Aims. Most studies of high-mass star formation focus on massive and/or luminous clumps, but the physical properties of their larger scale environment are poorly known. In this work, we aim at characterising the effects of clustered star formation and feedback of massive stars on the surrounding medium by studying the distribution of warm gas through mid-J (CO)-C-12 and (CO)-C-13 observations.
Methods. We present APEX (CO)-C-12(6-5), (7-6), (CO)-C-13(6-5), (8-7) and HIFI (CO)-C-13(10-9) maps of the star forming region G327.36-0.6 with a linear size of similar to 3 pc x 4 pc. We infer the physical properties of the emitting gas on large scales through a local thermodynamic equilibrium analysis, while we apply a more sophisticated large velocity gradient approach on selected positions.
Results. Maps of all lines are dominated in intensity by the photon dominated region around the HII region G327.3-0.5. Mid-J (CO)-C-12 emission is detected over the whole extent of the maps with excitation temperatures ranging from 20 K up to 80 K in the gas around the HII region, and H-2 column densities from few 10(21) cm(-2) in the inter-clump gas to 3 x 10(22) cm(-2) towards the hot core G327.3-0.6. The warm gas (traced by (12) and (CO)-C-13(6-5) emission) is only a small percentage (similar to 10%) of the total gas in the infrared dark cloud, while it reaches values up to similar to 35% of the total gas in the ring surrounding the HII region. The (CO)-C-12 ladders are qualitatively compatible with photon dominated region models for high density gas, but the much weaker than predicted (CO)-C-13 emission suggests that it comes from a large number of clumps along the line of sight. All lines are detected in the inter-clump gas when averaged over a large region with an equivalent radius of 50 '' (similar to 0.8 pc), implying that the mid-J (CO)-C-12 and (CO)-C-13 inter-clump emission is due to high density components with low filling factor. Finally, the detection of the (CO)-C-13(10-9) line allows to disentangle the effects of gas temperature and gas density on the CO emission, which are degenerate in the APEX observations alone.
- stars: formation
- HII regions
- ISM: individual objects: G327.3-0.6
- HOT CORE G327.3-0.6
- HERSCHEL-SPIRE SPECTROSCOPY
- YOUNG STELLAR OBJECTS
- MOLECULAR CLOUD CORE
- H II REGIONS
- LINE EMISSION