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AGN9, Ferrara, 24-27 maggio 2010 New insights on the torus models from high-resolution SEDs of obscured high-z QSOs Margherita Bonzini Collaborators: M.

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Presentation on theme: "AGN9, Ferrara, 24-27 maggio 2010 New insights on the torus models from high-resolution SEDs of obscured high-z QSOs Margherita Bonzini Collaborators: M."— Presentation transcript:

1 AGN9, Ferrara, maggio 2010 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 (Cornell University, USA), L. Sargryan (Byurakan Astrphysical Observatory, Armenia), G. Lodato (Università degli studi di Milano)

2 AGN9, Ferrara, maggio 2010 Outline Margherita Bonzini Obscured Active Galactic Nuclei (AGN) at high redshift Sample and data Analysis: -estimate of the host galaxy and AGN spectral energy distributions (SEDs) -fit of the AGN SED with clumpy and smooth torus models Main results

3 AGN9, Ferrara, maggio 2010 Obscured Active Galactic Nucleai Margherita Bonzini Black hole and accretion disk (optical-UV, X) Anisotropical dust structure (TORUS) (Infrared; IR) (e.g. Krolik & Begelman, 1988; Antonucci 1993) Unobscured AGN Obscured AGN

4 AGN9, Ferrara, maggio 2010 Obscured high-z AGN Margherita Bonzini Some observational problems: 1.Faint at optical and X-ray wavelengths 2.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? 1.To estimate the contribution to the total energy due to accretion processes 2.To study AGN evolution 3.To investigate the AGN and host galaxy interplay

5 AGN9, Ferrara, maggio 2010 Sample selection Margherita Bonzini SELECTION CRITERIA: F24 μm > 0.8 mJy F[24 μm] /F[R] > 1000 Obscured quasars at z 2 (Weedman et al. 2006; Dey et al. 2008; Polletta et al. 2008) With HST data ( Bussmann et al. 2009, ApJ, 639, 750) + HST images 30 sources From the Spitzer survey of the Boötes field ( 8 deg 2 )

6 AGN9, Ferrara, maggio 2010 Objectives and method Margherita Bonzini 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

7 AGN9, Ferrara, maggio 2010 Spitzer/IRS spectra Margherita Bonzini 10μm silicate feature in ABSORPTION Mean redshift: 2.17 ± 0.36

8 AGN9, Ferrara, maggio 2010 Spectral energy distribution (SED) Margherita Bonzini Host Galaxy AGN 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) Separation of the host galaxy and AGN contribution to the total flux High-resolution HST data Total Flux

9 AGN9, Ferrara, maggio 2010 Host galaxy and AGN contribution Margherita Bonzini 1.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 2.Host galaxy subtraction from the total flux AGN SED The UV nuclear emission is absorbed by the dust and thermally re-emitted in the IR Total Flux Host Galaxy AGN

10 AGN9, Ferrara, maggio 2010 Comparison with high-resolution MIR SEDs of local Seyfert 2 galaxies Margherita Bonzini (Ramos Almeida et al., 2009) 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

11 AGN9, Ferrara, maggio 2010 Torus models Margherita Bonzini The dust is organized in clumps distributed in a toroidal structure around the black hole (Krolik & Begelman, 1988). CLUMPY tori (Nenkova et al., 2008) SMOOTH tori (Granato & Danese, 1994) Φ ~ 1Φ 1 TWO SETS OF TORUS MODELS Φ = V c /V tot

12 AGN9, Ferrara, maggio 2010 SEDs library Margherita Bonzini CLUMPY toriSMOOTH 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. UV-to-IR SEDs with 2 components: 1.Primary nuclear emission (transmitted and reflected) 2.Dust thermal emission

13 AGN9, Ferrara, maggio 2010 Comparison between best-fit models Margherita Bonzini CLUMPY models are NOT able to reproduce the silicate absorption Smooth models better fit obscured QSO SEDs SMOOTH models reproduce continuum + silicate absorption SMOOTH tori CLUMPY tori

14 AGN9, Ferrara, maggio 2010 SMOOTH tori parameters distributions Margherita Bonzini NO constraints on geometrical parameters Optically thick structures along the line of sight

15 AGN9, Ferrara, maggio 2010 Torus size Margherita Bonzini 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)

16 AGN9, Ferrara, maggio 2010 Summary Margherita Bonzini 1.Selection of a sample of obscured quasar at z ~ 2 2.UV-to-MIR SED reconstruction using spectroscopic photometric measurements ( with low and high resolution ) 3.Estimate of the host galaxy contribution using high spatial resolution HST data 4.Characterization of the AGN SED with smooth and clumpy torus models

17 AGN9, Ferrara, maggio 2010 Conclusions Margherita Bonzini 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

18 AGN9, Ferrara, maggio 2010 Margherita Bonzini

19 AGN9, Ferrara, maggio 2010 Margherita Bonzini

20 AGN9, Ferrara, maggio 2010 Conclusions Margherita Bonzini 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

21 IMPRS workshop, Garching, Feb 9-11, 2010 Margherita Bonzini Obscured AGN at high redshift and luminosity The fraction of obscured AGN decreases at high luminosities (from>80% at L~10 42 erg/s to 38% at 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) Dust properties vs luminosity Test of current torus models 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 )

22 IMPRS workshop, Garching, Feb 9-11, 2010 Fitting the AGN SED Nenkova et al., 2002Granato & Danese, 1994 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 Margherita Bonzini OUTPUT: Best fit values and probability distribution of the model parameters (See also e.g. Efstathiou & Rowan-Robinson 1995; van Bemmel & Dullemond 2003; Hönig et al. 2006) N = number of detections F i = fluxes

23 IMPRS workshop, Garching, Feb 9-11, 2010 Fitting results (1): MIR continuum & Si (10 μm) feature Nenkova et al. Margherita Bonzini Granato & Danese

24 IMPRS workshop, Garching, Feb 9-11, 2010 Fitting results (2) Margherita Bonzini Granato & Danese Nenkova et al.

25 IMPRS workshop, Garching, Feb 9-11, 2010 Granato & Danese best-fit parameters Margherita Bonzini About 2/3 of the objects require highly inclined tori with high optical depth


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