Clues to the Mystery of the M31 Nucleus

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Session 49 -- Star Clusters in the Milky Way and Other Galaxies
Display presentation, Thursday, June 15, 1995, 9:20am - 4:00pm

[49.12] Clues to the Mystery of the M31 Nucleus

Ph. Crane (ESO/Garching)

HST imaging of the nucleus of M31 (Lauer et al. ,1993; King, Stanford, and Crane, 1995) revealed a double structure in which the brightest point in the V band(P1) is not centered on the outer isophotes but rather the fainter peak is. Interestingly, the fainter peak in V(P2) is the brightest point in the UV and is very close the center of the outer isophotes. The colour of P1 matches that of the reddened ''bowl'' of stars surrounding P2 found by King et al. Further complication is found in the spectra of the M31 nucleus (Bacon et al. ,1994) where the symmetric rotation curve shows no evidence of the brightest point P1. Additionally, the peak in the velocity dispersion does not lie at either of these peaks, but is shifted along the line joining them to the side of P2 away from P1. A simple model of the nucleus of M31 apparently can resolve these anomalies. The model assumes that P1 is a low velocity dispersion object in the gravitational field of P2. P2 and the surrounding stars rotate about a line perpendicular to the line joining P1 and P2. The model generates a 2-dimensional array of spectra using the HST imaging data as a reference for the brightness at each point. The models are convolved with a seeing function and then observed. The symmetry of the rotation curve is easily reproduced. The shift of the velocity dispersion curve is also produced. The model can restrict the range of velocity dispersions of P1, and the velocity of P1 relative to P2. The main objection to the model is that it implies that we are seeing P1 as it is being tidally disrupted in the field of P2. However, some evidence that this is indeed the case comes from the observation of the ''bowl'' of stars surrounding P2 mentioned above. \\ \\ Bacon et al. ,1994, A. \& A. 281,691.\\ Lauer et al. ,1993, A.J. 106,1436.\\ King, Stanford, and Crane, 1995, A.J. 109,164.

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