Redshift

• Not possible from X-ray alone
• Association with multi-λ: not trivial
• NWAY – association with mag/color information
• Redshift estimation
• spec-z: expensive
• photo-z: hard for AGN –> M. Salvato, LT. Hsu
• How much to trust & when not to trust a z
• z with uncertainties, propagate
• include sources w/o redshift