The Origin of Star Formation in Early-type Galaxies Inferred from Spatially Resolved Spectroscopy

TL;DR

This study uses spatially resolved spectroscopy to explore the origins and properties of star formation in early-type galaxies, revealing external gas accretion as a key factor.

Contribution

It provides new insights into the star formation history and physical properties of early-type galaxies with current star formation, highlighting external gas accretion as a primary cause.

Findings

Star-forming early-type galaxies have two star formation episodes.

Their properties resemble late-type galaxies but with more concentrated and kinematically misaligned gas.

External processes like mergers or gas accretion likely trigger star formation.

Abstract

We investigate the origin of star formation activity in early-type galaxies with current star formation using spatially resolved spectroscopic data from the Mapping Nearby Galaxies at APO (MaNGA) in the Sloan Digital Sky Survey (SDSS). We first identify star-forming early-type galaxies from the SDSS sample, which are morphologically early-type but show current star formation activity in their optical spectra. We then construct comparison samples with different combinations of star formation activity and morphology, which include star-forming late-type galaxies, quiescent early-type galaxies and quiescent late-type galaxies. Our analysis of the optical spectra reveals that the star-forming early-type galaxies have two distinctive episodes of star formation, which is similar to late-type galaxies but different from quiescent early-type galaxies with a single star formation episode. Star-forming early-type galaxies have properties in common with star-forming late-type galaxies, which include stellar population, gas and dust content, mass and environment. However, the physical properties of star-forming early-type galaxies derived from spatially resolved spectroscopy differ from those of star-forming late-type galaxies in the sense that the gas in star-forming early-type galaxies is more concentrated than their stars, and is often kinematically misaligned with stars. The age gradient of star-forming early-type galaxies also differs from those of star-forming late-type galaxies. Our findings suggest that the current star formation in star-forming early-type galaxies has an external origin including galaxy mergers or accretion gas from the cosmic web.