Galactic rotation curve

The existence of dark matter (either baryonic or non-baryonic) is inferred from its gravitational effects on galactic rotation curves, the velocity dispersions and hydrostatic equilibrium of hot (X-ray) gas in clusters and groups of galaxies, gravitational lensing and departures from the smooth Hubble flow described by Eq. (4.1). This dark matter resides at least partly in the halos of galaxies such as our... 

We present chemical evolution models for NGC 6822 computed with five fixed parameters, all constrained by observations, and only a free parameter, related with galactic winds. The fixed parameters are i) the infall history that has produced NGC 6822 is derived from its rotation curve and a cosmological model ii) the star formation history of the whole galaxy based on star formation histories for 8 zones inferred from H-R diagrams iii) the IMF, the stellar yields, and the percentage of Type la SNe progenitors are the same than those that reproduce the chemical history of the Solar Vicinity and the Galactic disk. 

Fig. 8.14. Surface densities of atomic and molecular hydrogen in the Galaxy as a function of Galactocentric distance the Sun is at 8.5 kpc. Beyond that distance, the deduced surface density depends on the assumed law of Galactic rotation KBH refers to Kulkarni, Blitz and Heiles (1982). Assuming their rotation curve, the total gas surface density falls by about a factor of 2 between 4.5 and 13 kpc, corresponding to an exponential fall-off with a scale length a l of about 12 kpc. After Dame (1993). Courtesy T.M. Dame.

Note that the baryonic density of 2% to 5% is of the same order of magnitude as the galactic density indicated by rotation curves (viz. 5%). It is thus perfectly reasonable to suggest that a large part of galactic matter is located in compact massive objects (CMOs) assumed to swarm around the bright galactic disk. Will these compact massive objects remain forever hidden ... 

---