They go on to say, in the conclusions, that:
Quote:
There is no need for non-baryonic dark matter in galaxies NGC 4736 or NGC 7793, but one cannot conclude that one does not need it in other spiral galaxies.
NGC 6946 is not so clear. There are significant discrepancies between published rotation curves, and consequently, in the obtained Mass/Light (M/L) ratios.
Galaxy UGC 6446 satisfies some of our criteria without non-baryonic dark matter, however its M/L ratio is highest and, in addition, it grows dramatically toward galaxy "edge".
There is a strong argument for absence of spherical non-baryonic dark halo. This argument does not exclude the presence of a non-spherical halo. However, the mass needed in the galaxy outskirts to account for the rotation in the disk model is practically that of gas. It would be therefore worthwhile to consider other than CDM causes of the M/L ratio growth.
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So, in other words;
- some Galaxies don't need any Cold Dark Matter (CDM) to explain their RCs;
- different amounts of CDM needed to explain some Galaxies' RCs;
- different models are needed to explain other Galaxies' RCs.
Not as straightforward as the commonly heard saying: 'flat rotation curves in galaxies means Dark Matter is required to explain them'.
Cheers