New insights on the torus models from high-resolution SEDs of obscured high-z QSOs

1. New insights on the torus models from high-resolution SEDs of obscured high-z QSOs Margherita Bonzini Collaborators: M. Polletta (INAF-IASF Milano), D. Weedman (CornellUniversity, USA), L. Sargryan (ByurakanAstrphysicalObservatory, Armenia), G. Lodato (Universitàdeglistudidi Milano)

2. Outline • Obscured Active Galactic Nuclei (AGN) at high redshift • Sample and data • Analysis: • estimate of the host galaxy and AGNspectral energy distributions (SEDs) • fit of the AGN SED with clumpy and smooth torus models • Main results MargheritaBonzini

3. Obscured high-z AGN Some observational problems: Faint at optical and X-ray wavelengths The obscured AGN fraction decreases with increasing luminosity (?) (e.g. Simpson 2005, Akylas et al. 2006, Maiolino et al. 2007) Recently discovered by the Spitzer Space Telescope (e.g. Weedman et al., 2006; Lacy et al., 2007; Fiore et al., 2008; Polletta et al.,2008) Why studying them? To estimate the contribution to the total energy due to accretion processes To study AGN evolution To investigate the AGN and host galaxy interplay MargheritaBonzini

4. Sample selection From the Spitzer survey of the Boötes field (∼ 8 deg2) • SELECTION CRITERIA: • F24 μm > 0.8 mJy • F[24 μm] /F[R] > 1000 With HST data Obscured quasars at z ∼ 2 (Weedman et al. 2006; Dey et al. 2008; Polletta et al. 2008) + HST images 30 sources (Bussmann et al. 2009, ApJ, 639, 750) MargheritaBonzini

5. Objectives and method • Objectives: • characterization of the nuclear emission of z~2 quasars • dust distribution: • is it organized in a torus? • is it described by current models? • do dust properties vary with redshift and luminosity? • Methods: • nuclear and host galaxy optical-to-MIR SED reconstruction using photometric and spectroscopic data • model comparison MargheritaBonzini

6. Spitzer/IRS spectra Mean redshift: 2.17 ± 0.36 10μm silicate feature in ABSORPTION MargheritaBonzini

7. Spectral energy distribution (SED) • MIPS (24μm) • IRS spectra (8-35μm ) • IRAC (3.6, 4.5, 5.8, 8μm) • HST (I, V, H) • KPNO (Bw, R, I) • (Ashby et al., 2009; Bussmann et al., 2009) Total Flux Host Galaxy AGN High-resolution HST data Separation of the host galaxyand AGN contribution to the total flux MargheritaBonzini

8. Host galaxy and AGN contribution Estimate of the host galaxy SED using a starburst model library (Siebenmorgen & Krügel, 2007) CRITERIA: - agreements with HST data - model < total flux at all λ Host galaxy subtraction from the total flux Total Flux Host Galaxy AGN AGN SED The UV nuclear emission is absorbed by the dust and thermally re-emitted in the IR MargheritaBonzini

9. Comparison with high-resolution MIR SEDs of local Seyfert 2 galaxies NGC 5506 Mrk 573 Circinus NGC 5506 Mrk 573 Circinus NGC 5506 Mrk 573 Circinus NGC 5506 Mrk 573 Circinus The nuclear emission from obscured AGNs with different L and z is similar (Ramos Almeida et al., 2009) MargheritaBonzini

10. Torus models The dust is organized in clumps distributed in a toroidal structure around the black hole (Krolik & Begelman, 1988). TWO SETS OF TORUS MODELS SMOOTH tori (Granato & Danese, 1994) CLUMPY tori (Nenkova et al., 2008) Φ ~ 1 Φ ≪1 Φ = Vc/Vtot MargheritaBonzini

11. SEDs library UV-to-IR SEDs with 2 components: Primary nuclear emission (transmitted and reflected) Dust thermal emission SMOOTH tori CLUMPY tori • 7 PARAMETERS: • dust grains properties • spatial dust distribution • optical depth • inclination angle • 6 PARAMETERS: • number of clouds • spatial dust distribution • optical depth • inclination angle Models are obtained solving the radiative transfer equations. MargheritaBonzini

12. Comparison between best-fit models SMOOTH tori CLUMPY tori SMOOTH models reproduce continuum + silicate absorption CLUMPY models are NOT able to reproduce the silicate absorption Smooth modelsbetter fit obscured QSO SEDs MargheritaBonzini

13. SMOOTH tori parameters distributions Optically thick structures along the line of sight NO constraints on geometrical parameters MargheritaBonzini

14. Torus size Smooth torus models with a deep Si absorption correspond to spatially extended structures (~100 pc ). BUT: high-resolution measurements suggest compact structures (≲ 10 pc ) ( e.g. Tristram et al. 2007; Meisenheimer et al. 2007) Possible explanation: compact torus + cold dust absorber (see also Polletta et al. 2008, Martinez-Sansigre et al 2009) MargheritaBonzini

15. Conclusions • IR continuum: • similar in AGNs with different z and L • well reproduced by both smooth and clumpy torus models • Si absorption: • Not reproduced by clumpy torus models but only by the smooth ones • Importance of using both photometric and spectroscopic data to describe optical-to-IR AGN SEDs • Smooth dust density structures better fit obscured QSO SEDs • Deep Si absorption features correspond to extended structures (in contrast with high resolution measurements) • Possible cold dust component separated from the torus MargheritaBonzini

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18. Conclusions • The IR continuum of AGNs with different z and L is similar • The clumpy model are not able to reproduce the deep Si absorption observed • The SEDs are well reproduced by smooth tori • Deep Si absorptions correspond to extended structures (in contrast with high resolution measurements) • Possible cold dust component separated from the torus • Importance of using both photometric and spectroscopic data to describe optical-to-IR AGN SEDs MargheritaBonzini

19. Obscured AGN at high redshift and luminosity The fraction of obscured AGN decreases at high luminosities (from>80% at L~1042 erg/s to 38% at 1045 erg/s) (e.g. Hasinger et al. 2004, Simpson 2005, La Franca et al. 2005, Treister &Urry 2006, Akylas et al. 2006, Tozzi et al. 2006, Maiolino et al. 2007) Many high-z obscured quasars have been recently discovered by the Spitzer Space Telescope (e.g. Weedman et al., 2006; Lacy et al., 2007; Polletta et al.,2008) • Dust properties vs luminosity • Test of current torus models Margherita Bonzini

20. Fitting the AGN SED Granato & Danese, 1994 Nenkova et al., 2002 METHOD: Minimization of the merit function: METHOD: BayesCLUMPY = code for the Bayesian analysis of AGN SEDs using clumpy models. (Asensio Ramos & Ramos Almeida, 2009, ApJ, 696, 2075) OUTPUT: probability distribution of the model parameters N = number of detections Fi= fluxes OUTPUT: Best fit values and probability distribution of the model parameters (See also e.g. Efstathiou & Rowan-Robinson 1995; vanBemmel & Dullemond 2003; Hönig et al. 2006) Margherita Bonzini

21. Fitting results (1): MIR continuum & Si (10 μm) feature Granato & Danese Nenkova et al. Margherita Bonzini

22. Fitting results (2) Granato & Danese Nenkova et al. Margherita Bonzini

23. Granato & Danese best-fit parameters About 2/3 of the objects require highly inclined tori with high optical depth Margherita Bonzini