Heating up the Galaxy with Hidden Photons
  We elaborate on the dynamics of ionized interstellar medium in the presence
of hidden photon dark matter. Our main focus is the ultra-light regime, where
the hidden photon mass is smaller than the plasma frequency in the Milky Way.
We point out that as a result of the Galactic plasma shielding direct detection
of ultra-light photons in this mass range is especially challenging. However,
we demonstrate that ultra-light hidden photon dark matter provides a powerful
heating source for the ionized interstellar medium. This results in a strong
bound on the kinetic mixing between hidden and regular photons all the way down
to the hidden photon masses of order $10^{-20}$ eV.
