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Tutorial: Position and Magnitude Limited Catalog Query

This procedure outlines how to search the SDSS data for galaxies around an RA and DEC position of a certain r magnitude range and get back the semi-major axis value in each SDSS color.

  1. Access the SDSS Imaging Query Server (IQS)
  2. Set "Limit number of output rows" parameter by estimating the number that you expect (or leave it blank).
  3. Select the parameters to be returned by ctrl-clicking:
    1. minimal - full id info
    2. radec - position info
    3. model_mags - SDSS filter magnitudes
    4. iso_a_g, iso_a_r, iso_a_i, iso_a_z, iso_a_u - semi-major axis measurements
  4. Click the Best radio button to search the database containing the most recent data and reductions
  5. No spectroscopy parameters are necessary for this search.
  6. Select the u, g, r, i, and z radio buttons.
  7. Select "Cone Search" under "Position Constraints"
  8. Enter the raCenter (decimal degrees), decCenter (decimal degrees) and then the radius of your search area in arcminutes (max = 30 arcmin).
  9. Enter the r magnitude range (min and max) to which you wish to limit the search
  10. Ensure that only the "extended Sources (Galaxies)" check box is checked in "Object Type"
  11. For now, use default "ignore" under objc_flags and objc_flags2, but be sure to read about image processing flags and filter your data to obtain meaningful results from the imaging catalogs.
  12. Click on the "Submit Request" button.

Sample Query Response Time

For a query using ra = 120, dec = 40, radius = 30 arcminutes, r model magnitude range 17 - 17.1, and number of rows set at 500:

  • 41 rows returned
  • 50 seconds of real time elapsed

Last modified: Tue Jul 26 20:45:50 CDT 2005