L. Luo, T. J. Zhang

Source: https://arxiv.org/



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