agn9, ferrara, 24-27 maggio 2010 new insights on the torus models from high-resolution seds of...

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. Polletta (INAF-IASF Milano), D. Weedman (Cornell University, USA), L. Sargryan (Byurakan Astrphysical Observatory, Armenia) ,

G. Lodato (Università degli studi di Milano)


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


Obscured high-z AGN

Margherita Bonzini

Some observational problems:1. Faint at optical and X-ray wavelengths2. 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?3. To estimate the contribution to the total energy due to

accretion processes4. To study AGN evolution5. To investigate the AGN and host galaxy interplay


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 deg2)


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


Spitzer/IRS spectra

Margherita Bonzini

10μm silicate feature in ABSORPTION

Mean redshift: 2.17 ± 0.36


Spectral energy distribution (SED)

Margherita Bonzini

Host GalaxyAGN

• 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


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 GalaxyAGN


Comparison with high-resolution MIR SEDs of local Seyfert 2 galaxies

Margherita Bonzini

(Ramos Almeida et al., 2009)

NGC 5506Mrk 573Circinus




The nuclear emission from obscured AGNs with different L and z is similar


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 ~ 1 Φ ≪1

TWO SETS OF TORUS MODELS

Φ = Vc/Vtot


SEDs library

Margherita Bonzini

CLUMPY tori SMOOTH 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


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


SMOOTH tori parameters distributions

Margherita Bonzini

NO constraints on geometrical parameters

Optically thick structures along the line of sight


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)


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

AGN9, Ferrara, 24-27 maggio 2010 Margherita Bonzini


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

Margherita BonziniIMPRS workshop, Garching, Feb 9-11, 2010

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)

• 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)

IMPRS workshop, Garching, Feb 9-11, 2010

Fitting the AGN SED

Nenkova et al., 2002Granato & Danese, 1994

i i

ii FF

N 2

2mod,obs,2 )(1

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 detectionsFi = fluxes


Fitting results (1): MIR continuum & Si (10 μm) feature

Nenkova et al.

Margherita Bonzini

Granato & Danese


Fitting results (2)

Margherita Bonzini

Granato & Danese

Nenkova et al.

Margherita BonziniIMPRS workshop, Garching, Feb 9-11, 2010

Granato & Danese best-fit parameters

About 2/3 of the objects require highly inclined tori with high optical depth

agn9, ferrara, 24-27 maggio 2010 new insights on the torus models from high-resolution seds of...

Documents

outline margherita bonzini

summary margherita bonzini

milano slide

host galaxy interplay

similar slide

obscured agn fraction

dust thermal emission

host galaxy optical