Volume 520, September-October 2010
|Number of page(s)||11|
|Section||Galactic structure, stellar clusters, and populations|
|Published online||27 September 2010|
Chemical evolution models for spiral disks: the Milky Way, M 31, and M 33
Dipartimento di Fisica, Sezione di Astronomia, Università di Trieste, via GB Tiepolo 11, 34131 Trieste, Italy e-mail: firstname.lastname@example.org
2 Instituto de Astronomia, Geofísica e Ciências Atmosféricas (IAG), Universidade de São Paulo, Rua do Matão, 1226 Cidade Universitária, São Paulo - SP 05508-900, Brazil
3 INAF Osservatorio Astronomico di Trieste, via GB Tiepolo 11, 34131 Trieste, Italy
Accepted: 22 April 2010
Context. The distribution of chemical abundances and their variation with time are important tools for understanding the chemical evolution of galaxies. In particular, the study of chemical evolution models can improve our understanding of the basic assumptions made when modelling our Galaxy and other spirals.
Aims. We test a standard chemical evolution model for spiral disks in the Local Universe and study the influence of a threshold gas density and different efficiencies in the star formation rate (SFR) law on radial gradients of abundance, gas, and SFR. The model is then applied to specific galaxies.
Methods. We adopt a one-infall chemical evolution model where the Galactic disk forms inside-out by means of infall of gas, and we test different thresholds and efficiencies in the SFR. The model is scaled to the disk properties of three Local Group galaxies (the Milky Way, M 31 and M 33) by varying its dependence on the star formation efficiency and the timescale for the infall of gas onto the disk.
Results. Using this simple model, we are able to reproduce most of the observed constraints available in the literature for the studied galaxies. The radial oxygen abundance gradients and their time evolution are studied in detail. The present day abundance gradients are more sensitive to the threshold than to other parameters, while their temporal evolutions are more dependent on the chosen SFR efficiency. A variable efficiency along the galaxy radius can reproduce the present day gas distribution in the disk of spirals with prominent arms. The steepness in the distribution of stellar surface density differs from massive to lower mass disks, owing to the different star formation histories.
Conclusions. The most massive disks seem to have evolved faster (i.e., with more efficient star formation) than the less massive ones, thus suggesting a downsizing in star formation for spirals. The threshold and the efficiency of star formation play a very important role in the chemical evolution of spiral disks. For instance, an efficiency varying with radius can be used to regulate the star formation. The oxygen abundance gradient can steepen or flatten in time depending on the choice of this parameter.
Key words: galaxies: abundances / galaxies: evolution / galaxies: spiral
© ESO, 2010
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