Figure 3: The Baryonic Tully–Fisher (mass–rotation velocity) relation for galaxies with
well-measured outer velocities . The baryonic mass is the combination of observed stars and gas:
. Galaxies have been selected that have well observed, extended rotation curves from
21 cm interferrometric observations providing a good measure of the outer, flat rotation velocity. The
dark blue points are galaxies with [272]. The light blue points have [276]
and are generally less precise in velocity, but more accurate in terms of the harmlessness on the
result of possible systematics on the stellar mass-to-light ratio. For a detailed discussion of the stellar
mass-to-light ratios used here, see [272, 276]. The dotted line has slope 4 corresponding to a constant
acceleration parameter, . The dashed line has slope 3 as expected in CDM
with the normalization expected if all of the baryons associated with dark matter halos are detected.
The difference between these two lines is the origin of the variation in the detected baryon fraction
in Figure 2.
|