| dc.description.abstract | Massive star formation takes place in the dense cores of molecular clouds where the
stars may be obscured at optical wavelengths. An excellent signpost of a massive
young stellar object is the presence of an ultra-compact HII region (UCHii), which
is a dense photo-ionised cocoon of gas surrounding the newly formed star. The aim
of this project is to develop an assembly of numerical tools, caravela, that can simulate
realistic data streams representing high-mass star forming regions in our Galaxy.
The synthetic output consists in images and photometric point source catalogues,
in the IRAS and Herschel wavebands. In an era when large observational surveys
are increasingly important, this tool can produce simulated infrared point-source
catalogues of high-mass star forming regions on a Galactic scale. The approach
used is to construct a synthetic Galaxy of star-forming regions represented by SED
templates. The star-forming regions are distributed randomly along a four spiral
arm morphology, although a wide range of geometries can be used including rings
and different numbers of spiral arms. The caravela code then observes the synthetic
Galaxy to produce simulated images and point source catalogues with appropriate
sensitivity and angular resolution. caravela was first used to model the simulated
Galaxy by constraining the synthetic output to observations made by IRAS. This
numerical tool will allow the user to infer physical properties of the Galactic population
of high-mass star forming regions from such observations. Second, the selected
model was again observed with caravela in Herschel mode. These are therefore predictive
results for the future Herschel observations. A model with 4.0×104 compact
proto-stars embedded in larger grey-body envelopes (with T = 40 K and linear size
scale lIII = 5.0 × 106 AU) is the best-fit model to the IRAS observational data set
studied. We found a level of contamination from low- and intermediate-mass objects
of " 90%. The modelled data set resulting from the Herschel simulation resulted
in the detection of approximately twice as many Herschel objects than IRAS, which
is consistent, in a limited way, with the real observed companion clump fraction
(CCF) of 0.90 ± 0.07 (Thompson et al., 2006) means that on average there were
observed 2 sources per one IRAS source. Our caravela and the real observed CCF
are therefore consistent. caravela was coupled with an independent diffuse emission
model (Paladini et al., 2007) and the resulting analysis is presented as an interesting
seed for the future. | en_US |
