zoki85 said:
Why should BDM be so substantional in the disk and not in the center of galaxy is even bigger riddle than nature of Dark matter.
I can't give you a precise quantitative answer, but in these disk models, the density of all baryonic matter falls off fairly rapidly from the center of the galaxy. Very little of the central mass is dark. There is lots of stellar radiation that warms the H2 clouds, plasma and dust in the visible disk. However, galactic disks extend far beyond the luminous part (which contains almost all of the visible stars). We already know this from the distribution of HI. The main unknown is how much additional matter exists far from the center that we cannot detect. While the overall density drops rapidly, the suggestion is that there may be more outer BDM than generally assumed. The mass distribution argument is mainly that the M/L ratio increases with distance, even though the total density decreases with distant.
There is no riddle here. As you get farther from the center luminosity declines. This indicates that the density at some distance is too low to form stars. However, it is not reasonable (and in fact wrong) to conclude that no mass exist outside this radius just because no stars are formed.
Here are some papers that address rotation curves of disk galaxies using baryonic matter only and standard Newtonian gravity:
http://arxiv.org/abs/1408.5054 Deficient Reasoning for Dark Matter in Galaxies (The tone of this paper seems to reflect frustration. The authors have published many related papers in the past.)
http://arxiv.org/abs/1011.1538 Galactic rotation curves inspired by a noncommutative-geometry background [this is about stability without DM halos]
http://arxiv.org/abs/1104.3236 Modeling the Newtonian dynamics for rotation curve analysis of thin-disk galaxies
http://arxiv.org/abs/1007.3778 Rotating thin-disk galaxies through the eyes of Newton
http://arxiv.org/abs/0906.4448 Global disc models for galaxies NGC 1365, 6946, 7793 and UGC 6446
http://arxiv.org/abs/0902.1703 The mass distribution in Spiral galaxies
http://arxiv.org/abs/0809.3135 On the axisymmetric thin disc model of flattened galaxies
http://arxiv.org/abs/0806.1131 Newtonian mechanics & gravity fully model disk galaxy rotation curves without dark matter
http://arxiv.org/abs/astro-ph/0309823 Errors in equations for galaxy rotation speeds
http://arxiv.org/abs/astro-ph/0309762 Galactic mass distribution without dark matter or modified Newtonian mechanics
http://arxiv.org/abs/astro-ph/0611113 Is Dark Matter Present in NGC 4736? An Iterative Spectral Method for Finding Mass Distribution in Spiral Galaxies
A common first order mistake is to assume that there
should be Keplerian orbital speeds and that therefore we need lots of dark matter. This stems the incorrect assumption that all galactic matter closer to the center can be treated as a point mass or a uniform spherical mass and similarly that matter farther from the center can be ignored when computing the rotational velocity of a star. Both assumptions are wrong because the distribution in disk galaxies is flat rather than spherical. The situation is entirely different from the solar system where 99% of the matter is concentrated in the sun.
Computing the expected rotation curve from the mass distribution is not trivial. Some attempts have failed due to complications in the approach used. Other authors have succeeded in deriving analytic solutions and others have written numerical programs. In the later case, it is possible to begin with a known rotation curve and work backwards to compute a corresponding disk mass distribution.