Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Global morphology and physical relations between the stars, gas and dust
  in the disc and arms of M100   We study star formation processes in the disc of the weakly barred grand
design spiral galaxy M100 (NGC 4321) from a variety of images tracing recent
massive star formation, old and young stars, dust, and neutral hydrogen.
Differences between arm and interarm regions are specifically studied by
decomposing the images into arm and non-arm zones. We find from a comparison of
the morphology in H$\alpha$, HI and dust that while the first two are
coincident over most of the disc, they are offset from the dust lanes
especially along the inner parts of the spiral arms: a picture which is
indicative of a density wave shock moving through the arms. HI is formed near
the young massive stars as a result of photo-dissociation. From radial profiles
we find that in the region of the star-forming spiral arms the exponential
scale lengths for H$\alpha$, blue and near-infrared light, and 21 cm radio
continuum are equal within the fitting errors. The scale lengths for the
interarm region are also equal for all these tracers, but the arm scale lengths
are significantly longer. This points to a common origin of the profiles in
star formation, with little or no influence from radial population gradients or
dust in the disc of this galaxy. The longer arm scale lengths are equivalent to
an outwardly increasing arm-interarm contrast. We argue that the radial
profiles of radio continuum and HI, as well as CO, are also directly regulated
by star formation, and discuss the possible implications of this result for the
interpretation of observed CO intensities in and outside spiral arms. We
discuss the radial atomic hydrogen profile in some detail. Its almost perfectly
flat shape in the region of the star-forming spiral arms may be explained by
photodissociation and recombination processes in the presence of a limited

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The categories of this paper are: nucl-ex
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The categories of this paper are: q-bio
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The categories of this paper are: stat
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The categories of this paper are: comp-gas
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The categories of this paper are: nlin
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The categories of this paper are: q-alg
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The categories of this paper are: math
32
The categories of this paper are: atom-ph
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The categories of this paper are: solv-int
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The categories of this paper are: cmp-lg
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The categories of this paper are: hep-th
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The categories of this paper are: hep-ex
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The categories of this paper are: dg-ga
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The categories of this paper are: acc-phys
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The categories of this paper are: cond-mat
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The categories of this paper are: nucl-th