Herschel far-infrared observations of the Carina Nebula complex I:
  Introduction and global cloud structure
  The Carina Nebula represents one of the most massive galactic star forming
regions and displays a high level of massive star feedback. We used SPIRE and
PACS onboard of Herschel to map the full spatial extent of the clouds in the
Carina Nebula complex at wavelengths between 70 and 500 micrometer. We
determine color temperatures and column densities of the clouds in the complex.
Our Herschel maps show that the clouds have a very complex and filamentary
structure that is dominated by the radiation and wind feedback from the massive
stars. In most locations, the column density of the clouds is N_H < 2x10^22
cm^-2; denser cloud structures are restricted to just a few locations. We find
a clear large scale temperature gradient from 35-40 K in the central region to
<20 K at the periphery and in the densest parts of individual pillars. The
total mass of the clouds seen by Herschel in the central (1 deg radius) region
is ~656000 M_sun. A simple radiative transfer model for the global spectral
energy distribution suggests that the total mass of all the gas (including a
warmer component that is not well traced by Herschel) is <=890000 M_sun.
Despite the strong feedback from numerous massive stars that is going on since
several million years, there are still several 10000 M_sun of cool cloud
material present at column-densities sufficient for further star formation.
Comparison of our total gas mass estimates to molecular cloud masses derived
from CO line mapping suggests that as much as about 75% of all the gas is in
atomic rather than molecular form.
