Planck early results. XXI. Properties of the interstellar medium in the
  Galactic plane
  (abridged) Planck has observed the entire sky from 30 GHz to 857GHz. The
observed foreground emission contains contributions from different phases of
the interstellar medium (ISM). We have separated the observed Galactic emission
into the different gaseous components (atomic, molecular and ionised) in each
of a number of Galactocentric rings. Templates are created for various
Galactocentric radii using velocity information from atomic (neutral hydrogen)
and molecular (12CO) observations. The ionised template is assumed to be traced
by free-free emission as observed by WMAP, while 408 MHz emission is used to
trace the synchrotron component. Gas emission not traced by the above
templates, namely "ark gas", as evidenced using Planck data, is included as an
additional template, the first time such a component has been used in this way.
These templates are then correlated with each of the Planck frequency bands, as
well as other ancillary data. The emission per column density of the gas
templates allows us to create distinct spectral energy distributions (SEDs) per
Galactocentric ring and in each of the gaseous tracers from 1.4 GHz to 25 THz
(12\mu m). Apart from the thermal dust and free-free emission, we have probed
the Galaxy for anomalous (e.g., spinning) dust as well as synchrotron emission.
We show that anomalous dust emission is present in the atomic, molecular and
dark gas phases throughout the Galactic disk. The derived dust propeties
associated with the dark gas phase are derived but do not allow us to reveal
the nature of this phase. For all environments, the anomalous emission is
consistent with rotation from polycyclic aromatic hydrocarbons (PAHs) and,
according to our simple model, accounts for $(25\pm5)%$ (statistical) of the
total emission at 30 GHz.
