EDP Sciences
Free access
Volume 435, Number 2, May IV 2005
Page(s) 551 - 561
Section Galactic structure, stellar clusters and populations
DOI http://dx.doi.org/10.1051/0004-6361:20042308

A&A 435, 551-561 (2005)
DOI: 10.1051/0004-6361:20042308

Stochastic processes, galactic star formation, and chemical evolution

Effects of accretion, stripping, and collisions in multiphase multi-zone models
G. Valle1, S. N. Shore1, 2 and D. Galli3

1  Dipartimento di Fisica "Enrico Fermi", Università di Pisa, largo Pontecorvo 3, Pisa 56127, Italy
    e-mail: valle@df.unipi.it
2  INFN/Pisa, largo Pontecorvo 3, Pisa 56127, Italy
3  INAF - Osservatorio Astrofisico di Arcetri, largo Enrico Fermi 5, Firenze 50125, Italy

(Received 3 November 2004 / Accepted 3 February 2005 )

This paper reports simulations allowing for stochastic accretion and mass loss within closed and open systems modeled using a previously developed multi-population, multi-zone (halo, thick disk, thin disk) treatment. The star formation rate is computed as a function of time directly from the model equations and all chemical evolution is followed without instantaneous recycling. Several types of simulations are presented here: (1) a closed system with bursty mass loss from the halo to the thick disk, and from the thick to the thin disk, in separate events to the thin disk; (2) open systems with random environmental (extragalactic) accretion, e.g. by infall of high velocity clouds directly to the thin disk; (3) schematic open system single and multiple collision events and intracluster stripping. For the open models, the mass of the Galaxy has been explicitly tracked with time. We present the evolution of the star formation rate, metallicity histories, and concentrate on the light elements. We find a wide range of possible outcomes, including an explanation for variations in the Galactic D/H ratio, and highlight the problems for uniquely reconstructing star forming histories from contemporary abundance measurements.

Key words: galaxies: evolution -- galaxies: abundances -- galaxies: interactions

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