The Evolution of AGN Obscuration

The Evolution of AGN Obscuration

Ezequiel Treister (ESO)Meg Urry (Yale)

Julian Krolik (JHU)Shanil Virani (Yale)

Eric Gawiser (Rutgers)

The AGN Unified Model

blazars, Type 1 Sy/QSObroad lines

Urry & Padovani, 1995

The AGN Unified Modelradio galaxies, Type 2 Sy/QSOnarrow lines


Supermassive Black Holes

Credit: ESO/NASA, the AVO project and Paolo Padovani

Many obscured by gas and dust

How do we know that? Local AGN Unification

Explain Extragalactic X-ray “Background”

Observed X-ray “Background”

Frontera et al. (2006)

AGN in X-rays

Increasing NH

Photoelectric absorptionaffect mostly low energy emission making the observed spectrum look harder.

X-ray Background

Treister & Urry, 2005

XRB well explained using a combination of obscured and unobscured AGN.

• Setti & Woltjer 1989• Madau et al. 1994• Comastri et al. 1995• Gilli et al. 1999,2001• And others…

# w NH > 1023 cm-

2

still uncertain.

Multiwavelength Surveys• Hard X-rays penetrate most obscuration

• Energy re-radiated in infrared• High resolution optical separates host galaxy,

constrains redshifts

E-CDF-S• Chandra Coverage• 0.25 deg2

• FX=~10-16erg cm-2s-1

• ~800 X-ray sources

COSMOS• XMM+Chandra Coverage• 2 deg2

• FX=~10-15erg cm-2s-1

• ~1100 X-ray sources

Extended Chandra Deep Field South

(optical)

Extended Chandra Deep Field South

(x-rays)

Hardness Ratio vs. Luminosity

More unobscuredAGN at high X-ray luminosity?

Treister et al in prep.

NH vs. LuminosityIn general goodagreement betweenoptical and X-rayclassification.


NH vs. RedshiftObscuration increases with redshift?

Or selection effect due to X-rays K correction?


HST ACS color image (0.3% of GOODS)

HST+Spitzer color image (0.3% of GOODS)

IR Fraction vs Flux

Treister et al 2006

AGN are bright IR sources!

IR Luminosity Distribution

Treister et al 2006

On average, AGN are ~10x brighter than normal galaxies

For fainter AGN, the host galaxy makes a significant contribution

X-Ray to mid-IR Ratio Significant separation between obscured and unobscured sources.

Smaller separation at shorter wavelength (host galaxy) and largest at longer wavelength (self-absorption).


Unobscured QSO Template

Obscured QSO Template

X-Ray to mid-IR Ratio More separation at lower luminosities.

Change in the opening angle with luminosity? Larger opening angle, ie less self-absorption.


Infrared Background

Treister et al 2006

AGN (+ host galaxy) contribute ~3-10% of the total extragalactic background light

NH Distribution:What do we know so

far?• More obscured AGN at low luminosity (Steffen et

al. 2003, Ueda et al. 2003, Barger et al. 2005, Akylas et al. 2006)

• More obscured AGN at high-z? (Ueda et al. 2003: No, La Franca et al. 2005: yes, Ballantyne et al. 2006: yes)Problems:• Low number of sources• Selection effects: - X-ray selection (missed obscured sources) - Optical incompleteness (no redshifts) - X-ray classification: “K correction”

Meta-Survey

• 7 Surveys, • 2341 AGN, 1229 w

Ids• 631 Obscured (no broad lines)• 1042<Lx<1046,

0<z<5


Total effective area of meta-survey


Ratio vs Redshift


Ratio vs Redshift


Ratio vs Redshift


Ratio vs Redshift

See also:La Franca et al. 2005Ballantyne et al. 2006Akylas et al. 2006

Key input: Luminosity dependence of obscured AGN fraction.


Ratio vs Luminosity


Ratio vs Luminosity


Ratio vs Luminosity


Hasinger et al.

The AGN Unified Model


obsc

obsc

bol

IR

ff

LL

1

Torus StructureSample

Completely unobscured AGNNarrow redshift range, 0.8<z<1.2Wide range in luminosityData at 24 µm from Spitzer

High L• SDSS DR5 Quasar sample• 11938 quasars, 0.8<z<1.2• 192 with Spitzer 24 µm photometry• 157 of them with GALEX UV data

Low L• GOODS: North+South fields• 10 unobscured AGN• All Spitzer 24 µm photometry• 8 with GALEX UV data

Mid L• COSMOS• 19 unobscured AGN• 14 Spitzer 24 µm photometry• All with GALEX UV data

Torus StructureBolometric luminosityconstructed from NUVto mid-IR.

No change in NUV/Bolratio with luminosity!

Treister et al. 2008

Torus StructureChange in 24 µm/Bolratio with luminosity!

Lower ratio at high L Consistent with larger opening anglesat higher luminosities.


Fraction of Obscured AGNSimilar luminositydependence as foundon X-ray surveys.

Higher values from fIR/fbol method. Obscured AGNmissed by X-raysurveys.


Compton Thick AGN Defined as obscured sources with NH>1024 cm-2. Very hard to find (even in X-rays). Observed locally and needed to explain the X-ray background. Number density highly uncertain. High energy (E>10 keV) observations are required to find them.

INTEGRAL Survey• PIs: Meg Urry, Shanil Virani, Ezequiel Treister• Exp. Time (Msec): 0.7 (archive)+1.5 (2005)+ 1

(2008). Deepest extragalactic INTEGRAL survey• Field: XMM-LSS (largest XMM field)• Flux limit: ~4x10-12 ergs cm-2 s-1 (20-40 keV)• Area: ~1,000 deg2

• Sources: ~20• Obscured AGN: ~15 (~5 Compton-thick)

INTEGRAL Mosaic (2.2 Ms)

Significance Image, 20-50 keV

MCG-02-08-014

MCG-02-08-014• z=0.0168• Optical class: Galaxy• IR source (IRAS)• Radio source (NVSS)• Narrow line AGN (based on OIII emission)• No soft X-rays (ROSAT)• Good CT AGN candidate

Space Density of CT AGN

Treister et al, submitted

X-ray background does not constrain density of CT AGN

CT AGN and the XRB


XRB Intensity

HEAO-1 +40%


CT AGN and the XRB


XRB IntensityHEAO-1 OriginalHEAO-1 +10%HEAO-1 +40%


Gilli et al. 2007

CT AGN and the XRB


XRB IntensityHEAO-1 OriginalHEAO-1 +10%HEAO-1 +40%


CT AGN Space Density

Most likely solution

Gilli et al. 2007

X-ray Background Synthesis

NH Distribution

SummaryAGN unification can account well for the observed

properties of the X-ray background.AGN are luminous infrared sources, but contribute ~5%

to extragalactic infrared backgroundThe obscured AGN fraction decreases with increasing

luminosity. Ratio of IR to Bolometric luminosity in unobscured AGN

suggest this is due to a change in opening angle.The obscured AGN fraction increases with redshift as

(1+z)0.4.Survey at high energies starts to constrain the spatial

density of CT AGN.

SBH Spatial Density

Natarajan & Treister, in prep

XRB Intensity

Ratio vs Luminosity


Luminosity vs Redshift


Incompleteness Effects


redshifts of Chandra deep X-ray sourcesGOODS-N

Barger et al. 2002,3, Hasinger et al. 2002, Szokoly et al. 2004

R<24GOODS-NModelR<24

Dust emission models from Nenkova et al. 2002, Elitzur et al. 2003Simplest dust distribution that satisfies

NH = 1020 – 1025 cm-2

3:1 ratio (divide at 1022 cm-2)Random angles NH distribution

NH=1025cm-2

NH=1022cm-2

NH=1020cm-2

Space Density of CT AGN


Strong degeneracy between reflection component and number of CT AGN.

The Evolution of AGN Obscuration

Documents

xray spectrum

xray background spectrum

high xray luminosity

agn unification paradigm

local agn unification

xray backgroundtreister

observed spectrum

treister et