The link between the star formation history and [α/Fe ]
Abstract
The abundance ratios between key elements such as iron and α-process elements carry a wealth of information on the star formation history (SFH) of galaxies. So far, simple chemical evolution models have linked [α/Fe ] with the SFH time-scale, correlating large abundance ratios with short-lived SFH. The incorporation of full spectral fitting to the analysis of stellar populations allows for a more quantitative constraint between [α/Fe ] and the SFH. In this letter, we provide, for the first time, an empirical correlation between [α/Fe ] (measured from spectral indices) and the SFH (determined via a non-parametric spectral-fitting method). We offer an empirical version of the iconic outline of Thomas et al., relating star formation time-scale with galaxy mass, although our results suggest, in contrast, a significant population of old (≳10 Gyr) stars even for the lowest mass ellipticals (M/dyn ∼ 3 × 1010 M⊙). In addition, the abundance ratio is found to be strongly correlated with the time to build up the stellar component, showing that the highest [α/Fe ] (≳+0.2) are attained by galaxies with the shortest half-mass formation time (≲2 Gyr), or equivalently, with the smallest (≲40 per cent) fraction of populations younger than 10 Gyr. These observational results support the standard hypothesis that star formation incorporates the Fe-enriched interstellar medium into stars, lowering the high abundance ratio of the old populations.
- Publication:
-
Monthly Notices of the Royal Astronomical Society
- Pub Date:
- November 2011
- DOI:
- 10.1111/j.1745-3933.2011.01146.x
- arXiv:
- arXiv:1109.0005
- Bibcode:
- 2011MNRAS.418L..74D
- Keywords:
-
- galaxies: elliptical and lenticular;
- cD;
- galaxies: evolution;
- galaxies: formation;
- galaxies: stellar content;
- galaxies: structure;
- Astrophysics - Cosmology and Nongalactic Astrophysics
- E-Print:
- 5 pages, 2 figures. Accepted for publication in MNRAS Letters