CfCP SDSS Science Center Projects

Large-scale Structure

  With our SDSS colleagues, we are measuring the clustering of galaxies in the SDSS redshift survey. Preliminary results based on a sample of 30,000 galaxies were published in 2001. In 2002, we are analyzing a much larger sample of 170,000 galaxies, which enables us to measure how galaxy clustering varies with properties such as luminosity, color, and spectral type. These variations probe the nature of bias, the relation between galaxy and mass clustering. The redshift distortions of the clustering will enable us to measure the cosmic density parameter. In addition, a much larger sample of ~10 million galaxies with photometric redshift estimates is being analyzed, yielding results consistent with those from the redshift survey. We are also working on interpreting these clustering results using the halo occupation model of galaxy formation.

  A catalog of galaxy groups and clusters in the SDSS redshift survey is being constructed, using a friends-of-friends algorithm, which will provide an independent probe of the halo model and cosmological parameters.

Weak Lensing

  We are analyzing galaxy-galaxy lensing in the SDSS imaging data and using it to probe the nature of galaxy dark halos and the correlation of halo properties with the luminous components (morphology, luminosity, etc) of galaxies. Galaxy-galaxy lensing offers a sensitive probe of the cosmic density parameter and a constraint on the bias between mass and light. Preliminary results from SDSS commissioning data were published in 1999; a sample ten times larger is now being analyzed. More information here.

  Statistical weak lensing of clusters detected in the SDSS imaging survey is being used to probe the relation between cluster mass and other observables such as X-ray temperature and the number of cluster galaxies.

Strong Lensing

  We are carrying out a systematic search for lensed quasars in SDSS data, using the ARC 3.5m telescope, Magellan, Keck, and the MMT for follow-up spectroscopy and imaging, with the aim of constructing a homogeneous sample for studies of cosmology and (lens) galaxy properties. So far, several SDSS lenses have been discovered.

Quasars

  We have constructed a spectral classification system for SDSS quasars based on Principal Component Analysis.

Spectroscopic Pipeline

  We have developed the spectroscopic pipeline which processes SDSS spectra, classifies objects, calculates their redshifts, and measures a variety of properties (line equivalent widths, velocity dispersions, spectral classes, etc). We are currently developing techniques to decompose spectra into their components when the light from two objects is found in a single spectroscopic fiber.

Visualization

  We have developed an advanced 3-d visualization tool for viewing the SDSS redshift data (and other multi-dimensional datasets). This system, developed for both scientific and educational outreach purposes, is particularly useful for viewing the large-scale clustering of galaxies and quasars. This system has been on temporary display at the Adler Planetarium and has been featured in Discover magazine, National Geographic, WTTW Channel 11, and WBBM-TV in Chicago.