Bibcode
Tenorio-Tagle, G.; Palouš, J.; Silich, S.; Medina-Tanco, G. A.; Muñoz-Tuñón, C.
Bibliographical reference
Astronomy and Astrophysics, v.411, p.397-404 (2003)
Advertised on:
12
2003
Journal
Citations
18
Refereed citations
13
Description
Here we model a star forming factory in which the continuous creation of
stars results in a highly concentrated, massive (globular cluster-like)
stellar system. We show that under very general conditions a large-scale
gravitational instability in the ISM, which triggers the collapse of a
massive cloud, leads with the aid of a spontaneous first generation of
massive stars, to a standing, small-radius, cold and dense shell.
Eventually, as more of the collapsing matter is processed and
incorporated, the shell becomes gravitationally unstable and begins to
fragment, allowing the formation of new stars, while keeping its
location. This is due to a detailed balance established between the ram
pressure from the collapsing cloud which, together with the
gravitational force exerted on the shell by the forming cluster, acts
against the mechanical energy deposited by the collection of new stars.
We present a full analysis of feedback and show how the standing shell
copes with the increasing mechanical energy generated by an increasing
star-formation rate. The latter also leads to a rapidly growing number
of ionizing photons, and we show that these manage to ionize only the
inner skin of the standing star-forming shell. We analyze the mass
spectrum of fragments that result from the continuous fragmentation of
the standing shell and show that its shape is well approximated at the
high mass end by a power law with slope -2.25, very close to the value
that fits the universal IMF. Furthermore, it presents a maximum near to
one solar mass and a rapid change towards a much flatter slope for
smaller fragments. The self-contamination resultant from the continuous
generation of stars is shown to lead to a large metal spread in massive
( ~ 106 M_sun) clusters, while clusters with a mass similar
to 105 M_sun or smaller, simply reflect the initial
metalicity of the collapsing cloud. This is in good agreement with the
data available for globular clusters in the Galaxy. Other observables
such as the expected IR luminosity and the H_alpha equivalent width
caused by the forming clusters are also calculated.