/L) concept.
But this is a very crude approximation at best. Since edge-on observations of disk galaxies reveal a darker edge against a brighter bulge background, it is clear that M/L concepts do not apply to disk galaxies.
(6) To compensate for the inconsistencies encountered with above approaches (3) and (4), other authors unjustifiably assume Dark Matter exists in Spherical Distributions, which leads to the untenable speculation re Massive Peripheral Spherical Halos of Mysterious Dark Matter around Rotating Disk Galaxies. It would be more appropriate to assume that any Dark Matter exists within the disk, and then discover that there is slightly more ordinary matter towards the cooler/darker periphery, consistent with our analyses (references below).
The persistent penchant for cosmologists to speculate re Dark Mysteries is UNscientific, and worsened by unjustified claims of “undeniability” contrary to experiments, observations and experimentally established physics.
But alternative perspectives are available in the literature as follows.
For example, in our approach (references below), we assume Newtonian gravity and dynamics applied to a rotating thin-disk galaxy of finite radial dimensions.
We balance the gravitational and centrifugal forces at each and every point on the rotating disk, and use the galactic rotational data (radially dependent) as input, and solve for the consistent radial mass distribution.
Our radial mass distributions do not differ drastically from the M/L ratio, but we find more mass towards the galactic periphery which is cooler/darker consistent with the darker edge-on observations. And we deduce total galactic masses consistent with star counts, a critical additional confirmation of the validity of our approach and results.
“Modeling the Newtonian Dynamics for Rotation Curve Analysis of Thin-Disk Galaxies,” By Feng and Gallo, Research in Astronomy and Astrophysics 11 (2011) 1429-1448. www.raa-journal.org. http://arxiv.org/abs/1104.3236
“A Thin-Disk Gravitational Model for Galactic Rotation,” by Gallo and Feng, Astronomical Society of Pacific Conference Proceedings, vol 413, p 289-303, Dec 2009, CCC2 Conference in Port Angeles, Sept 2008.
“Galactic Rotation Described by a Thin-Disk Gravitational Model Without Dark Matter,” C. F. Gallo and James Q. Feng, Journal of Cosmology, April 2010, Vol 6, 1373-1380. http://journalofcosmology.com/Contents6.html Paper #4.