The physical properties of the dust in the RCW 120 HII region as seen by
  Herschel
  Context. RCW 120 is a well-studied, nearby Galactic HII region with ongoing
star formation in its surroundings. Previous work has shown that it displays a
bubble morphology at mid-infrared wavelengths and has a massive layer of
collected neutral material seen at sub-mm wavelengths. Given the well-defined
photo-dissociation region (PDR) boundary and collected layer, it is an
excellent laboratory to study the "collect and collapse" process of triggered
star formation. Using Herschel Space Observatory data at 100, 160, 250, 350,
and 500 micron, in combination with Spitzer and APEX-LABOCA data, we can for
the first time map the entire spectral energy distribution of an HII region at
high angular resolution. Aims. We seek a better understanding of RCW120 and its
local environment by analysing its dust temperature distribution. Additionally,
we wish to understand how the dust emissivity index, beta, is related to the
dust temperature. Methods. We determine dust temperatures in selected regions
of the RCW 120 field by fitting their spectral energy distribution (SED),
derived using aperture photometry. Additionally, we fit the SED extracted from
a grid of positions to create a temperature map. Results. We find a gradient in
dust temperature, ranging from >30 K in the interior of RCW 120, to ~20K for
the material collected in the PDR, to ~10K toward local infrared dark clouds
and cold filaments. Our results suggest that RCW 120 is in the process of
destroying the PDR delineating its bubble morphology. The leaked radiation from
its interior may influence the creation of the next generation of stars. We
find support for an anti-correlation between the fitted temperature and beta,
in rough agreement with what has been found previously. The extended wavelength
coverage of the Herschel data greatly increases the reliability of this result.
