Stellar Populations and the Star Formation Histories of LSB Galaxies: III. Stellar Population Models

TL;DR

This paper develops stellar population models to understand the star formation history of gas-rich, low surface brightness galaxies, finding they are best explained by constant star formation with recent weak bursts.

Contribution

It introduces detailed population models incorporating multi-metallicity and evolved stellar components to match observations of LSB galaxies.

Findings

LSB galaxies are consistent with constant star formation histories.

Color variations are explained by recent weak star formation bursts.

Early-type spirals are better fit by declining star formation models.

Abstract

A series of population models are designed to explore the star formation history of gas-rich, low surface brightness (LSB) galaxies. LSB galaxies are unique in having properties of very blue colors, low H$\alpha$ emission and high gas fractions that indicated a history of constant star formation (versus the declining star formation models used for most spirals and irregulars). The model simulations use an evolving multi-metallicity composite population that follows a chemical enrichment scheme based on Milky Way observations. Color and time sensitive stellar evolution components (i.e., BHB, TP-AGB and blue straggler stars) are included, and model colors are extended into the Spitzer wavelength regions for comparison to new observations. In general, LSB galaxies are well matched to the constant star formation scenario with the variation in color explained by a fourfold increase/decrease in star formation over the last 0.5 Gyrs (i.e., weak bursts). Early-type spirals, from the S$^4$G sample, are better fit by a declining star formation model where star formation has decreased by 40% in the last 12 Gyrs.