1. “false-color” 0.5-7 keV X-ray image of the Bootes field A large population of mid-infrared selected, obscured AGN in the Bootes field Ryan C. Hickox Harvard-Smithsonian Center for Astrophysics Extragalactic Surveys Workshop Cambridge, MA 8 November, 2006 Hickox et al. 2006, submitted to ApJ

2. Collaborators Chandra (CfA) C. Jones W. Forman S. Murray A. Kenter R. Narayan Spitzer (JPL/Caltech/CfA) P. Eisenhardt M. Brodwin V. Gorjian D. Stern M. Pahre and the IRAC Shallow Survey Team Optical spectroscopy (OSU/Arizona) K. Kochanek D. Eisenstein R. Cool and the AGES Team Optical photometry (NOAO) B. Januzzi A. Dey K. Brand M. Brown and the NDWFS Team

3. Data from Bootes survey Optical photometry: NOAO DWFS photometry B w,R,I,J,K (Januzzi & Dey 1999) Infrared: Spitzer IRAC Shallow Survey (Eisenhardt et al. 2004) ~30,000 sources are detected in all four IRAC bands. X-ray: Chandra XBootes survey (Murray et al. 2004, Kenter et al. 2005), > 3000 X-ray sources Optical spectroscopy: AGES survey w/ MMT/Hectospec ~2000 broad line AGNs, 80 narrow- line AGNs, and ~20,000 normal galaxies.

4. Multiwavelength studies of AGN (Manners 2002) (Urry & Padovani 1995) BUT, NOT REALLY!

5. Multiwavelength studies of AGN X-rays: ~3000 in Bootes sample Optical/UV ~2000 in sample Infrared: ~2000 in sample (Manners 2002) (Urry & Padovani 1995) Focus on high-z objects: redshifts come from spectroscopic (AGES) or photometric (IRAC + Bw, R, I, Brodwin et al. 2006) estimators. We include objects in the sample with z>0.7

6. Finding obscured AGN (Urry & Padovani 1995) X-rays and infrared are especially useful for identifying OBSCURED (Type 2) AGN, which are predicted from: -> unified models (e.g. Antonucci 1993, Urry & Urry & Padovani 1995) -> merger fueling models (e.g. Hopkins et al. 2006 ) -> cosmic X-ray background synthesis (e.g., Setti & Woljer 1989, Treister et al. 2005, Gilli et al. 2006) Much recent work has studied obscured AGN (e.g. X-ray: Alexander et al. 2005, Mainieri et al. 2005, Treister et al. 2005, Barger et al. 2005, Ptak et al. 2005, optical: Zakamska et al. 2003, infrared: Lacy et al. 2004, Martinez-Sansigre et al. 2005, Polleta et al. 2006, Brown et al. 2006, Alonso-Herrero 2006)

7. Infrared selection of AGN Dust heated by AGN Colder dust/PAHs (Glikman et al. 2005) (Lagache et al. 2004)

8. z=0.3 IRAC bands Infrared selection of AGN

9. z=0.3 Infrared selection of AGN

10. z=0.3 Infrared selection of AGN

11. z=0.3 Infrared selection of AGN

12. z=0.3 Infrared selection of AGN

13. z=0.3 Infrared selection of AGN

14. z=0.3 Infrared selection of AGN

15. Following Stern et al. (2005) See also: e.g., Lacy et al. (2004), Eisenhardt et al. (2004), Alonso-Herrero et al. (2006)

16. Optical/UV vs. IR luminosity ~ L * for z=1 ellipticals (e.g. Ilbert et al. 2006) Constant UV/IR spectral shape Unobscured? IRAGN 1s ~750 objects Obscured? IRAGN 2s ~650 objects Hickox et al. 2006, ApJ submitted

17. Are IRAGN 2s obscured? We test this picture with three predictions: Test 1: X-ray properties of IRAGN 2s should be consistent with absorbed AGNs: high X-ray luminosities, absorbed spectral shapes Test 2: Obscuring dust in the IRAGN 2s should be sufficient to obscure ALL the optical/UV light Test 3: IRAGN 2s should have optical morphologies and colors similar to normal galaxies

18. Test 1: X-ray luminosities Average X-ray fluxes from stacking analysis For both IRAGN 1s, and IRAGN 2s, average L X ~10 43 -10 44 ergs s -1, typical of Seyferts/quasars 2-7 keV 0.5-2 keV 10 44 10 43 10 44 10 43

19. Test 1: X-ray spectral shapes Average X-ray fluxes from stacking analysis Hardness ratio: HR=(HB-SB)/(HB+SB) crude measure of X-ray spectrum HR~-0.5 for IRAGN 1s corresponds to a spectrum typical of Type 1 AGNs (photon index Γ=1.8) HR~-0.2 for IRAGN 2s corresponds to moderate obscuration, N H ~3x10 22 cm -2

20. Test 2: Obscuration by dust For a typical range of gas to dust ratios (e.g., Fall & Pei 1989), for N H =3x10 22 cm -2, τ UV = 2.5-40 So even for the moderate X-ray absorption, the obscuring material can be optically thick in the rest-frame UV for a reasonable dust-to-gas ratio. VLT/ESO

21. Test 3: Optical morphologies of IRAGN IRAGN 2 are galaxy dominated IRAGN 1 are nuclear dominated

22. Test 3: Optical colors of IRAGN templates: elliptical, Sb, quasar IRAGN 2 colors match galaxies IRAGN 1 colors match quasar

23. Are IRAGN 2s obscured? Predictions: Test 1: X-ray properties of IRAGN 2s should be consistent with absorbed AGNs: high X-ray luminosities, absorbed spectral shapes Test 2: Obscuring dust in the IRAGN 2s should be sufficient to obscure ALL the optical/UV light Test 3: IRAGN 2s should have optical morphologies and colors typical of normal galaxies

24. Are IRAGN 2s obscured? Predictions: Test 1: X-ray properties of IRAGN 2s should be consistent with absorbed AGNs: high X-ray luminosities, absorbed spectral shapes YES Test 2: Obscuring dust in the IRAGN 2s should be sufficient to obscure ALL the optical/UV light YES Test 3: IRAGN 2s should have optical morphologies and colors similar to normal galaxies YES

25. Comparison to other obscured AGN samples

26. We have found ~650 candidate obscured AGN at 0.7<z<3. This represents one of the largest populations of luminous, obscured AGN identified to date A few important questions -> How many of these are actually AGN? How many are we missing (i.e. what are the completeness and contamination)? -> Why the bimodality in obscuration at high luminosity? -> What is the underlying number density of distant Type 2 AGN, and their ratio to Type 1 AGNs? -> What are the optical spectral properties of the IRAGN 2s? -> How does this sample overlap with the absorbed AGN from other selection techniques (Chandra Deep Fields, etc.)? unabsorbed Quite extincted Why so few objects?

27. Summary (a poem) Observations in a great wide field of nine whole square degrees Show us thousands upon thousands of new active galaxies We can pick them out with Chandra, or in the optical instead, But we can also use their colors in the Spitzer infrared Our technique selects a lot of broad-line AGN, that's sure But we also find a lot sources that are quite obscured The X-ray, optical and infrared all do agree: This sample has a lot of obscured objects at high z! But are many even more obscured, and missing from our total? And is the distribution in A V really bimodal? Such fascinating questions loom for us in coming days! It’s quite exciting times for all these AGN surveys

28. Test 3: Optical colors of IRAGN

29. Test 1: X-ray luminosities (X-ray non detected) Average X-ray fluxes from stacking analysis 2-7 keV 0.5-2 keV 10 43 10 44 10 43 10 42

30. Test 1: X-ray hardness (X-ray non detected) Average X-ray fluxes from stacking analysis

31. Tests of photo-zs IRAGN 2s

32. Optical spectral templates