Recent Star-Forming Activity in Local Elliptical Galaxies

TL;DR

This study investigates recent star formation in local elliptical galaxies using SDSS data, revealing that a subset shows active star formation, younger stellar populations, and potential evolutionary links to E+A galaxies.

Contribution

It provides new insights into the star formation history and chemical evolution of elliptical galaxies, highlighting the presence of recent star-forming activity and its implications.

Findings

13 out of 487 ellipticals show recent star formation.

Star-forming ellipticals have younger ages and higher metallicity.

E+A galaxies may be transitional objects between star-forming and quiescent ellipticals.

Abstract

The formation and evolution of elliptical galaxies (EGs) is still an open question. In particular, recent observations suggest that elliptical galaxies are not only simple spheroidal systems of old stars. In this paper we analyze a sample of elliptical galaxies selected from the Sloan Digital Sky Survey in order to study the star-forming activity in local elliptical galaxies. Among these 487 ellipticals we find that 13 EGs show unambiguous evidence of recent star-formation activity betrayed by conspicuous nebular emission lines. Using the evolutionary stellar population synthesis models and Lick absorption line indices we derive stellar ages, metallicities, and $\alpha$-element abundances, and thus reconstruct the star formation and chemical evolution history of the star-forming elliptical galaxies (SFEGs) in our sample. We find that SFEGs have relative younger stellar population age, higher metallicity, and lower stellar mass, and that their star formation history can be well described by a recent minor and short starburst superimposed on old stellar component. We also detect 11 E+A galaxies whose stellar population properties are closer to those of quiescent (normal) ellipticals than to star-forming ones. However, from the analysis of their absorption line indices, we note that our E+A galaxies show a significant fraction of intermediate-age stellar populations, remarkably different from the quiescent galaxies. This might suggest an evolutionary link between E+As and star-forming ellipticals. Finally, we confirm the relations between age, metallicity, $\alpha$ element abundance, and stellar mass for local elliptical galaxies.