Composite Stellar Populations and Element by Element Abundances in the Milky Way Bulge and Elliptical Galaxies

TL;DR

This study models the integrated-light properties of the Milky Way bulge with realistic abundance distributions and compares them to elliptical galaxies, revealing similarities and key differences in element trends and spectral features.

Contribution

It introduces realistic abundance distribution functions in modeling stellar populations and compares their spectral signatures to those of elliptical galaxies, highlighting new insights into chemical abundance patterns.

Findings

MW bulge models better match elliptical galaxies than local stars.

Fe, Ti, Mg trends are similar in bulge and ellipticals, but C, Na, Ca differ.

Systematic effects in abundance and age recovery are minor, with promising methods for measuring ADF width.

Abstract

This paper explores the integrated-light characteristics of the Milky Way (MW) bulge and to what extent they match those of elliptical galaxies in the local universe. We model composite stellar populations with realistic abundance distribution functions (ADFs), tracking the trends of individual elements as a function of overall heavy element abundance as actually observed in MW bulge stars. The resultant predictions for absorption feature strengths from the MW bulge mimic elliptical galaxies better than solar neighborhood stars do, but the MW bulge does not match elliptical galaxies, either. Comparing bulge versus elliptical galaxies, Fe, Ti, and Mg trend about the same for both but C, Na, and Ca seem irreconcilably different. Exploring the behavior of abundance compositeness leads to the concepts of "red lean" where a narrower ADF appears more metal rich than a wide one, and "red spread" where the spectral difference between wide and narrow ADFs increases as the ADF peak is moved to more metal-rich values. Tests on the systematics of recovering abundance, abundance pattern, and age from composite stellar populations using single stellar population models were performed. The chemical abundance pattern was recovered adequately, though a few minor systematic effects were uncovered. The prospects of measuring the width of the ADF of an old stellar population were investigated and seem bright using UV to IR photometry.