Differential stellar population models: how to reliably measure [Fe/H] and [alpha/Fe] in galaxies

TL;DR

This paper introduces differential stellar population models that improve the measurement of [Fe/H] and [alpha/Fe] in galaxies by providing more accurate spectral fitting, validated on globular clusters and early-type galaxies.

Contribution

The paper presents a novel differential modeling approach calibrated at solar abundances, enhancing the accuracy of abundance ratio determinations in stellar populations.

Findings

Accurate fits to globular cluster spectra with inferred abundances matching other methods.

Better spectral fits for massive ellipticals using alpha-enhanced models.

Demonstrated potential for high-precision abundance measurements in galaxies.

Abstract

We present differential stellar population models, which allow improved determinations of the ages, iron and alpha-element abundances of old stellar populations from spectral fitting. These new models are calibrated at solar abundances using the predictions from classical, semi-empirical stellar population models. We then use the predictive power of fully synthetic models to compute predictions for different [Fe/H] and [alpha/Fe]. We show that these new differential models provide remarkably accurate fits to the integrated optical spectra of the bulge globular clusters NGC6528 and NGC6553, and that the inferred [Fe/H] and [alpha/Fe] agree with values derived elsewhere from stellar photometry and spectroscopy. The analysis of a small sample of SDSS early-type galaxies further confirms that our alpha-enhanced models provide a better fit to the spectra of massive ellipticals than the solar-scaled ones. Our approach opens new opportunities for precision measurements of abundance ratios in galaxies.