Yet another theory for the origin of halo globular clusters and spheroid stars

Abstract

view Abstract Citations (30) References (50) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Yet Another Theory for the Origin of Halo Globular Clusters and Spheroid Stars Vietri, Mario ; Pesce, Enrico Abstract 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 collisional H_2_ cooling), denser than average condensations implode because of the pressure of the surrounding hot, tenuous medium. Small condensations (M < 5 X 10^4^ M_sun_) are then returned by the bounced shock to the hot phase, and large condensations (corresponding to GC masses M_*_ > 6 x 10^5^ M_sun_) 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 H_2_, 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 V_c_^1/2^) 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 protoclusters is naturally enforced by turbulent mixing in the cold phase, before fragmentation into stars. Mass ranges for halo GCs (assuming a reasonable star formation efficiency) and velocity dispersion for spheroid stars in agreement with observations are predicted. Publication: The Astrophysical Journal Pub Date: April 1995 DOI: 10.1086/175465 Bibcode: 1995ApJ...442..618V Keywords: 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; Astrophysics; GALAXIES: COOLING FLOWS; GALAXY: GLOBULAR CLUSTERS: GENERAL; STARS: FORMATION full text sources ADS | data products SIMBAD (7) NED (7)