Bibcode
Knapen, J. H.; Beckman, J. E.
Bibliographical reference
Monthly Notices of the Royal Astronomical Society, Vol. Vol. 283, No. 1, p. 251 - 262
Advertised on:
11
1996
Citations
39
Refereed citations
34
Description
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 Hα, H I 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. H I is formed near the young massive stars as a result of
photodissociation. From radial profiles we find that in the region of
the star-forming spiral arms the exponential scalelengths for Hα,
blue and near-infrared light, and 21-cm radio continuum are equal within
the fitting errors. The scalelengths for the interarm region are also
equal for all these tracers, but the arm scalelengths 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 scalelengths are
equivalent to an outwardly increasing arm-interarm contrast. We argue
that the radial profiles of radio continuum and H I, 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 inside 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 quantity of interstellar dust, controlling
the equilibrium between the molecular and atomic form of hydrogen. Over
most of the inner part of the disc, H I seems to be a product of the
star formation processes rather than the cause of enhanced star
formation.