Integrated Stellar Populations: Confronting Photometry with Spectroscopy

TL;DR

This study assesses how spectroscopic and photometric data can be combined to accurately determine star formation histories in spiral galaxy bulges, emphasizing the importance of detailed stellar population models including the TP-AGB phase.

Contribution

It demonstrates that incorporating a complete TP-AGB phase in stellar population models improves the match between observed and predicted galaxy colors, refining SFH and stellar population analyses.

Findings

Spectroscopy reveals recent star formation significantly affects V-band flux.

Including full TP-AGB treatment in models aligns predicted and observed optical-NIR colors.

Models without complete TP-AGB phases underestimate NIR flux and produce bluer colors.

Abstract

We investigate the ability of spectroscopic techniques to yield realistic star formation histories (SFHs) for the bulges of spiral galaxies based on a comparison with their observed broadband colors. Full spectrum fitting to optical spectra indicates that recent (within ~1 Gyr) star formation activity can contribute significantly to the V-band flux, whilst accounting for only a minor fraction of the stellar mass budget which is made up primarily of old stars. Furthermore, recent implementations of stellar population (SP) models reveal that the inclusion of a more complete treatment of the thermally pulsating asymptotic giant branch (TP-AGB) phase to SP models greatly increases the NIR flux for SPs of ages 0.2-2 Gyr. Comparing the optical--NIR colors predicted from population synthesis fitting, using models which do not include all stages of the TP-AGB phase, to the observed colors reveals that observed optical--NIR colors are too red compared to the model predictions. However, when a 1 Gyr SP from models including a full treatment the TP-AGB phase is used, the observed and predicted colors are in good agreement. This has strong implications for the interpretation of stellar populations, dust content, and SFHs derived from colors alone.