The detailed abundance patterns of the stars within galaxies provide a unique window into the history of star formation ( SF ) at early times .
Two widely used ‘ chronometers ’ include the \alpha and iron-peak elements , which are created on short and long timescales , respectively .
These two clocks have been widely used to estimate SF timescales from moderate-resolution spectra of early-type galaxies .
Elements formed via s -process neutron captures ( e.g. , Sr and Ba ) comprise a third type of chronometer , as the site of the main s -process is believed to be intermediate and low-mass asymptotic giant branch stars .
The [ \alpha /Ba ] ratio in particular should provide a powerful new constraint on the SF histories of galaxies , in part because it is insensitive to the uncertain distribution of Type Ia SNe detonation times and the overall Ia rate .
Here we present new measurements of the abundance of Sr and Ba in nearby early-type galaxies by applying stellar population synthesis tools to high S/N optical spectra .
We find a strong anti-correlation between [ Mg/Fe ] and [ Ba/Fe ] , and a strong positive correlation between [ Mg/Ba ] and galaxy velocity dispersion .
These trends are consistent with the idea that more massive galaxies formed their stars on shorter timescales compared to less massive galaxies , and rule out several other proposed explanations for the observed super-solar [ Mg/Fe ] values in massive galaxies .
In contrast , [ Sr/Fe ] \sim 0 , with no strong variation across the sample .
It is difficult to interpret the Sr trends without detailed chemical evolution models owing to the multiplicity of proposed nucleosynthetic sites for Sr .