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Astron. Astrophys. 345, 36-42 (1999)

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4. NGC 1560 as another selected case

In order to test the capacity of MOND to reproduce the detailed shape of the rotation curves is presented here the fit for the rotation curve of the galaxy NGC 1560 at the maximum distance to ensure at least stability in the gaseous disc. This galaxy is very interesting because it presents a remarkable structure in its rotation curve.

NGC 1560 is a dwarf spiral galaxy which satisfied the criteria of selection proposed by Begeman et al. (1991) to ascertain that the rotation curve is a good tracer of the radial force. The gas is smoothly distributed and reasonably symmetric with respect to the center, and [FORMULA] (Broeils 1992). The MOND fit reproduces successfully the observed curve structure for the adopted distance of 3.0 Mpc (the distance estimates for this galaxy range from 2.9 to 3.7 Mpc). The Toomre parameter of the gaseous disc was calculated with [FORMULA] km/s and is plotted in Fig. 3 together with that for [FORMULA] Mpc. The features in [FORMULA] come from the mentioned structure in its rotation curve. The predicted MOND rotation curve is drawn in Fig. 4 for the latter distance and [FORMULA]. It is seen that the MOND rotation curve does not reproduce the detailed rotation curve if one requires the existence of a stable disc. For higher [FORMULA] the predicted curve becomes completely smoothed. Roughly, the same discussion on the concerns of decreasing the distance given in Sect. 3.2 holds for NGC 1560.

[FIGURE] Fig. 3. The Toomre parameter for the gaseous disc of NGC 1560 at D = 3.0 Mpc (solid line) and at D = 2.25 Mpc (dashed line). A value of [FORMULA] km/s was assumed.

[FIGURE] Fig. 4. The predicted MOND rotation curve of NGC 1560 at D = 2.25 Mpc and [FORMULA].

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© European Southern Observatory (ESO) 1999

Online publication: April 12, 1999