2003/12/19 by M. Fukugita, Masataka Fukugita, Osamu Nakamura +4 · 4 citations
Physics and Astronomy · #Astronomy and Astrophysical Research #Galaxies: Formation, Evolution, Phenomena #Stellar, planetary, and galactic studies #astro-ph
paper · pdf · doi:10.1086/382151
published as Astrophys.J. 601 (2004) L127-L130 · Accepted for publication in Astrophys. J. Letters
arxiv created 2003/12/19 · openalex publication_date 2004/01/28 · arxiv updated 2009/12/01 · openalex created_date 2025/10/10 · openalex updated_date 2026/08/04
We report the discovery of actively star-forming elliptical galaxies in a morphologically classified sample of bright galaxies at a low redshift obtained from the Sloan Digital Sky Survey. The emission lines of these galaxies do not show the characteristics of active galactic nuclei, and thus their strong Hα emission is ascribed to star formation with a rate nearly as high as that seen in typical late spiral galaxies. This is taken as evidence against the traditional view that all elliptical galaxies formed early and now evolve only passively. The frequency of such star-forming elliptical galaxies is a few tenths of a percent in the sample but increases to 3% if we include active S0 galaxies. We can identify these galaxies as probable progenitors of so-called E+A galaxies that show the strong Balmer absorption feature of A stars superimposed on an old star population. The approximate match of the abundance of active elliptical plus S0 galaxies to that of E+A galaxies indicates that the duration of such late star formation episodes is of the order of ≳1 Gyr. If we interpret these galaxies as new additions to the early-type galaxy population, and if we assume a power law for their number evolution, the abundance of early-type galaxies at z = 1 is about 30% less than that at z = 0.