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What can we learn about…

The infrared view of obscured AGNs: from Spitzer to Herschel. What can we learn about… The obscured sources responsible for the peak emission of the CXB at ~30 keV (in flux/area, z~1 ) The growth of supermassive black holes through the Hubble time (in intrinsic luminosity, z~2 )

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What can we learn about…

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  1. The infrared view of obscured AGNs: from Spitzer to Herschel What can we learn about… • The obscured sources responsible for the peak emission of the CXB at ~30 keV (in flux/area, z~1) • The growth of supermassive black holes through the Hubble time (in intrinsic luminosity, z~2) David Elbaz (CEA Saclay) based on 2 studies at : • z~1 with D.Alexander, R.R. Chary • z~2 Daddi et al. 07 paper, with Dave Alexander (Durham), Mark Dickinson (NOAO), Roberto Gilli (U. di Bologna), A.Renzini (U. di Padova) David Elbaz - IR view of AGNs 1

  2. 7.7m 7m Central engine 800pc Dusty torus 100pc Laurent et al. 01 Unified scenario: Compton Thick AGNs = edge-on dusty torusCan IR surveys reveal the missing AGN population unidentified in X-ray ? • nearest radio galaxy, 3.5 Mpc • Unified scenario: dust obscuration depends on the orientation only. David Elbaz - IR view of AGNs 2

  3. Tran et al. (2001) IR signature of the presence of an AGN LIR Star formation AGN LIR<2.5x1012 L: ~82-94% ~6-18% LIR>2.5x1012 L: ~45-55% ~45-55% David Elbaz - IR view of AGNs 3

  4. LIR LIR L15 L7 Infrared properties of local star forming galaxies Correlations between mid and far IR used to derive Lbol, hence SFR. Far IR view of the Universe strongly affected by confusion due to large PSF -> use of mid IR David Elbaz - IR view of AGNs 4

  5. NGC1068 obscured AGNs Compton thin unobscured AGNs Vignati et al. (1999) NGC6240 Compton Thick AGNs 20-30% of the CXB due to Compton Thick AGNsmost of which remain unidentified… What can we learn from the IR ? CT AGNs present a mid IR excess. can IR surveys identify the missing AGNs ? David Elbaz - IR view of AGNs 5

  6. ISOCAM - 15 m 24 m GOODS : Great Observatories Origins Deep Survey (PI Dickinson) Spitzer-IRAC & MIPS 10’ x 15’ 50 % complete @30 mJy 70 % complete @70 mJy 15' 10' =10 comoving-Mpc at z=1 David Elbaz - IR view of AGNs 6

  7. BzK selection: massive galaxies at 1.4 < z 2.5 (Daddi et al. 04) Sample of 1200 BzK selected galaxies in GOODS-S (down to K=22 Vega) David Elbaz - IR view of AGNs 7

  8. Yun, Reddy & Condon 2001 Radio & UV corrected for extinction -> same LIR= consistent with star formation origin David Elbaz - IR view of AGNs 8

  9. Stacked Luminous objects at 8 m, z~2 present a mid infrared excess inconsistent with a star formation origin… David Elbaz - IR view of AGNs 9

  10. Spitzer 70 m SCUBA 850 m Luminous objects at 8 m, z~2 present a mid infrared excess inconsistent with a star formation origin… David Elbaz - IR view of AGNs 10

  11. X-ray stacking analysis (by Dave Alexander) in GOODS-S to K=22 (Vega) Normal galaxies MIR excess gals mid-IR excess sources are much harder than normal ones N.B.: all direct X-ray detections and power law sources are excluded David Elbaz - IR view of AGNs 11

  12. Sub-band stacking with Chandra reveals a shape that strongly supports NH~1024 cm-2 or perhaps more, i.e. Compton Thick At 0.5-2 keV: 2 populations identical consistent with star formation origin with similar SFRs David Elbaz - IR view of AGNs 12

  13. Sub-band stacking with Chandra => Compton Thick AGNs Subtracting power-law from SF --> remarkably similar to AGN template with NH = 3x1024 cm-2 dashed line: AGN SED from Gilli et al 07 including 6.7 keV Fe line and for the z distribution of the sample. David Elbaz - IR view of AGNs 13

  14. GOODS ultra-deep mid IR survey can detect NGC 1068-like CT AGNs to z~2Chandra only to z~0.5 even with 2 mega-seconds ! GOODS zmaxIR ≈ 2 zmaxX-ray ≈ 0.5 David Elbaz - IR view of AGNs 14

  15. obscured AGNs Compton thin unobscured AGNs Compton Thick AGNs Contribution to the Cosmic X-ray Background • About 20-30% of the 10-30 keV background is due to unidentified CT AGNs (Gilli et al. 07) • CT AGNs with mid IR excess at z~2 = 3200 objects/deg2 produce 10-25 % of the missing hard X-ray background Most of the missing background comes from similar sources but at z~1 • (negligible contribution to the 2-8 keV band) David Elbaz - IR view of AGNs 15

  16. SB N1068 Stacking : F(70m)= 1.50±0.18 mJy (2 level without stacking) Spitzer 24 m sources at z~1 anomalously faint at 70 m NGC 1068 (Le Floc'h et al. 01: ~70% MIR from AGN) X-ray Stacking: hard src ~ 20 Compton Thick AGNs ! (X-ray unselected as AGNs) -> 720/sq.deg. <-> 2800/sq.deg. required to produce the X-ray bkg (Worsley et al. 05) ≠ radio excess X-ray undetected AGNs ( Donley, Rieke et al. 06)… David Elbaz - IR view of AGNs 16

  17. Contribution to black hole growth : z~2 z~1 mid IR excess CT AGNs = 25% of massive galaxies -> Today: MBH~2 [-1.5,+2]x10-3M* -> substantial contribution of these AGNs to BH growth in massive galaxies (M*~3-4x1010M) Models from Gilli et al 2007 The census of Compton Thick AGNs Contribution of mid IR excess sources to the volume density of C.T. AGNs : at z~2: consistent with 100 % of CT AGNs with LX>1042 erg s-1 at z~1: consistent with 25 % of AGNs producing the CXB and 100 % of CT AGNs with LX>3x1042 erg s-1 David Elbaz - IR view of AGNs 17

  18. Discussion & conclusions • Spitzer and soon Herschel are efficient at detecting Compton Thick AGNs missed in X-ray surveys. • These "mid IR excess Compton Thick AGNs", confirmed from X-ray stacking, potentially represent a large fraction of the BH growth, but resolve at present ~25% of the CXB assuming model extrapolation to 30keV. • Official Herschel sensitivity limits will only marginally improve this result but actual expectations may do much better. David Elbaz - IR view of AGNs 18

  19. Discussion & conclusions • Spitzer and soon Herschel are efficient at detecting Compton Thick AGNs missed in X-ray surveys. • These "mid IR excess Compton Thick AGNs", confirmed from X-ray stacking, potentially represent a large fraction of the BH growth, but resolve at present ~25% of the CXB assuming model extrapolation to 30keV. • Official Herschel sensitivity limits will only marginally improve this result but actual expectations may do much better. • This population is at the level of : 2x10-2Crab at z~1 and 5x10-3Crab at z~2 = 25 & 100 times fainter than expected SIMBOL X depth (~0.5 Crab~3x10-14 erg s-1 cm-2 at 10-40 keV) or 2.5 & 10 times fainter if ~3x10-15 erg s-1 cm-2 is reached David Elbaz - IR view of AGNs 19

  20. NGC 1068 CIII HeII 24m excess CIV Ly HeII CIII CIII HeII SiIV 24m /UV OK No optical spectral lines typical of hidden AGNs (GMASS deep spectra; C. Halliday et al) [CIII]1909 (EW~1-2A) similar to star forming galaxies [HeII]1640 very faint David Elbaz - IR view of AGNs 20

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