We examine the amplitude of the rotation velocity that can be attributed to the dark matter halos of disk galaxies , focusing on well measured intermediate radii .
The data for 60 galaxies spanning a large range of mass and Hubble types , taken together , are consistent with a dark halo velocity \log V _ { h } = \mathfrak { C } + \mathfrak { B } \log r with \mathfrak { C } = 1.47 ^ { +0.15 } _ { -0.19 } and \mathfrak { B } \approx \text@frac { 1 } { 2 } over the range 1 < r < 74 kpc .
The range in \mathfrak { C } stems from different choices of the stellar mass estimator , from minimum to maximum disk .
For all plausible choices of stellar mass , the implied densities of the dark halos are lower than expected from structure formation simulations in \Lambda CDM , which anticipate \mathfrak { C } > 1.6 .
This problem is not specific to a particular type of galaxy or to the innermost region of the halo ( cusp or core ) ; the velocity attributable to dark matter is too low at all radii .