2006/10/25 by Raúl Jiménez, Raul Jimenez, Mariangela Bernardi +5 · 4 citations
Physics and Astronomy · #Astronomy #Astronomy and Astrophysical Research #Astrophysics #Galaxies: Formation, Evolution, Phenomena #Galaxy #Metallicity #Physics #Redshift #Sky #Star formation #Stellar mass #Stellar population #Stellar, planetary, and galactic studies #Velocity dispersion #astro-ph
paper · pdf · doi:10.1086/521323
Submitted to ApJ
arxiv created 2006/10/25 · openalex publication_date 2007/11/10 · arxiv updated 2009/12/01 · openalex created_date 2025/10/10 · openalex updated_date 2026/08/05
We use the spectra of ~22,000 early-type galaxies, selected from the Sloan Digital Sky Survey, to infer the ages, metallicities, and star formation histories of these galaxies. We find clear evidence of "downsizing," i.e., that galaxies with larger velocity dispersion have older stellar populations. In particular, we find that most early-type galaxies with velocity dispersion exceeding 200 km s -1 formed more than 90% of their current stellar mass at redshift z > 2.5. Therefore, star formation was suppressed around this redshift. We also show that chemical enrichment was rapid, lasting 1-2 Gyr, and find evidence that [Fe/H] is subsolar. We study the robustness of these results by comparing three different approaches: (1) using Lick absorption line indices, (2) fitting a single-burst stellar population model to the whole spectrum (lines and continuum), and (3) reconstructing the star formation and metallicity histories in multiple age bins, providing a method to measure mass-weighted ages and metallicities. We find good agreement between the luminosity-weighted ages and metallicities computed with these three methods.