Bibcode
Cepa, J.; Beckman, J. E.; Knapen, J. H.
Bibliographical reference
In NASA. Ames Research Center, The Evolution of Galaxies and Their Environment p 233-234 (SEE N93-26706 10-90)
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1
1993
Citations
0
Refereed citations
0
Description
In normal spiral galaxies the arms are the main sites for star
formation. This is the cause of their optical contrast compared with the
rest of the disc. The spiral structure can be observed as a higher
concentration of H2 regions, neutral gas (both atomic and molecular via
CO), dust and stars than in the interarm disc. It seens generally
accepted that, at least in grand design spirals, there are density waves
in the discs. However, several questions are not clear yet and still
under discussion. An important question could be termed the triggering
dilemma (by analogy with the 'winding dilemma' raised in the forties):
Is the enhanced star formation in the spiral arms triggered by the
passage of a system of density waves or is it simply due to the presence
of a higher column density of gas there? In the present work, we use
triggering in the same sense as the moderate to strong triggering
defined by Elmegreen (1992), that is to say that star formation in the
arms occurs at a rate faster than that in the interarm zone, relative to
the available placental gas. Our group has designed several tests to
elucidate whether or not star formation is triggered in the arms with
respect to the interarm region and we summarize one of them, that of the
ratio of the star formation efficiency in the arms divided by that of
the interarm zone at the same galactocentric distance which we may call
the relative massive star formation efficiency, where the efficiency is
defined using the ratio of the mass of stars (evaluated via the H alpha
flux) to the mass of neutral gas, atomic plus molecular (which must be
measured with the adequate angular resolution). If the relative
efficiency is of order unity, the star formation is proportional to the
mass of gas, if some kind of induced star formation is present, the
relative efficiency should be considerably larger than unity.