The Sloan Digital Sky Survey(SDSS) is a redshift factory producing more than 5000 spectra a night when conditions allow. In order not to fall behind the data acquisition, highly automated and accurate spectral reduction pipelines are needed to process the data. Also the varied nature of SDSS target selection: the main galaxy sample, the large red galaxy sample, the QSO sample, stellar targets, and serendipitous objects; requires the pipeline to be adept at handling the full range of astronomical spectra, from a redshift of 0 out to a redshift of 6. The SDSS spectra are of exceptionally high quality, allowing the pipeline not only to determine redshifts and broadly classify the spectra, but also measure line parameters, calculate spectral indices, velocity dispersions etc. The purpose of this summary is to give an overview of the workings of the pipeline and its outputs, and give some guidance in using those outputs.
A sample of nearly 9000 early-type galaxies, observed in the g*,r*,i*, and z* bands, was selected from the Sloan Digital Sky Survey using morphological and spectral criteria. The sample spans the redshift range 0 < z < 0.3, and was used to study how early-type galaxy observables, including luminosity, effective radius, surface brightness, color, velocity dispersion, and chemical abundances are correlated with one another, how they evolve, and whether they depend on environment.
Relative to the population at z~0.1, the median redshift of the sample, galaxies at lower and higher redshifts have evolved little. The luminosities and colors, the Fundamental Plane, and absorption- line strengths (obtained from co-added spectra of similar objects) suggest that the population is evolving passively, having formed the bulk of its stars about 9 Gyrs ago. While the Fundamental Plane suggests that galaxies in dense regions are slightly different from galaxies in less dense regions, the chemical abundances and color-velocity dispersion relations show no statistically significant environmental dependence.
That we are able to measure velocity dispersions at all is a tribute to the quality of the SDSS spectrographs: they exceed the goals for which they were designed.
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