Problem

• Surveys: >50% of found AGN are obscured
• Intrinsically: most accretion hidden behind layers of gas & dust
• Need selection which is
• not as affected by obscuration
• selection bias can be easily quantified
• Our approach: X-ray selection
• Efficient: most point sources in deep fields are AGN
• Clean: Virtually no galaxy emission at z>0
• Less affected: Hard X-rays pass through obscurer
• Intrinsic luminosity and obscuration measurable from spectrum