|
Документ взят из кэша поисковой машины. Адрес
оригинального документа
: http://www.mrao.cam.ac.uk/~bn204/galevol/clemensetal08.html
Дата изменения: Mon Apr 4 13:47:52 2016 Дата индексирования: Sun Apr 10 07:11:25 2016 Кодировка: ISO8859-5 Поисковые слова: п п п п п п п п п п п п п п п п п п п п п п п п п п п п п п п п п п п п п п |
We define a volume limited sample of over 14,000 early-type galaxies (ETGs) selected from data release six of the Sloan Digital Sky Survey. The density of environment of each galaxy is robustly measured. By comparing narrow band spectral line indices with recent models of simple stellar populations (SSPs) we investigate trends in the star formation history as a function of galaxy mass (velocity dispersion), density of environment and galactic radius. We find that age, metallicity and a-enhancement all increase with galaxy mass and that field ETGs are younger than their cluster counterparts by about 2 Gyr. We find negative radial metallicity gradients for all masses and environments, and positive radial age gradients for ETGs with velocity dispersion over 180 kmsУ?1. Our results are qualitatively consistent with a relatively simple picture for ETG evolution in which the low-mass halos accreted by a proto-ETG contained not only gas but also a stellar population. This fossil population is preferentially found at large radii in massive ETGs because the stellar accretions were dissipationless.We estimate that the typical, massive ETG should have been assembled at z less than 3.5.
The catalogues are available in a plain ASCII format (compressed with bzip2), with one row for each galaxy in the catalogue. Please reference the catalogues by citing the paper above.
The galaxies in the catalogues below may be cross-correlated with other SDSS data products through the use of the (mjd, plateid, fiberid) tuples.
| Column Name | Units | Description |
|---|---|---|
| Pmjd | Days | MJD of the SDSS observation of the galaxy |
| Pplate | none | SDSS plate number of the observation of the galaxy |
| Pfid | none | SDSS fibre ID of the observation of the galaxy |
| Pz_helio | none | Redshift of the galaxy (heliocentric reference frame) |
| PC_r | none | Concentration index calculated in the r-band |
| Phalfl | arcsec | The Petrosian half-light radius measured in r-band |
| PDDist | MPc | Luminosity distance to the galaxy |
| PDensCr | Density measure | |
| Pvel_dis | km/s | The galaxy velocity dispersion as measured by the SDSS spectroscopic pipeline |