AAS Meeting #194 - Chicago, Illinois, May/June 1999
Session 35. Star, Cluster, Galaxy Formation and Evolution
Oral, Monday, May 31, 1999, 2:00-3:30pm, Marquette

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[35.03] Formation of Globular Clusters via Shocks in Starburst Galaxies and Protogalaxies

L. Ozernoy (GMU \& GSFC/NASA)

I analyze the formation of so called `super star clusters' (SSCs) from shock-compressed giant molecular clouds (GMCs). Depending on the environment, parameters of the forming SSCs can vary. Three different environments are analyzed: (I)~the central part of an isolated galaxy; (II)~colliding galaxies; and (III)~protogalactic clouds. Dependence of cluster parameters upon various gas cloud characteristics (velocity, density, temperature, and chemical abundance) is discussed.

Case I is exemplified by a collisionally-induced star formation in the central part of the Milky Way Galaxy1, which is characterized by relatively low velocities of colliding GMCs.

Case II concerns starburst galaxies and is modelled by head-on collisions of galaxies (oblique collision case is examined as well). The cloud-cloud collisions trigger, during the time when the central parts of galaxies cross each other, gravitational instability in the bulk of the GMCs. The proposed model explains the basic observational features of SSCs: (i) appearance in irregular and spiral galaxies of all types; (ii) a weak dependence of the formation process on metallicity of gas; (iii) a more or less simultaneous formation of ~05-106 stars in each GMC before the gas as a building material is blown out. The unambiguous signature of this model is that the ages of globular clusters in a given galaxy would reveal a distribution in the form of discrete peaks (each related to the corresponding collision of the parent galaxy) rather than be distributed continuously.

Case III deals with globular cluster formation prior to, or in parallel with, galaxy formation via collisions of protogalactic clouds2.

\renewcommand \baselinestretch{0.2} { (Eds. S.S. Holt & L.G. Mundy). AIP Conf. Proc. 393, 323\\ 2Ozernoy, L.M., 1989, ``Primeval and `Rejuvenated' Galaxies", in Ann. New York\\ {\hbox{~~~} Acad. Sci.} 571, 219}

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