Bending Waves in Velocity Space: a First Look at the THINGS sample
  Detection of bending waves is a highly challenging task even in nearby disc
galaxies due to their sub-kpc bending amplitudes. However, simulations show
that the harmonic bending of a Milky Way like disc galaxy is associated with a
harmonic fluctuation in the measured line of sight (los) velocities as well,
and can be regarded as a kinematic signature of a manifested bending wave.
Here, we look for similar kinematic signatures of bending waves in \HI discs,
as they extend to much beyond the optical radii.
  We present a multipole analysis of the \HI los residual velocity fields of
six nearby spiral galaxies from the THINGS sample, which uncovers the bending
wave-induced velocity peaks. This allows us to identify the radial positions
and amplitudes of the different bending modes present in the galaxies. We find
that all of our sample discs show a combined kinematic signature of
superposition of a few lower-order bending modes, suggesting that bending waves
are a common phenomenon. The identified velocity peaks are found to be of modes
$m=2,3$ and $4$, not more than 15 km s$^{-1}$ in amplitude and spread across
the entire \HI disc. Interestingly, they appear to be concentrated near the
optical edge of their host galaxies. Also, $m=2$ appears to be more common than
the other two modes.
