Quasar Selection

1
Quasar Selection
2
High-z Quality Cuts

• Throw out measurements that
• Are saturated
• Are on the edge of a chip/frame
• Are on chips 26A or 26C
• Have a bad PSF flux fit
• Have I, z1, or z2 ?2 gt10
• Have I, z1, or z2 PSF-Aperture 0 gt 2 mags
• Throw out objects that
• Have close neighbors
• Are near a bright star
• Have I S/N lt 3
• Have z S/N lt 2

3
High-z Color Cuts

• Require
• R - I gt 3
• B - I gt 3
• I - z gt 2.2
• r - z gt 2.2
• Also require
• I gt 18.5
• z gt 18.5

4
Cut Selection Method

• Have been using completeness and purity plots
• Only count a detection if its colors are measured
  roughly well enough for the color selection
• For high z, require Quest i-z gt SDSS i-z
• For lower z, require Quest r-i and i-z to agree
  with SDSS to within 0.2 mags
• Need to do this again with the newest extinctions
  zero points.

5
Johnson Color-Redshift
6
Gunn Color-Redshift
7
Variability?

• Combined with color cuts?
• Need to do more careful data selection