Testing the dark matter origin of the WMAP-Planck Haze with radio
  observations of Spiral Galaxies
  If the Galactic WMAP radio haze, as recently confirmed by Planck, is produced
by dark matter annihilation or decay, similar diffuse radio halos should exist
around other galaxies with physical properties comparable to the Milky Way. If
instead the haze is due to an astrophysical mechanism peculiar to the Milky Way
or to a transient event, a similar halo need not exist around all Milky Way
"twins". We use radio observations of 66 spiral galaxies to test the dark
matter origin of the haze. We select galaxies based on morphological type and
maximal rotational velocity, and obtain their luminosities from a 1.49 GHz
catalog and additional radio observations at other frequencies. We find many
instances of galaxies with radio emission that is less than 5% as bright as
naively expected from dark matter models that could produce the Milky Way haze,
and at least 3 galaxies that are less than 1% as bright as expected, assuming
dark matter distributions, magnetic fields, and cosmic ray propagation
parameters equal to those of the Milky Way. For reasonable ranges for the
variation of these parameters, we estimate the fraction of galaxies that should
be expected to be significantly less bright in radio, and argue that this is
marginally compatible with the observed distribution. While our findings
therefore cannot rule out a dark matter origin for the radio haze at this time,
we find numerous examples (including the Andromeda Galaxy) where, if dark
matter is indeed the origin of the Milky Way haze, some mechanism must be in
place to suppress the corresponding haze of the external galaxy. We point out
that Planck data will offer opportunities to improve this type of constraint in
a highly relevant frequency range and for a potentially larger set of candidate
galaxies.
