Constraining physical conditions for the PDR of Trumpler 14 in the
  Carina Nebula
  We investigate the physical conditions of the CO gas near the young star
cluster, Trumpler 14 of the Carina Nebula. The observations presented in this
work are taken with the Fourier Transform Spectrometer (FTS) of the Spectral
and Photometric Imaging REceiver (SPIRE) onboard the Herschel Space
Observatory. Our field of view covers the edge of a cavity carved by Trumpler
14 about $1\,\mathrm{Myr}$ ago and marks the transition from HII regions to
photo-dissociation regions. With the state-of-the-art Meudon PDR code, we
successfully derive the physical conditions, which include the thermal pressure
($P$) and the scaling factor of radiation fields ($G_{\mathrm{UV}}$), from the
observed CO spectral line energy distributions~(SLEDs) in the observed region.
The derived $G_{\mathrm{UV}}$ values generally show an excellent agreement with
the UV radiation fields created by nearby OB-stars and thus confirm that the
main excitation source of the observed CO emission are the UV-photons provided
by the massive stars. The derived thermal pressure is between
$0.5-3\,\times\,10^{8}\,\mathrm{K\,cm^{-3}}$ with the highest values found
along the ionization front in Car I-E region facing Trumpler 14, hinting that
the cloud structure is similar to the recent observations of the Orion Bar.
Comparing the derived thermal pressure with the radiation fields, we report the
first observationally-derived and spatially-resolved $P \sim
2\times10^4\,G_{\mathrm{UV}}$ relationship. As direct comparisons of the
modeling results to the observed $^{13}\mathrm{CO}$, [OI] $63\,\mathrm{\mu m}$,
and [CII] $158\,\mathrm{\mu m}$ intensities are not straightforward, we urge
the readers to be cautious when constraining the physical conditions of PDRs
with combinations of $^{12}\mathrm{CO}$, $^{13}\mathrm{CO}$, [CI], [OI]
$63\,\mathrm{\mu m}$, and [CII] $158\,\mathrm{\mu m}$ observations.
