Turbulent universal galactic Kolmogorov velocity cascade over 6 decades
  We report the evidence for the existence of the universal, continuous
turbulent cascade of velocity fluctuations with Kolmogorov -5/3 slope spanning
6 orders of length scales, from $10^4$ pc down to $10^{-2}$ pc. This was
achieved by applying our innovative technique of separating density and
velocity fluctuations to a set of spectroscopic surveys featuring various
galactic spectral lines. This unified velocity cascade involves different
interstellar phases from diffuse galactic media to dense self-gravitating
clouds and persists despite interstellar phase transitions. However, the
turbulent density fluctuations do not show this universality as the value of
the spectral slope changes in different interstellar phases. This agrees with
the expectation of compressible turbulence theory and demonstrates that the
density is only an indirect tracer of interstellar turbulence. We report that
the density fluctuations for clouds and filaments that are preferentially
parallel to magnetic fields exhibit the spectral slope of -2. The universal
grand turbulent velocity cascade that is established in our paper has
significant implications for key galactic physical processes, including star
formation, cosmic ray transport etc. We anticipate our result to be a starting
point for in vitro models of multiphase interstellar turbulence studies with a
significant impact for modeling of spiral galaxies.
