On the Incorporation of Metallicity Data into Star Formation History Measurements from Resolved Stellar Populations

TL;DR

Integrating spectroscopic metallicities with resolved star color-magnitude diagrams enhances the accuracy of star formation and chemical enrichment histories, but systematic uncertainties in stellar models limit further improvements.

Contribution

This paper introduces two methods for combining metallicity data with CMD fitting, improving SFH measurement precision and addressing systematic errors.

Findings

Joint fitting increases SFH accuracy by ~10%.

Systematics can be mitigated to match CMD-only precision.

Stellar model improvements are needed for further gains.

Abstract

The combination of spectroscopic stellar metallicities and resolved star color-magnitude diagrams (CMDs) has the potential to constrain the entire star formation and chemical enrichment history (SFH) of a galaxy better than fitting CMDs alone (as is most common in SFH studies using resolved stellar populations). In this paper, two approaches for incorporating external metallicity information into color-magnitude diagram fitting techniques are presented. Overall, the joint fitting of metallicity and CMD information can increase the precision on measured age-metallicity relationships and star formation rates by ~10% over CMD fitting alone. However, systematics in stellar isochrones and mismatches between spectroscopic and photometric metallicity determinations can reduce the accuracy of the recovered SFHs. I present a simple mitigation of these systematics that can reduce the amplitude of these systematics to the level obtained from CMD fitting alone, while ensuring the age-metallicity relationship is consistent with spectroscopic metallicities. As is the case in CMD-fitting analysis, improved stellar models and calibrations between spectroscopic and photometric metallicities are currently the primary impediment to gains in SFH precision from jointly fitting stellar metallicities and CMDs.