The Evolution of AGN Obscuration

The Evolution of The Evolution of AGN ObscurationAGN Obscuration

Ezequiel Treister (ESO)Ezequiel Treister (ESO)Meg Urry (Yale)

Julian Krolik (JHU)Shanil Virani (Yale)

Priya Natarajan (Yale)

Active Galactic Nucleus Active Galactic Nucleus (AGN)(AGN)

supermassive black hole

actively accreting matter

1-1000 x galaxy luminosity from few lt-hrs

Host Galaxy

The AGN Unified ModelThe AGN Unified Model

blazars, Type 1 Sy/QSO

broad lines

Urry & Padovani, 1995


radio galaxies, radio galaxies, Type 2 Sy/QSOType 2 Sy/QSO

narrow linesnarrow lines


Supermassive Black Supermassive Black Holes Holes

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

Many obscured by gas and dustMany obscured by gas and dust

How do we know that?How do we know that?

Local AGN Unification

Explain Extragalactic X-ray “Background”

Observed X-ray Observed X-ray “Background”“Background”

Frontera et al. (2006)

AGN in X-raysAGN in X-rays

Increasing NH

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

X-ray BackgroundX-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.

What do we know so What do we know so far?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:Problems:• Low number of sources• Selection effects: - X-ray selection (missed obscured sources) - Optical incompleteness (no redshifts) - X-ray classification: “K correction”

Meta-SurveyMeta-Survey

• 7 Surveys, • 2341 AGN, 1229 w Ids• 631 Obscured (no broad lines)• 1042<Lx<1046, 0<z<5


Total effective area of meta-Total effective area of meta-surveysurvey


Ratio vs RedshiftRatio 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 LuminosityRatio vs Luminosity






Hasinger et al.



obsc

obsc

bol

IR

f

f

L

L

1

A Changing Torus?A Changing Torus?A change in the IR/NUV flux ratio may indicate a change in torus geometry.

~2x

Granato & DaneseTorus model

Torus StructureTorus StructureSampleSample

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

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

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

Torus StructureTorus StructureBolometric luminosityconstructed from NUVto mid-IR.

No change in NUV/Bolratio with luminosity!

Treister et al, ApJ submitted.

Torus StructureTorus Structure

Change in 24 µm/Bolratio with luminosity!

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


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

Higher values from fIR/fbol method. Obscured AGNObscured AGNmissed by X-raymissed by X-raysurveys. Detectedsurveys. Detectedin mid-IR?in mid-IR?


HST ACS color image (0.3% of GOODS)

HST+Spitzer color image (0.3% of GOODS)

IR Fraction vs FluxIR Fraction vs Flux

Treister et al 2006

AGN are bright IR sources!

IR Luminosity IR Luminosity DistributionDistribution

Treister et al 2006

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

For fainter AGN, the host galaxy makes a significant contribution

Infrared BackgroundInfrared Background

Treister et al 2006

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

Compton Thick AGNCompton 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 SurveyINTEGRAL 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)INTEGRAL Mosaic (2.2 Ms)

Significance Image, 20-50 keVSignificance Image, 20-50 keV

MCG-02-08-014MCG-02-08-014

MCG-02-08-014MCG-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 candidateGood CT AGN candidate

INTEGRAL AGN logN-logSINTEGRAL AGN logN-logS

Treister et al, submitted

Data points from Beckmann et al. 2006

Space Density of CT AGNSpace Density of CT AGN


X-ray background does not constrain density of CT AGN

CT AGN and the XRBCT AGN and the XRB


XRB Intensity

HEAO-1 +40%




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


Gilli et al. 2007



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


CT AGN Space Density

Most likely solution

Gilli et al. 2007

Treister & Urry 2005

X-ray Background X-ray Background SynthesisSynthesis

X-ray Background X-ray Background SynthesisSynthesis

Treister & Urry 2005

SummarySummaryAGN unification can account well for the observed

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

to extragalactic infrared backgroundSurvey at high energies starts to constrain the spatial

density of CT AGN.

The Evolution of AGN Obscuration

Documents

fainter agn

ratio vs redshifttreister

agn host galaxy

xray backgroundtreister

ratio vs redshiftsee

combination of obscured

obscured agnmissed

lower ratio