1. G. Lodato (Università degli studi di Milano)
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)
AGN9, Ferrara, maggio 2010

2. Outline 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
AGN9, Ferrara, maggio 2010
Margherita Bonzini

3. Obscured Active Galactic Nucleai
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
AGN9, Ferrara, maggio 2010
Margherita Bonzini

4. Obscured high-z AGN Why studying them? 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
AGN9, Ferrara, maggio 2010
Margherita Bonzini

5. Sample selection Obscured quasars at z ∼ 2 + HST images 30 sources
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
(Bussmann et al. 2009, ApJ, 639, 750)
Obscured quasars at z ∼ 2
(Weedman et al. 2006; Dey et al. 2008; Polletta et al. 2008) +
HST images
30 sources
AGN9, Ferrara, maggio 2010
Margherita Bonzini

6. 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
AGN9, Ferrara, maggio 2010
Margherita Bonzini

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

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

9. 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
AGN9, Ferrara, maggio 2010
Margherita Bonzini

10. Comparison with high-resolution MIR SEDs of local Seyfert 2 galaxies
NGC 5506
Mrk 573
Circinus
NGC 5506
Mrk 573
Circinus
The nuclear emission from obscured AGNs with different L and z is similar
NGC 5506
Mrk 573
Circinus
NGC 5506
Mrk 573
Circinus
(Ramos Almeida et al., 2009)
AGN9, Ferrara, maggio 2010
Margherita Bonzini

11. TWO SETS OF 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
CLUMPY tori
(Nenkova et al., 2008)
SMOOTH tori
(Granato & Danese, 1994)
Φ ~ 1
Φ ≪1
Φ = Vc/Vtot
AGN9, Ferrara, maggio 2010
Margherita Bonzini

12. Models are obtained solving the radiative transfer equations.
SEDs library
UV-to-IR SEDs with 2 components:
Primary nuclear emission (transmitted and reflected)
Dust thermal emission
CLUMPY tori
SMOOTH tori
7 PARAMETERS:
dust grains properties
spatial dust distribution
optical depth
inclination angle
6 PARAMETERS:
number of clouds
Models are obtained solving the radiative transfer equations.
AGN9, Ferrara, maggio 2010
Margherita Bonzini

13. 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 models better fit obscured QSO SEDs
AGN9, Ferrara, maggio 2010
Margherita Bonzini

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

15. Torus size Possible explanation: compact torus + cold dust absorber
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)
AGN9, Ferrara, maggio 2010
Margherita Bonzini

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

17. Possible cold dust component separated from the torus
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
AGN9, Ferrara, maggio 2010
Margherita Bonzini

18. AGN9, Ferrara, maggio 2010
Margherita Bonzini

19. AGN9, Ferrara, maggio 2010
Margherita Bonzini

20. 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
AGN9, Ferrara, maggio 2010
Margherita Bonzini

21. 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
IMPRS workshop, Garching, Feb 9-11, 2010
Margherita Bonzini

22. 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; van Bemmel & Dullemond 2003; Hönig et al. 2006)
IMPRS workshop, Garching, Feb 9-11, 2010
Margherita Bonzini

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

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

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