Getting started running SQL on SDSS

Learn about "Structured Query Language" tools.
• Find some high redshift quasars by running a query as follows:
  • -- Go to the SDSS DR7 SQL server, where we will run a query to identify a set of distant quasars. Click on http://cas.sdss.org/dr7/en/tools/search/sql.asp
  • -- Read the "Please Note" at the top of this page. The query we've selected won't stretch the system, but please follow the rules if you try one on your own!
  • -- Erase the words written in the white window and replace them with the following query; set the output format to HTML.
    

    SELECT
      p.ra, p.dec, s.z, p.petroMag_r,
      p.petroR90_r, p.lnLExp_r, p.lnLDeV_r, p.expAB_r, p.isoPhi_r
    FROM PhotoObj p, SpecObj s, SpecLine l
    WHERE
      p.SpecObjID = s.SpecObjID AND
      p.SpecObjID = l.specobjID AND
      l.lineID = dbo.fSpecLineNames('CIV_1549') AND
      p.ra >= 120 AND p.ra <= 150 AND
      p.dec >= 5 AND p.dec <=10 AND
      s.z >= 5.0
    order by p.ra
    

    This will run for a short time. It should return you exactly 4 objects.

  • Understand the criteria that are being used by this query to identify objects in the database. This will require you to explore the syntax of the query --- but it should be pretty obvious!

  • Check out the DR7 Navigator and Explore Tools (http://cas.sdss.org/dr7/en/tools/chart/navi.asp) to investigate the image and spectrum of each object. Learn to use those tools to examine the images and spectra of the quasars found above.

• Check out these sample queries used by your friends in the Cornell EGG. Understand for yourself what they do.

  *************
  Select a set of inclined disk galaxies by H-alpha redshift
  SELECT
    p.ra, p.dec, s.z, p.expAB_r, p.fiberMag_r, p.petroMag_r, 
    p.petroR90_r, p.lnLExp_r, p.lnLDeV_r, l.sigma, l.sigmaErr, 
    l.ew, l.ewErr, l.chisq, l.nu, s.zWarning, p.isoPhi_u, 
    p.isoPhi_g, p.isoPhi_r, p.isoPhi_i, p.isoPhi_z
  FROM PhotoObj p, SpecObj s, SpecLine l
  WHERE 
    p.SpecObjID = s.SpecObjID AND
    p.SpecObjID = l.specobjID AND
    s.specClass=2 AND
    l.sigma >= 2.1897 AND l.sigma <= 15.3280 AND
    p.lnLExp_r > (13.81+p.lnLDeV_r) AND
    l.lineID = dbo.fSpecLineNames('Ha_6565') AND
    (p.ra >= 345 OR p.ra <= 45 ) AND
    p.dec >= 5 AND p.dec <=35 AND
    s.z <= 0.003
  order by p.lnLExp_r desc
  
  **********
  
  Select by velocity dispersion:
  
  SELECT
    p.ra, p.dec, s.z, p.expAB_r, p.petroMag_r,
    p.petroR90_r, p.lnLExp_r, p.lnLDeV_r, l.sigma, l.sigmaErr,
    l.ew, l.ewErr, l.chisq, l.nu, s.zWarning, p.isoPhi_r, p.isoPhi_i
  FROM PhotoObj p, SpecObj s, SpecLine l
  WHERE
    p.SpecObjID = s.SpecObjID AND
    p.SpecObjID = l.specobjID AND
    s.eClass < 0 AND
    p.fracDev_r > 0.8 AND
    l.lineID = dbo.fSpecLineNames('H_3970') AND
    l.sigma*300000.0/l.wave > 350 AND
    (p.ra >= 170 AND p.ra <= 210 ) AND
    p.dec >= 5 AND p.dec <=15 AND
    s.z <= 0.03
  order by p.ra
  
  Notice that sigma is expressed in weird units. To convert
  to km/s you multiply by c and divide by the rest wavelength.
  See the expression above.
  
  ************
  
  Note that the SDSS folks use "weird" wavelength units.
  
  Go to the Schema Browser;
  Search for "wavelength";
  Click on Columns, table SpecLineAll, Line rest wavelength
  Scoll down to "lineID" and click there on "i";