Stellar Population Trends in S0 Galaxies

TL;DR

This study analyzes stellar population age and metallicity gradients in 59 S0 galaxies using optical and near-infrared photometry, revealing common negative metallicity gradients and diverse age profiles that inform galaxy formation theories.

Contribution

It provides detailed radial stellar population profiles for a sizable S0 galaxy sample, extending previous work by combining optical and NIR data to analyze outer regions up to 5 effective radii.

Findings

Most galaxies show negative metallicity gradients.

A significant fraction have outer regions older than 10 Gyr.

Lower mass and less concentrated galaxies are younger and less metal-rich.

Abstract

We present stellar population age and metallicity trends for a sample of 59 S0 galaxies based on optical SDSS and NIR J & H photometry. When combined with optical g and r passband imaging data from the SDSS archive and stellar population models, we obtain radial age and metallicity trends out to at least 5 effective radii for most of the galaxies in our sample. The sample covers a range in stellar mass and light concentration. We find an average central light-weighted age of ~ 4 Gyr and central metallicity [Z/H] ~ 0.2 dex. Almost all galaxies show a negative metallicity gradient from the center out, with an average value of Delta[Z/H]/Delta(log(r/Re)) = -0.6. An age increase, decrease, and minimal change with radius is observed for 58%, 19%, and 23%, respectively, for a mean age gradient of Delta(age)/Delta(log(r/Re)) = 2.3 Gyr dex^{-1}. For 14 out of 59 galaxies, the light-weighted age of the outer region is greater than 10 Gyr. We find that galaxies with both lower mass and lower concentration have younger light-weighted ages and lower light-weighted metallicities. This mass-metallicity relation extends into the outer regions of our S0 galaxies. Our results are consistent with the formation of S0 galaxies through the transformation of spiral galaxy disks. Determining the structural component that makes up the outer region of galaxies with old outksirts is a necessary step to understand the formation history of S0 galaxies.