Planck 2013 results. XIII. Galactic CO emission
  Rotational transition lines of CO play a major role in molecular radio
astronomy and in particular in the study of star formation and the Galactic
structure. Although a wealth of data exists in the Galactic plane and some
well-known molecular clouds, there is no available CO high sensitivity all-sky
survey to date.
  Such all-sky surveys can be constructed using the \Planck\ HFI data because
the three lowest CO rotational transition lines at 115, 230 and 345 GHz
significantly contribute to the signal of the 100, 217 and 353 GHz HFI channels
respectively. Two different component separation methods are used to extract
the CO maps from Planck HFI data. The maps obtained are then compared to one
another and to existing external CO surveys. From these quality checks the best
CO maps in terms of signal to noise and/or residual foreground contamination
are selected. Three sets of velocity-integrated CO emission maps are produced:
Type 1 maps of the CO (1-0), (2-1), and (3-2) rotational transitions with low
foreground contamination but moderate signal-to-noise ratio; Type 2 maps for
the (1-0) and (2-1) transitions with a better signal-to-noise ratio; and one
Type 3 map, a line composite map with the best signal-to-noise ratio in order
to locate the faintest molecular regions. The maps are described in detail.
They are shown to be fully compatible with previous surveys of parts of the
Galactic Plane and also of fainter regions out of the Galactic plane. The
Planck HFI velocity-integrated CO maps for the (1-0), (2-1), and (3-2)
rotational transitions provide an unprecedented all-sky CO view of the Galaxy.
These maps are also of great interest to monitor potential CO contamination on
CMB \Planck\ studies.
