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Astron. Astrophys. 352, L36-L39 (1999)

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4. Conclusions

The B-, V-, and I-images of NGC 1288 taken with FORS were of such quality that we were enabled to carry out a quantitative analysis of the morphology of the galaxy. The analysis went trough two stages: first fitting an axisymmetric bulge/disk model to the data and then Fourier analyzing the residuals, which reflect the spiral arms. In this way the galaxy could be shown in an objective, quantitative manner to be multiple armed. From the bulge/disk model we have constructed a model rotation curve, which is scaled to the terminal circular velocity measured by Bottinelli et al. (1986). The resulting mass-to-light ratio is unrealistic large. Furthermore, arguments of density wave theory of swing-amplified shearing spiral arms lead to the theoretical expectation that according to the pure disk model NGC 1288 ought be to be a two-armed spiral, which is clearly contradicted by the observations. Both conclusions change, if a dark halo is introduced to the galaxy model. The mass-to-light ratio can then be shown to be comparable to that of other galaxies. Simultaneously the theoretically expected multiplicity of the spiral arms fits exactly to the observations. We conclude form this discussion that NGC 1288 is indeed surrounded by a dark matter halo.

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© European Southern Observatory (ESO) 1999

Online publication: November 23, 1999