First measurement of the bulk flow of nearby galaxies using the cosmic
  microwave background
  Peculiar velocities in the nearby Universe can be measured via the kinetic
Sunyaev-Zel'dovich (kSZ) effect. Using a statistical method based on an
optimised cross-correlation with nearby galaxies, we extract the kSZ signal
generated by plasma halo of galaxies from the Cosmic Microwave Background (CMB)
temperature anisotropies observed by the Wilkinson Microwave Anisotropy Probe
(WMAP). Marginalising over the thermal Sunyaev-Zel'dovich contribution from
clusters of galaxies, possible unresolved point source contamination, and
Galactic foregrounds (dust, synchrotron and free-free emission), we report a
kSZ bulk flow signal present at the 90% confidence level in the seven-year WMAP
data. When only galaxies within 50 Mpc/h are included in the kSZ template we
find a bulk flow in the CMB frame of |V|=533 +/- 263 km/s, in the direction
l=324 +/- 27, b=-7 +/- 17, consistent with bulk flow measurements on a similar
scale using classical distance indicators. We show how this comparison
constrains the (ionised) baryonic budget in the local universe. On very large
(~ 500 Mpc/h) scales, we find a 95% upper limit of 470 km/s, inconsistent with
some analyses of bulk flow of clusters from the kSZ. We estimate that the
significance of the bulk flow signal may increase to 3-5 sigma using data from
the PLANCK probe.
