The age of blue LSB galaxies

TL;DR

This study uses hydrodynamic and population synthesis models to identify observational signatures that can constrain the age of blue low surface brightness galaxies, suggesting they are at least 1.5-6 billion years old.

Contribution

It introduces a combined modeling approach to estimate the ages of blue LSB galaxies using chemical and photometric indicators, providing minimum age constraints.

Findings

Blue LSB galaxies likely have a minimum age of 1.5-3 Gyr based on colors and oxygen abundance.

Equivalent widths of H-alpha suggest a larger minimum age of 5-6 Gyr.

No evidence indicates blue LSB galaxies are younger than 13 Gyr.

Abstract

(Abridged). Low metallicities, large gas-to-star mass ratios, and blue colors of most low surface brightness (LSB) galaxies imply that these systems may be younger than their high surface brightness counterparts. We seek to find observational signatures that can help to constrain the age of blue LSB galaxies. We use numerical hydrodynamic modelling to study the long-term (~13 Gyr) dynamical and chemical evolution of blue LSB galaxies adopting a sporadic scenario for star formation. Our models utilize various rates of star formation and different shapes of the initial mass function (IMF). We complement hydrodynamic modelling with population synthesis modelling to produce the integrated B-V colors and Halpha equivalent widths (EW(Ha)). We find that the mean oxygen abundances, B-V colors, EW(Ha), and the radial fluctuations in the oxygen abundance, when considered altogether, can be used to constrain the age of blue LSB galaxies if some independent knowledge of the IMF is available. Our modelling strongly suggests the existence of a minimum age for blue LSB galaxies. Model B-V colors and mean oxygen abundances set a tentative minimum age at 1.5-3.0 Gyr, whereas model EW(Ha) suggest a larger value of order 5-6 Gyr. The latter value may decrease somewhat, if blue LSB galaxies host IMFs with a truncated upper mass limit. We found no firm evidence that the age of blue LSB galaxies is significantly smaller than 13 Gyr.