Journal Article

The stellar populations of M33's outer regions – IV. Inflow history and chemical evolution

Michael K. Barker and A. Sarajedini

in Monthly Notices of the Royal Astronomical Society

Published on behalf of The Royal Astronomical Society

Volume 390, issue 2, pages 863-880
Published in print October 2008 | ISSN: 0035-8711
Published online October 2008 | e-ISSN: 1365-2966 | DOI:
The stellar populations of M33's outer regions – IV. Inflow history and chemical evolution

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We have modelled the observed colour–magnitude diagram (CMD) at one location in M33's outskirts under the framework of a simple chemical evolution scenario which adopts instantaneous and delayed recycling for the nucleosynthetic products of Type II and Ia supernovae. In this scenario, interstellar gas forms stars at a rate modulated by the Kennicutt–Schmidt relation and gas outflow occurs at a rate proportional to the star formation rate (SFR). With this approach, we put broad constraints on the role of gas flows during this region's evolution and compare its [α/Fe] versus [Fe/H] relation with that of other Local Group systems. We find that models with gas inflow are significantly better than the closed-box model at reproducing the observed distribution of stars in the CMD. The best models have a majority of gas inflow taking place in the last 7 Gyr, and relatively little in the last 3 Gyr. These models predict most stars in this region to have [α/Fe] ratios lower than the bulk of the Milky Way's halo. The predictions for the present-day SFR, gas mass and oxygen abundance compare favourably to independent empirical estimates. Our results paint a picture in which M33's outer disc formed from the protracted inflow of gas over several Gyr with at least half of the total inflow occurring since z∼ 1.

Keywords: galaxies: abundances; galaxies: evolution; galaxies: individual: Messier Number: M33; Local Group; galaxies: spiral; galaxies: stellar content

Journal Article.  14365 words.  Illustrated.

Subjects: Astronomy and Astrophysics

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