How Young are Early-type Cluster Galaxies? Quantifying the Young Stellar Component in a Rich Cluster at z=0.41
Abstract
We present a new method of quantifying the mass fraction of young stars in galaxies by analyzing near-ultraviolet (NUV)-optical colors. We focus our attention on early-type cluster galaxies, whose star formation history is at present undetermined. Rest-frame NUV (F300W) and optical (F702W) images of cluster Abell 851 (z=0.41) using Hubble Space Telescope/WFPC2 allow us to determine an NUV-optical color-magnitude relation, whose slope is incompatible with a monolithic scenario for star formation at high redshift. A degeneracy between a young stellar component and its fractional mass contribution to the galaxy is found, and a photometric analysis comparing the data with the predictions for a simple two-stage star formation history is presented. The analysis shows that some of the early-type galaxies may have fractions higher than 10% of the total mass content in stars formed at z~0.5. An increased scatter is found in the color-magnitude relation at the faint end, resulting in a significant fraction of faint blue early-type systems. This would imply that less massive galaxies undergo more recent episodes of star formation, and this can be explained in terms of a positive correlation between star formation efficiency and luminosity. Work based on observations made with the NASA/ESA Hubble Space Telescope, obtained from the data archive at the Space Telescope Science Institute. STScI is operated by the Association of Universities for Research in Astronomy, Inc. under NASA contract NAS5-26555.
- Publication:
-
The Astrophysical Journal
- Pub Date:
- October 2000
- DOI:
- 10.1086/312898
- arXiv:
- arXiv:astro-ph/0008493
- Bibcode:
- 2000ApJ...541L..37F
- Keywords:
-
- Galaxies: Clusters: Individual: Name: Abell 851;
- Galaxies: Clusters: Individual: Alphanumeric: Cl 0939+4713;
- Galaxies: Elliptical and Lenticular;
- cD;
- Galaxies: Evolution;
- Galaxies: Formation;
- Astrophysics
- E-Print:
- Accepted for publication in ApJ Letters. Uses emulateapj.sty. 5 pages with 3 embedded EPS figures