the evolution of agn obscuration ezequiel treister (eso) meg urry (yale) julian krolik (jhu) shanil...
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The Evolution of AGN Obscuration
Ezequiel Treister (ESO)Meg Urry (Yale)
Julian Krolik (JHU)Shanil Virani (Yale)
Eric Gawiser (Rutgers)
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”
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
NH vs. Luminosity
In general goodagreement betweenoptical and X-rayclassification.
Treister et al in prep.
NH vs. Redshift
Obscuration increases with redshift?
Or selection effect due to X-rays K correction?
Treister et al in prep.
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
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
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 Structure
Change 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)
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 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
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.
redshifts of Chandra deep X-ray sources
GOODS-N
Barger et al. 2002,3, Hasinger et al. 2002, Szokoly et al. 2004
R<24
GOODS-NModelR<24
Dust emission models from Nenkova et al. 2002, Elitzur et al. 2003
Simplest 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