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==> In this proposal, more time is being requested for FCOMBES.M31_SPI2
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Because of its proximity (690kpc), the Andromeda galaxy is a
unique opportunity to study the distribution of FIR emission
lines in a spiral galaxy: it is the only density-wave galaxy
where spiral arms are resolved by ISO (M33 being more stochastic).
Physical conditions (excitation, temperature and density), as
well as the spectral type of exciting stars, can be determined,
as a function of location with respect to spiral arms, or main
active regions. Observations of the Milky Way cannot give this
global structure across an arm due to our unfavored location in
the plane of the galaxy.
A wealth of data are available already on M31, allowing fruitful
comparisons with tracers of star formation: cold and dense gas
through CO maps, atomic and more diffuse gas at 21cm, ionised
gas (Halpha), UV and FIR tracing young stars. The CII map will
bring new and complementary information in that it is free of
extinction, and can probe the star-formation deep into molecular
clouds (contrary to UV and Halpha); since it is the main coolant
of excited regions, and the product of CO photodissociation,
it will trace the precise locations of star-formation activity
(and complement IRAS data). We will then determine the role of
spiral arms and in general large-scale trigger in star-formation.