The impact of starbursts on element abundance ratios
Abstract
We investigate the impact of bursts in star formation on the predictions of one-zone chemical evolution models, adopting oxygen (O), iron (Fe), and strontium (Sr), as representative α, iron-peak, and s-process elements, respectively. To this end, we develop and make use of the Versatile Integrator for Chemical Evolution (VICE), a PYTHON package designed to handle flexible user-specified evolutionary parameters. Starbursts driven by a temporary boost of gas accretion rate create loops in [O/Fe]-[Fe/H] evolutionary tracks and a peak in the stellar [O/Fe] distribution at intermediate values. Bursts driven by a temporary boost of star formation efficiency have similar effects, and they also produce a population of α-deficient stars during the depressed star formation phase following the burst. This α-deficient population is more prominent if the outflow rate is tied to a time-averaged star formation rate (SFR) instead of the instantaneous SFR. Theoretical models of Sr production predict a strong metallicity dependence of supernova and asymptotic giant branch star yields, though comparison to data suggests an additional, nearly metallicity-independent source. Evolution of [Sr/Fe] and [Sr/O] during a starburst is complex because of this metallicity dependence and the multiple time-scales at play. Moderate amplitude (10-20 per cent) sinusoidal oscillations in SFR produce loops in [O/Fe]-[Fe/H] tracks and multiple peaks in [O/Fe] distributions, a potential source of intrinsic scatter in observed sequences. We investigate the impact of a factor ~2 enhancement of Galactic star formation ~2 Gyr ago, as suggested by some recent observations. VICE is publicly available at <http://pypi.org/project/vice/>.
- Publication:
-
Monthly Notices of the Royal Astronomical Society
- Pub Date:
- October 2020
- DOI:
- 10.1093/mnras/staa2431
- arXiv:
- arXiv:1911.02598
- Bibcode:
- 2020MNRAS.498.1364J
- Keywords:
-
- methods: numerical;
- galaxies: abundances;
- galaxies: evolution;
- galaxies: star formation;
- galaxies: stellar content;
- Astrophysics - Astrophysics of Galaxies
- E-Print:
- 17 pages