Astronomy and Astrophysics – Astrophysics
Scientific paper
Apr 1995
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1995apj...442..618v&link_type=abstract
Astrophysical Journal (ISSN 0004-637X), vol. 442, no. 2, Part 1, p. 618-627
Astronomy and Astrophysics
Astrophysics
28
Astronomical Models, Cooling Flows (Astrophysics), Early Stars, Galactic Evolution, Galactic Halos, Globular Clusters, Star Formation, Implosions, Interstellar Gas, Mathematical Models, Shock Fronts, Stellar Mass Accretion
Scientific paper
We consider the evolution of the gaseous, primordial (Z=0) Galaxy, as cooling drives its gravitational collapse. We show that it is possible to form halo globular clusters (GCs) and early spheroid stars before gas acquires angular momentum and settles in a disk. Owing to their short cooling times (including collisonal H2 cooling), denser than average condensations implode because of the pressure of the surrounding hot, tenuous medium. Small condensations (M less than 5 x 104 solar mass) are then returned by the bounced shock to the hot phase, and large condensations (corresponding to GC masses M* greater than 6 x 105 solar mass) fragment into stars in the dense shell behind the implosion shock before implosion is complete, thus generating the spheroid. Intermediate clouds, cooling to 100 K because of collisional excitation of H2, are compressed and left in approximate pressure equilibrium with the hot-phase, then they fragment into stars and give rise to halo GCs. The upper limit to the GC mass, our major result, displays only a weak dependence proportional to (ve exp 0.5) on Galactic parameters, making it a universal upper limit. The dependence upon overall Galactic metallicity is weak, so that current formation of GCs is allowed. Chemical homogeneity within photoclusters is naturally enforced by turbulent mixing in the cold phase, before fragmentation into stars. Mass ranges for halo GCs (assuming a resonable star formation efficiency) and velocity dispersion for spheroid stars in agreement with observations are predicted.
Pesce Enrico
Vietri Mario
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