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The Evolution of AGN Obscuration and the X-ray Background

The Evolution of AGN Obscuration and the X-ray Background. Ezequiel Treister (ESO) Meg Urry (Yale) Julian Krolik (JHU) Shanil Virani (Yale ). X-ray Background. XRB well explained using a combination of obscured and unobscured AGN. # w NH > 10 23 cm -2 still uncertain.

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The Evolution of AGN Obscuration and the X-ray Background

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  1. The Evolution of AGN Obscuration and the X-ray Background EzequielTreister (ESO) Meg Urry (Yale) Julian Krolik (JHU) ShanilVirani (Yale)

  2. X-ray Background XRB well explained using a combination of obscured and unobscured AGN. # w NH > 1023 cm-2 still uncertain. The XRB does not constrain the fraction of obscured AGN. • Setti & Woltjer 1989 • Madau et al. 1994 • Comastri et al. 1995 • Gilli et al. 1999,2001 • And others… Treister & Urry, 2005

  3. What do we know so far? • More obscured AGN at low luminosity (Steffen et al. 2003, Ueda et al. 2003, Barger et al. 2005, Akylas et al. 2006) • More obscured AGN at high-z? (Ueda et al. 2003: No, La Franca et al. 2005: yes, Ballantyne et al. 2006: yes) • Problems: • Low number of sources • Selection effects: • - X-ray selection (missed obscured sources) • - Optical incompleteness (no redshifts) • - X-ray classification: “K correction”

  4. Meta-Survey • 7 Surveys, • 2341 AGN, 1229 w Ids • 631 Obscured • (no broad lines) • 1042<Lx<1046, 0<z<5 Treister & Urry, 2006

  5. Total effective area of meta-survey Treister & Urry, 2006

  6. Ratio vs Redshift Treister & Urry, 2006

  7. Ratio vs Redshift Key input: Luminosity dependence of obscured AGN fraction. See also: La Franca et al. 2005 Ballantyne et al. 2006 Akylas et al. 2006 Treister & Urry, 2006

  8. Ratio vs Luminosity Hasinger et al. Treister & Urry, 2006

  9. Luminosity Dependence Evolution Low-z High-z Treister & Urry, 2006

  10. The AGN Unified Model A change in the IR/Bol flux ratio may indicate a change in torus geometry. Urry & Padovani, 1995

  11. Low L • GOODS: North+South fields • 10 unobscured AGN • All Spitzer 24 µm photometry • 8 with GALEX UV data • High L • SDSS DR5 Quasar sample • 11938 quasars, 0.8<z<1.2 • 192 with Spitzer 24 µm photometry • 157 of them with GALEX UV data Torus StructureSample • Completely unobscured AGN • Narrow redshift range, 0.8<z<1.2 • Wide range in luminosity • Data at 24 µm from Spitzer • Mid L • COSMOS • 19 unobscured AGN • 14 Spitzer 24 µm photometry • All with GALEX UV data

  12. Torus Structure Change in 24 µm/Bol ratio with luminosity! • Lower ratio at high L • Consistent with larger opening angles at higher luminosities. Treister et al, ApJ submitted.

  13. Fraction of Obscured AGN Similar luminosity dependence as found on X-ray surveys. • Higher values from • fIR/fbol method. • Obscured AGN • missed by X-ray • surveys. Treister et al, ApJ submitted.

  14. Compton Thick AGN • Defined as obscured sources with NH>1024 cm-2. • Very hard to find (even in X-rays). • Observed locally and needed to explain the X-ray background. • Number density highly uncertain. • High energy (E>10 keV) observations are required to find them.

  15. CT AGN and the XRB X-ray background does not constrain density of CT AGN Treister et al, submitted

  16. Treister & Urry, 2005 CT AGN and the XRB XRB Intensity HEAO-1 +40% Treister et al, submitted

  17. Treister & Urry, 2005 Gilli et al. 2007 CT AGN and the XRB XRB Intensity HEAO-1 Original HEAO-1 +10% HEAO-1 +40% Treister et al, submitted

  18. Treister & Urry, 2005 Gilli et al. 2007 Most likely solution CT AGN Space Density CT AGN and the XRB XRB Intensity HEAO-1 Original HEAO-1 +10% HEAO-1 +40% Treister et al, submitted

  19. Summary • AGN unification can account well for the observed properties of the X-ray background. • The obscured AGN fraction decreases with increasing luminosity. • Ratio of IR to Bolometric luminosity in unobscured AGN suggest this is due to a change in opening angle. • The obscured AGN fraction increases with redshift as (1+z)0.4. • Survey at high energies starts to constrain the spatial density of CT AGN.

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