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

Urry & Padovani, 1995

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.

Treister et al in prep.

NH vs. RedshiftObscuration increases with redshift?

Or selection effect due to X-rays K correction?

Treister et al in prep.

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).

Treister et al in prep.

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.

Treister et al in prep.

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

Treister & Urry, 2006

Total effective area of meta-survey

Treister & Urry, 2006

Ratio vs Redshift

Treister & Urry, 2006

Ratio vs Redshift

Treister & Urry, 2006

Ratio vs Redshift

Treister & Urry, 2006

Ratio vs Redshift

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

Key input: Luminosity dependence of obscured AGN fraction.

Treister & Urry, 2006

Ratio vs Luminosity

Treister & Urry, 2006

Ratio vs Luminosity

Treister & Urry, 2006

Ratio vs Luminosity

Treister & Urry, 2006

Hasinger et al.

The AGN Unified Model

Urry & Padovani, 1995

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.

Treister et al. 2008

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

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

Treister et al. 2008

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

Treister et al, submitted

XRB Intensity

HEAO-1 +40%

Treister & Urry, 2005

CT AGN and the XRB

Treister et al, submitted

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

Treister & Urry, 2005

Gilli et al. 2007

CT AGN and the XRB

Treister et al, submitted

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

Treister & Urry, 2005

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

Treister & Urry, 2006

Luminosity vs Redshift

Treister & Urry, 2006

Incompleteness Effects

Treister & Urry, 2006

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

Treister et al, submitted

Strong degeneracy between reflection component and number of CT AGN.