Person:

Eisenstein, Daniel

We combine Sloan Digital Sky Survey spectra of 22,000 luminous, red, bulge-dominated galaxies to get high signal-to-noise ratio average spectra in the rest-frame optical and ultraviolet (2600-7000 Å). The average spectra of these massive, quiescent galaxies are early type with weak emission lines and with absorption lines indicating an apparent excess of α-elements over solar abundance ratios. We make average spectra of subsamples selected by luminosity, environment, and redshift. The average spectra are remarkable in their similarity. What variations do exist in the average spectra as a function of luminosity and environment are found to form a nearly one-parameter family in spectrum space. We present a high signal-to-noise ratio spectrum of the variation. We measure the properties of the variation with a modified version of the Lick index system and compare to model spectra from stellar population syntheses. The variation may be a combination of age and chemical abundance differences, but the conservative conclusion is that the quality of the data considerably exceeds the current state of the models.

A sample of nearly 9000 early-type galaxies, in the redshift range 0.01 ≤ z ≤ 0.3, was selected from the Sloan Digital Sky Survey (SDSS) using morphological and spectral criteria. This paper describes how the sample was selected, presents examples of images and seeing-corrected fits to the observed surface brightness profiles, describes our method for estimating K-corrections, and shows that the SDSS spectra are of sufficiently high quality to measure velocity dispersions accurately. It also provides catalogs of the measured photometric and spectroscopic parameters. In related papers, these data are used to study how early-type galaxy observables, including luminosity, effective radius, surface brightness, color, and velocity dispersion, are correlated with one another.

A magnitude-limited sample of nearly 9000 early-type galaxies, in the redshift range 0.01 ≤ z ≤ 0.3, was selected from the Sloan Digital Sky Survey using morphological and spectral criteria. The sample was used to study how early-type galaxy observables, including luminosity L, effective radius Ro, surface brightness Io, color, and velocity dispersion σ, are correlated with one another. Measurement biases are understood with mock catalogs that reproduce all of the observed scaling relations and their dependences on fitting technique. At any given redshift, the intrinsic distribution of luminosities, sizes, and velocity dispersions in our sample are all approximately Gaussian. A maximum likelihood analysis shows that σ ∝ L0.25±0.012, Ro ∝ L0.63±0.025, and Ro ∝ I-0.75±0.02 in the r* band. In addition, the mass-to-light ratio within the effective radius scales as Mo/L ∝ L0.14±0.02 or Mo/L ∝ M, and galaxies with larger effective masses have smaller effective densities: Δo ∝ M. These relations are approximately the same in the g*, i*, and z* bands. Relative to the population at the median redshift in the sample, galaxies at lower and higher redshifts have evolved only little, with more evolution in the bluer bands. The luminosity function is consistent with weak passive luminosity evolution and a formation time of about 9 Gyr ago.

A magnitude-limited sample of nearly 9000 early-type galaxies in the redshift range 0.01 ≤ z ≤ 0.3 was selected from the Sloan Digital Sky Survey (SDSS) using morphological and spectral criteria. The fundamental plane relation in this sample is Ro ∝ σ1.49±0.05I in the r* band. It is approximately the same in the g*, i*, and z* bands. Relative to the population at the median redshift in the sample, galaxies at lower and higher redshifts have evolved only a little. If the fundamental plane is used to quantify this evolution, then the apparent magnitude limit can masquerade as evolution; once this selection effect has been accounted for, the evolution is consistent with that of a passively evolving population that formed the bulk of its stars about 9 Gyr ago. One of the principal advantages of the SDSS sample over previous samples is that the galaxies in it lie in environments ranging from isolation in the field to the dense cores of clusters. The fundamental plane shows that galaxies in dense regions are slightly different from galaxies in less dense regions.