Star formation in outer rings of S0 galaxies. II. NGC 4513 -- a multi-spin ringed S0 galaxy

TL;DR

This study investigates the star formation in the outer ring of the S0 galaxy NGC 4513, revealing external gas accretion and long-term star formation processes that differ from typical spiral galaxy behavior.

Contribution

It provides detailed spectroscopic analysis of NGC 4513's ring, demonstrating external gas origin and long-term star formation history in a seemingly 'red and dead' galaxy.

Findings

Gas in the ring is ionized by young stars.

Gas metallicity is slightly subsolar, matching the main disk.

The stellar mass in the ring exceeds current star formation estimates.

Abstract

Though S0 galaxies are usually thought to be `red and dead', they demonstrate often star formation organized in ring structures. We try to clarify the nature of this phenomenon and its difference from star formation in spiral galaxies. The moderate-luminosity nearby S0 galaxy, NGC 4513, is studied here. By applying long-slit spectroscopy along the major axis of NGC 4513, we have measured gas and star kinematics, Lick indices for the main body of the galaxy, and strong emission-line flux ratios in the ring. After inspecting the gas excitation in the ring using the line ratios diagnostic diagrams and have assured that it is ionized by young stars, we have determined the gas oxygen abundance by using popular strong-line calibration methods. We have estimated star formation rate (SFR) in the outer ring by using the archival Galaxy Evolution Explorer (GALEX) ultraviolet images of the galaxy. The ionized gas counterrotates the stars over the whole extension of NGC 4513 so being accreted from outside. The gas metallicity in the ring is slightly subsolar, [O/H]=-0.2 dex, matching the metallicity of the stellar component of the main galactic disc. However the stellar component of the ring is much more massive than can be explained by the current star formation level in the ring. We conclude that probably the ring of NGC 4513 is a result of tidal disruption of a massive gas-rich satellite, or it may be a consequence of a long star-formation event provoked by a gas accretion from a cosmological filament having started some 3 Gyr ago.