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AGN IN THE SPITZER ERA: UNVEILING OBSCURED ACCRETION

AGN IN THE SPITZER ERA: UNVEILING OBSCURED ACCRETION. Carlotta Gruppioni (INAF-OABO) Bologna, 8 Giugno 2007. SUMMARY. Why infrared for detecting AGN? - Unobscured AGN - Obscured AGN AGN emission in the infrared “Old’’ results from IRAS & ISO What is Spitzer

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AGN IN THE SPITZER ERA: UNVEILING OBSCURED ACCRETION

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  1. AGN IN THE SPITZER ERA: UNVEILING OBSCURED ACCRETION Carlotta Gruppioni (INAF-OABO) Bologna, 8 Giugno 2007

  2. SUMMARY • Why infrared for detecting AGN? - Unobscured AGN - Obscured AGN • AGN emission in theinfrared • “Old’’ results from IRAS & ISO • What is Spitzer - IR selection techniques for AGN - Recent Results from Spitzer • How many AGN in complete IR samples?

  3. WHY INFRARED? • Infrared explores thehidden Uiverse (obscured by dust) • A large fraction of soft X-ray, UV and optical emission from AGN is absorbed by dust and re-radiated in the infrared (IR)  Sensitive measurements in the IRprovide an opportunity to look for obscured AGN not identified in X-ray and optical surveys

  4. Selection of unobscured AGN Examples: high X/O sources (moderate obscured AGN at z~1-2 hosted in massive ellipticals) BUT: hard X-ray surveys still miss the highly obscured sources(i.e. Compton thick: Nh>1024 cm-2): don‘t sample the XRB peak Most efficient way:Hard X-ray surveys Fiore et al. 2003, A&A Mignoli et al. 2004, A&A Mainieri et al. 2005, A&A Maiolino et al. 2006, A&A Missing population: (numerous) moderately luminous, NH>23, z=0.5-2 AGN(Worsley et al.)

  5. Why should we care about obscured AGN? • Obscured AGN are needed: - to reproduce the X-ray background peak(Setti & Woltjer 1989, Comastri et al. 1995 etc. ) - Unified Models: dusty torus around AGN responsible for absorption of X-ray to NIR nuclear radiation - models predict that AGN activity in the past take place in “dusty” environments/systems • Need to separate AGN from stellar activity to: - Have a complete picture of galaxy(-AGN) formation and (co)evolution  only through a precise census of AGN activity in the Universe it is possible to obtain strong constraints to models for the formation and evolution of structure

  6. AGN emission in the IR unabsorbed The obscured AGN IR Spectral Energy Distribution (SED) is dominated by thermal emission from dust(Neugebauer 1979), heated by the primary optical/UV continuum dominating the unobscured AGN SEDs.  The broadness of the IR SED, which could not be reproduced by means of single-temperature blackbody, was explained in terms of multiple temperature component dust.  According to the AGN Unified Model, the dust is distributed as a (clumpy?) annular ring (torus) around the central BH. • The different orientations of the dusty torus with respect to the line of sight are responsible for the differences observed in the X-rays/optical spectra/SEDs/etc of type 1 and type 2 AGN. absobed

  7. Type 2 AGN Optical emission from Type 2 AGN can be diluted by the host galaxy • difficult to classify as AGN from optical line diagnostics. • Crucial range: near-/mid-infrared (NIR/MIR) where galaxy SEDs have a dip (2-5 m) and the hot dust heated by the AGN start contributing, filling up the dip. flat dusty torus emission dip

  8. Complementary approach: IR colour selection Blue (unobs) Red AGN (unobs and obs) are expected to have warm power-law SEDs at>1 μm (≠ from elliptical/starburst) AGN Red (obs) AGN (both type 1 and 2) can be isolated in NIR/MIR diagrams νSν Blue Red SEVERAL IR colour-selection criteria proposed so far(i.e. Lacy et al. 2005; Stern et al. 2005; Barmby et al. 2006, etc.)  PROBLEMS: Completeness (are all AGN selected?) Reliability (are only AGN selected? How much galaxy “contamination”?) Elliptical Flat/Blue Red Starburst Optical NIR IRAC 3.6 4.5 5.8 8.0 NEEDComplete Multiwavelength Characterization

  9. AGN in the IR: from IRAS to ISO and SPITZER IRAShas explored the local Universe(z < 0.2)in theIR (10 – 200 μm) for the first time, finding that: • The majority of the most luminous galaxies in the Universe emit the bulk of their energy in the far-infrared. They often contain both extreme starbursts and AGN. • Even normal spiral galaxies radiate at least 30% of their energy in the IR (Sanders & Mirabel, 1996, ARA&A, 34, 749) • About 13% of local 12-µm IRAS sources have a Seyfert 1 /Seyfert 2 nucleus (Rush, Malkan & Spinoglio, 1993, ApJS, 89,1)

  10. MIR/FIR emission 4x stronger in the quasars than in the radio galaxies. Do radio galaxies contain potent sources of radiation that are hidden at shorter wavelengths?(Heckman, Chambers & Postman, 1992, ApJ, 391, 39)  • First torus models to reconcile IR observations for type 1 / type 2 AGN with Unified Models (i.e. Pier & Krolik, 1992, ApJ, 401, 99; Granato & Danese, 1994, MNRAS, 268, 235; etc.) :

  11. Solving the Radiative Transfer Equation The equilibrium temperature (and hence thermal emission) of the grains of each species in each sample element is found by solving the thermal equilibrium equation Qabs, Qem = grain absorption/emission efficiency B(λ, Tik) = blackbody emission Tik = temperature of a given grain within the ikth sample element Jik = incoming specific intensity on the volume element For the first iteration: ik (λ) = optical depth between the central source and the ikth element rik = distance At the second iteration, the new incoming radiant flux is:

  12. Infrared Space Observatory ISO (0.65-m Telescope) (> 1000times better sensitivity thanIRAS) has explored for the first time the Universe atz > 0.5in theMIR (15 µm: ISOCAM)  First deep MIR surveys for distant galaxies and AGN

  13. Main ISOCAM results on AGN • ISO SWS Spectroscopy: powerful tool to distinguish star-formation (PAHs) from AGN activity (continuum) (i.e. Laurent et al., 2000, 359, 887) • AGN contribution to MIR surveys derived from: Correlation analysis of deep X-ray and MIR observations (Lockman Hole + HDF-N): AGNs are 15-20% of the MIR population down to 0.05 mJy(Fadda et al., 2002, A&A 383, 838)

  14. Optical Spectroscopy (ELAIS-S1): AGNs (type 1 & 2) account for ∼25% of the MIR sources down to 0.5 mJy. (La Franca et al., 2004, AJ, 127, 3075) • AGN 15 µm Luminosity Function type-1: pure luminosity evolution L(z)=L(0)(1+z)2.9 type-2: L(z)=L(0)(1+z)1.8-2.2 (Matute et al., 2002, AJ, 127, 3075; 2006, MNRAS)

  15. From ISOCAMto Spitzer... Spitzer Telescope (0.85-m) is now providing new insight into the IR population of galaxies and AGN In particular with the MIPS 24-m band, detecting the high-z (z~1.5-3.0) analogs of the 15-m sources

  16. About SPITZER Telescope: 0.85-m launch: August 2003 Mission: 2.5-5 years Wavelength: 3 - 180 m Capability: Imaging/Photometry 3-180 Spectroscopy 5-40 m Spectrophotometry 50-100

  17. SPITZER Measurements - Imaging

  18. SPITZER Measurements - Spectroscopy

  19. Main Results on AGN from Spitzer • IRAC/MIPS colour-colour diagrams are able to isolate unobscured/obscured AGN (i.e. Lacy et al. 2004; Stern et al. 2005; Barmby et al. 2006; Martinez-Sansigre et al. 2005; Fiore et al. 2007) • IRS spectroscopy of MIR objects optically faint (or invisible) able to identify highly obscured AGN at high z (i.e. Houck et al. 2004, 2005; Highdon et al. 2004; Weedman et al. 2006) • Broad-band SED analysis able to identify AGN signature in the MIR (i.e. Alonso-Herrero et al. 2006; Rodighiero et al. 2007; Pozzi et al. 2007; Gruppioni et al. 2007)

  20. Lacy et al., 2004, ApJS 154, 166MIR properties of SDSS quasars (FLS survey) • SDSS quasars(crosses) populate a • well-defined region in the IRAC • colour-colour space – independent • and not consecutives - and have • S(8.0)~1 mJy • Candidate AGN are IRAC sources in the same locus and with S(8.0)>1 mJy • 16SDSS QSO • 16Candidate obscured AGN” • 11not identified/classified • Ratio obs/unobs=1:1 • Reverse argument: • In the same region there are ~2000 • additional sources with S(8.0)<1 mJy!! ~2000 sources

  21. Stern et al. 2005, ApJ, 631, 163MIR properties of AGN in theBootes/AGES survey • Spectroscopically confirmed AGNoccupy a region in the IRAC color-color space - independent • and consecutives colors • Contamination from other objects is very low • Selection effect Bootes/AGES survey probe only z<0.6 galaxies… QUITE SHALLOW (limited mainly to R<19-21) • don’t sample z>0.6 galaxies!

  22. Martinez-Sansigre et al. 2005, Nature 436, 666Selection type-2 AGN at z~2 with Spitzer • S(24 micron) > 300 muJy • sample QSO with L>0.2L* at z=2 • S(3.6 micron) < 45 muJy • remove naked type 1 AGN and low-z type-2 • 350 muJy < S(1.4GHz) < 2 mJy • ensure candidates being radio-quiet QSO rather than SB and filter out radio-loud objects 21candidates 10 spectroscopically confirmed at z=1.4-4.2, with no BL! The remaining areblank spectra (ellipticals??) No evidence for contamination in this sample (but they are looking for specificobjects..)

  23. Fiore et al. 2007, ApJ, submittedUnveiling Obscured Accretion in the Chandra Deep Field South Obscured AGN z=0-4 (Pozzi et al. 2007) • High 24-µm/optical ratio (> 1000) + red colours (R-K > 4.5) • highly obscured AGN at high z • Analysis of the X-ray properties of these extreme sources  most are indeed likely Compton thick AGN Arp 220 z=0-4 Elliptical z=0-4

  24. MIR AGN F24/FR > 1000 R-K > 4.5 F24/FR > 1000 R-K < 4.5 F24/FR < 100 R-K > 4.5

  25. F24µm/FR >1000 R-K>4.5 F(0.3-1.5keV)~10-17 cgs F(1.5-4keV)~10-17 cgs

  26. F24µm/FR <100 R-K>4.5 F(0.3-1.5 keV)~210-17 cgs F(1.5-4 keV) < 510-18 cgs

  27. Highdon et al. 2004, ApJS, 154, 174; Houck et al. 2005, ApJ, 622, L108Spitzer-IRS Spectroscopy of optically obscured MIR sources • Redshifts derived for 24-µm sources that are optically very faint (R > 24.5 mag) from strong silicate absorption feature (@9.7 µm)obscured nuclei at 1.7 < z < 2.8 

  28. Need for Multiwavelength Surveys (+ possibly MIR Spectroscopy !) • Use both X-ray and MIR surveys: • Select unobscured and moderately obscured AGN in X-rays • Add highly obscured AGNs selected in the MIR  • Simple approach: differences are emphasized in a wide-band SED analysis

  29. How to quantify AGN (both obscured and unobscured) versus galaxy fraction in complete / statistical samples? • Study broad-band SEDs and multi-wavelength properties of complete samples (i.e. MIR / X-ray / morphologically selected) with available optical spectroscopy • confirm with MIR spectroscopy

  30. Alonso-Herrero et al. 2006, ApJ 640, 167Infrared power-law galaxies in the CDFS: AGN and ULIRGs • 24 µm sources with power-law emission in the IRAC 3.6-8 µm bands • Those detected in X-rays (50%) have luminosities typical of AGN • Those not detected in X-rays have global X-ray to MIR SED properties that make them good IR bright/X-ray absorbed candidate AGN

  31. Rodighiero, Gruppioni, Civano et al. 2007, MNRAS,376, 416Hidden Activity in High-z Spheroidal Galaxies from MIR and X-ray Observations in the GOODS-N Field 168 morphologically classified(Bundy et al. 2005) spheroidal galaxies in the GOODS-N field: 19 with(unexpected)24 μm detection (12also detected in X-rays) MIR to NIR luminosity ratios in GOODs objects (<z> ≈ 0.7)~10x higherthan in local early-types detected by IRAS(Knapp et al. 1992) No mass loss from evolved giant stars dominating MIR

  32. Broad-band SEDs:MIR in excess with respect to expectations for elliptical galaxies In most cases:SED well fitted byevolved stellar pop (reproducing opt/NIR) +dusty torus heated by AGN (reproducing MIR/FIR)(Fritz et al. 2006) fit with starburst fit with elliptical+torus

  33. Pozzi et al. 2007, A&A, in press, astro-ph/0704.0735 The bolometric output of luminous obscured quasars: The Spitzer perspective 8 obscured AGN candidates at high z selected from hard X-ray survey (high X/O ratio)  Spitzer observations (3.6- 24 µm)  All detected by Spitzer Dust reprocessed by torus And thermally re-emitted

  34. Bolometric Luminosity: 1045 - 1047 erg s-1 Bolometric Correction: ~25 High Stellar Mass: (0.8 - 6) x 1011 M BH Mass: (0.2 - 2.5) x 109 M Eddington Ratio: L/Ledd < 0.1  low accretion rate phase

  35. Gruppioni et al. 2007, ApJ, submittedBroad-band SEDs of a Complete Spectroscopic Sample of MIR Selected Sources at intermediate z 200 MIR sources with spectroscopic z (0.1-1.5) Data from far-UV [0.13 µm] (GALEX) to far-IR [160 µm] (Spitzer)  SED-fitting SED-class compared with spec class QSO Seyfert 2 Data fitted with 21 Template SEDs of IR galaxies/AGN by Polletta et al.(2007)

  36. Example of fits with Galaxy/AGN Templates  SED-fitting able to identify AGN activity in 50% of MIR sources (to 0.5 mJy)

  37. SED-fitting versus spectroscopic classification SED Classification: Spectroscopic Class S0/Sa/Sb/Sc/Sd/Sdm: Galaxy (83) Galaxy (106) M82/NGC6090/Arp220: Starburst (13) Starburst (32) Sey2/Sey1.8/RedQSO/I19254: AGN 2 (73) Liner/AGN 2 (31) QSO/Mrk231: AGN 1 (31) AGN 1 (25) Main differences: SEDs classify more AGN (especially type 2) 2. Many galaxies with only Hα or [OII] emission in their spectra [e(a)] do show AGN-like SEDs

  38. STRONG IMPACT ON EVOLUTIONARY MODELS? AGN/galaxy relative fractions AGN fraction with new classification based on SEDs (UPPER LIMIT?) Matute et al. 2006 model predictions (LOWER LIMIT?) See also Brand et al. 2006 for a 24 μm selected sample

  39. YES: STRONG IMPACT ON EVOLUTIONARY MODELS! Observed Source Counts: Spectroscopic classification SED classification AGN lower limit? AGN upper limit? GAL TOT AGN TOT AGN 2 AGN 1

  40. MAIN MODEL CHANGES: Less objects powered by pure star-formation Less evolution for galaxies (starburst): SEDs evolving with LIR (or z) for all: from S0 to Sd/Sdm for normal galaxies from M82 to ULIG for starbursts • More objects containing an AGN • More evolution for AGN (type 2): • both luminosity and density (more numerous)? • Similar evolution for type 1 AGN (slightly more objects…)

  41. …need for HERSCHEL (3.5-m)? Evolution of dusty galaxies up to: IRAS:  z=0.2 ISOCAM:  z=1.5 SPITZER:  z=3 HERSCHELwill operate in the FIR/sub-mm between75 and 500 μm  SF up to z=4-5

  42. …need for HERSCHEL? Locate the peak of dust emission in High-z AGN/galaxies dust Temperature detailed SEDs in FIR z=2  Better Galaxy/AGN Separation! Obscured AGN Extreme Starburst

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