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The Small Magellanic Cloud: A Template for the Primitive
Interstellar Medium
The Small Magellanic Cloud (SMC) --- with its unobscured
line of sight, its small internal extinction, and its profusion
of star-forming sites --- constitutes an excellent laboratory
to study the interaction between massive stars, molecular
clouds, and their environment. As a gas-rich, irregular galaxy
with low heavy-element abundances and an intense UV interstellar
radiation field stemming from active star formation, the SMC
is a window that allows us to probe the properties of the
interstellar medium (ISM) in primordial galaxies at high redshifts.
Indeed, recent studies of UV attenuation by internal dust
in Lyman break galaxies find them more similar in their dust
properties to the SMC than to the Milky Way (Vijh et al. 2003).
Last year we were granted 50 hours of Spitzer's observing
time to image the entire SMC with IRAC and MIPS in all their
bands, a feat that is only possible due to Spitzer's unprecedented
sensitivity. These observations will allow us, for the first
time, to quantify the distribution and properties of very
small grains (VSGs) and polycyclic aromatic hydrocarbons (PAHs)
across the SMC. These data, when combined with MIPS observations
and the existing ground-based HI, CO, centimeter and millimeter
continuum, optical, and near infrared observations, will enable
us to study the properties and distribution of the interstellar
dust in relation to their interstellar environment. Furthermore,
the sensitivity of the proposed observations is enough to
detect OB and AGB stars to a high level of significance in
the shortest IRAC wavebands. Thus, it will allow us to obtain
for the first time a complete census of the massive star formation
activity and evolved stellar content in this galaxy, regardless
of obscuration.
Goals of this project
VSGs and PAHs play a crucial role in the heating and cooling
balance in the ISM, yet very little is known about their properties,
distribution, and life-cycle. The purpose of this project
is to obtain --- for the first time --- a complete image of
the SMC in the midIR and FIR wavebands, using IRAC and MIPS.
The area mapped encompasses the bulk of the star formation,
FIR emission. Information in all wavebands is necessary to
disentangle the effects of PAH emission, midIR continuum,
and grain size and temperature on the SED. We will use these
data to address the following scientific questions:
(i) What is the abundance and distribution of VSGs and PAHs
in the SMC?
(ii) Testing and constraining the current dust models
(iii) Census of star formation in the SMC
(iv) Distribution of small and large grains across the SMC.
Hidden molecular gas?
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