Confronting Cold Dark Matter Predictions with Observed Galaxy Rotations
  The rich statistics of galaxy rotations as captured by the velocity function
(VF) provides invaluable constraints on galactic baryon physics and the nature
of dark matter (DM). However, the comparison of observed galaxy rotations
against cosmological models is prone to subtle caveats that can easily lead to
misinterpretations. Our analysis reveals full statistical consistency between
~5000 galaxy rotations, observed in line-of-sight projection, and predictions
based on the standard cosmological model (LCDM) at the mass-resolution of the
Millennium simulation (HI line-based circular velocities above ~50 km/s).
Explicitly, the HI linewidths in the HI Parkes All Sky Survey (HIPASS) are
found consistent with those in S3-SAX, a post-processed semi-analytic model for
the Millennium simulation. Previously found anomalies in the VF can be
plausibly attributed to (1) the mass-limit of the Millennium simulation, (2)
confused sources in HIPASS, (3) inaccurate inclination measurements for
optically faint sources, and (4) the non-detectability of gas-poor early-type
galaxies. These issues can be bypassed by comparing observations and models
using linewidth source counts rather than VFs. We investigate if and how well
such source counts can constrain the temperature of DM.
