A Spitzer Space Telescope survey of massive young stellar objects in the
  G333.2-0.4 giant molecular cloud
  The G333 giant molecular cloud contains a few star clusters and H II regions,
plus a number of condensations currently forming stars. We have mapped 13 of
these sources with the appearance of young stellar objects (YSOs) with the
Spitzer Infrared Spectrograph in the SL, SH, and LH modules (5-36 micron). We
use these spectra plus available photometry and images to characterize the
YSOs. The spectral energy distributions (SEDs) of all sources peak between 35
and 110 micron, thereby showing their young age. The objects are divided into
two groups: YSOs associated with extended emission in IRAC band 2 at 4.5 micron
(`outflow sources') and YSOs that have extended emission in all IRAC bands
peaking at the longest wavelengths (`red sources'). The two groups of objects
have distinctly different spectra: All the YSOs associated with outflows show
evidence of massive envelopes surrounding the protostar because the spectra
show deep silicate absorption features and absorption by ices at 6.0, 6.8, and
15.2 micron. We identify these YSOs with massive envelopes cool enough to
contain ice-coated grains as the `bloated' protostars in the models of Hosokawa
et al. All spectral maps show ionized forbidden lines and PAH emission
features. For four of the red sources, these lines are concentrated to the
centres of the maps, from which we infer that these YSOs are the source of
ionizing photons. Both types of objects show evidence of shocks, with most of
the outflow sources showing a line of [S I] in the outflows and two of the red
sources showing the more highly excited [Ne III] and [S IV] lines in outflow
regions at some distance from the YSOs. The 4.5 micron emission seen in the
IRAC band 2 images of the outflow sources is not due to H2 lines, which are too
faint in the 5-10 micron wavelength region to be as strong as is needed to
account for the IRAC band 2 emission.
