# Star-forming rings in lenticular galaxies: origin of the gas

## TL;DR

This study investigates the origins and properties of star-forming rings in lenticular galaxies using SALT spectroscopy, revealing recent gas accretion, ongoing star formation, and variations in star formation activity across different galaxies.

## Contribution

It provides new insights into the gas accretion and star formation processes in UV-bright rings of S0 galaxies through detailed spectroscopic analysis.

## Key findings

- Most rings show active star formation with 0.1-0.2 solar masses per year.
- Chemical analysis indicates recent gas accretion with near-solar metallicity.
- Star formation rates decline rapidly, with some rings having ceased star formation.

## Abstract

Rings in S0s are enigmatic features which can however betray the evolutionary paths of particular galaxies. We have undertaken long-slit spectroscopy of five lenticular galaxies with UV-bright outer rings. The observations have been made with the Southern African Large Telescope (SALT) to reveal the kinematics, chemistry, and the ages of the stellar populations and the gas characteristics in the rings and surrounding disks. Four of the five rings are also bright in the H-alpha emission line, and the spectra of the gaseous rings extracted around the maxima of the H-alpha equivalent width reveal excitation by young stars betraying current star formation in the rings. The integrated level of this star formation is 0.1-0.2 solar mass per year, with the outstanding value of 1 solar mass per year in NGC 7808. The difference of chemical composition between the ionized gas of the rings which demonstrate nearly solar metallicity and the underlying stellar disks which are metal-poor implies recent accretion of the gas and star formation ignition; the star formation history estimated by using different star formation indicators implies that the star formation rate decreases with e-folding time of less than 1 Gyr. In NGC 809 where the UV-ring is well visible but the H-alpha emission line excited by massive stars is absent, the star formation has already ceased.