Everything you wanted to know

about the X-ray background …

Everything you wanted to know

about the X-ray background …

Andrea Comastri (INAF-OABologna-Andrea Comastri (INAF-OABologna-Italy)Italy)

Gilli R., Comastri A., Hasinger G. 2006 AA in Gilli R., Comastri A., Hasinger G. 2006 AA in press press

astro-ph/0610939 astro-ph/0610939

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OUTLINE OUTLINE

Demography and evolution of obscured AGN from XRB models -> uncovering the most elusive accreting Black Holes

Does the unified scheme depend from luminosity and redshift ? MISST

Perspectives for future X-ray multi-wavelength surveys and models

ANEW

Demography and evolution of obscured AGN from XRB models -> uncovering the most elusive accreting Black Holes

Does the unified scheme depend from luminosity and redshift ? MISST

Perspectives for future X-ray multi-wavelength surveys and models

ANEW

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Deep X-ray surveys have resolved some 80% of the XRB (below a few keV ) but “only” 50% > 6 keV (Worsley+05) and a few % above 10 keV.

Wealth of X-ray and multi-wavelength follow-up available unlikely to be substantially modified in the next decade or so

Worth to make an effort to constrain the missing population (Compton Thick AGN) and make solid prediction for future missions and for currently ongoing multi- efforts to efficiently select `obscured’ AGN (Risaliti+99, Fiore +03,Tozzi+06,Martinez-Sansigre+05, Georgantopoulos+06; …)

Deep X-ray surveys have resolved some 80% of the XRB (below a few keV ) but “only” 50% > 6 keV (Worsley+05) and a few % above 10 keV.

Wealth of X-ray and multi-wavelength follow-up available unlikely to be substantially modified in the next decade or so

Worth to make an effort to constrain the missing population (Compton Thick AGN) and make solid prediction for future missions and for currently ongoing multi- efforts to efficiently select `obscured’ AGN (Risaliti+99, Fiore +03,Tozzi+06,Martinez-Sansigre+05, Georgantopoulos+06; …)

Why is still worth fitting the XRB ?

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Assuming the same evolution of “known” AGN and the intensity of the 30 keV XRB peak it is possible to estimate the “size” of the “mildly” (24 < logNH < 25) Compton Thick AGN population

A complete (fair) census of the missing Compton Thick AGN is important for BH mass function, SMBH/galaxy evolution, accretion efficicency, Eddington ratios, …

The BH mass density argument could also be used to constrain the number of heavily (logNH > 25; i.e. NGC 1068 like) Compton thick AGN

Assuming the same evolution of “known” AGN and the intensity of the 30 keV XRB peak it is possible to estimate the “size” of the “mildly” (24 < logNH < 25) Compton Thick AGN population

A complete (fair) census of the missing Compton Thick AGN is important for BH mass function, SMBH/galaxy evolution, accretion efficicency, Eddington ratios, …

The BH mass density argument could also be used to constrain the number of heavily (logNH > 25; i.e. NGC 1068 like) Compton thick AGN

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Frontera+06 submittedFrontera+06 submitted

Model schemeModel scheme

• XRB flux uncertain, so use the more robust constraints below 10 keV (eg. source counts) to lock the properties (eg obs/unobs ratio, NH dist.) of the Compton Thin (log NH < 24) AGN

• Estimate the Compton Thin/Unobs. ratio by comparing hard vs. soft XLF.

• Absorption distribution from X-ray counts.

• Include continuum slope dispersion.

• Add Compton thick AGN to fit the 30 keV bump

• Verify assumptions/make predictions on Compton Thick AGN

• XRB flux uncertain, so use the more robust constraints below 10 keV (eg. source counts) to lock the properties (eg obs/unobs ratio, NH dist.) of the Compton Thin (log NH < 24) AGN

• Estimate the Compton Thin/Unobs. ratio by comparing hard vs. soft XLF.

• Absorption distribution from X-ray counts.

• Include continuum slope dispersion.

• Add Compton thick AGN to fit the 30 keV bump

• Verify assumptions/make predictions on Compton Thick AGN

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Unabsorbed:logNH<21

Compton-Thin:21<logNH<24(Compton reflection high energy cut-off 200 keV)

Compton-Thick:

Mildly (log NH =24-25)(NGC 6240, Circinus)

Heavily (log NH >25)(NGC1068)

Dispersion Dispersion = 0.2 = 0.2

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Hard XLF=Compton Thin + unobscured

Ueda+03La Franca+05

Soft XLF=unobscured

(Hasinger+05)La Franca+05La Franca+05

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Best fit Best fit ratiosratios

~ 4 at low ~ 4 at low Log Lx < 44Log Lx < 44LuminositiesLuminosities

~ 1 at high~ 1 at highLog Lx > 44Log Lx > 44luminositiesluminosities

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Obscured AGN fraction vs luminosity

Observed Intrinsic(i.e. folded with selection effects) Akylas+06

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X-ray logN-logS

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Soft counts areSoft counts aremeasured withmeasured with good accuracygood accuracy

over a large over a large range of fluxesrange of fluxes

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NH distribution

Thick

T h i n

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The fraction of heavily CT depends The fraction of heavily CT depends from the assumed dispersion and from the assumed dispersion and

reflection efficiency (2%) !reflection efficiency (2%) !

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Obscured AGN fraction vs sample limiting flux

ThickThick

All abs.

All abs.

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Correction for Compton-Thick sources from XRB models wholeAGN pop considered

The only free parameters are the accretion efficiency and Eddington ratio

L = ε dM/dt c2

L = λ LEdd

Correction for Compton-Thick sources from XRB models wholeAGN pop considered

The only free parameters are the accretion efficiency and Eddington ratio

L = ε dM/dt c2

L = λ LEdd

Marconi+04Marconi+04

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Determine locus in ε-λ plane where there is the best match between local and relic BHMF!

ε=0.04-0.10 λ=0.08-0.5 which are consistent with common ‘beliefs’ on AGNs

Determine locus in ε-λ plane where there is the best match between local and relic BHMF!

ε=0.04-0.10 λ=0.08-0.5 which are consistent with common ‘beliefs’ on AGNs

2%

0.5%10%

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Summary of XRB model results

Summary of XRB model results CT as many as thin , fraction depends from

scattering efficiency, dispersion in spectral slopes and 30 keV intensity

More obscured AGN at low L -> at QSO luminosities 1 Thin + 1 Thick for each bright unobscured quasar

A “high” 2-10 keV XRB intensity cannot be easily accounted for without violating other constraints (counts, average spectra,…)

Predictions for the space density of obscured (CT) AGN to be compared with present (Spitzer) and future (Herschel) IR surveys and especially > 10 keV survey (Simbol-X)

CT as many as thin , fraction depends from scattering efficiency, dispersion in spectral slopes and 30 keV intensity

More obscured AGN at low L -> at QSO luminosities 1 Thin + 1 Thick for each bright unobscured quasar

A “high” 2-10 keV XRB intensity cannot be easily accounted for without violating other constraints (counts, average spectra,…)

Predictions for the space density of obscured (CT) AGN to be compared with present (Spitzer) and future (Herschel) IR surveys and especially > 10 keV survey (Simbol-X)

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Luminosity and redshift dependence

Luminosity and redshift dependence

Obscuration (anti)-correlates with Luminosity (Lawrence & Elvis 1982) -> Ueda+03, Hasinger04, La Franca+05 … but see Dwelly & Page 06

The obscured fraction increases with z (La Franca+05, Ballantyne+05, Treister & Urry 06) or remains constant (Ueda+03, Hasinger04, Tozzi+06; Dwelly & Page 06; Akylas+06)

Obscuration (anti)-correlates with Luminosity (Lawrence & Elvis 1982) -> Ueda+03, Hasinger04, La Franca+05 … but see Dwelly & Page 06

The obscured fraction increases with z (La Franca+05, Ballantyne+05, Treister & Urry 06) or remains constant (Ueda+03, Hasinger04, Tozzi+06; Dwelly & Page 06; Akylas+06)

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Need to uniformely sample the Luminosity-Redshift Plane

Take into account selection biases associated to low counting statistic

Incompleteness of spectroscopic redshifts and photo-z uncertainties

Need to uniformely sample the Luminosity-Redshift Plane

Take into account selection biases associated to low counting statistic

Incompleteness of spectroscopic redshifts and photo-z uncertainties

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The Cosmic Cycle of Galaxy and AGN

evolution The Cosmic Cycle of Galaxy and AGN

evolution (Hopkins et al. 2005) Mergers between gas

rich galaxies drive gas which fuel both SF andQSO activity (QSO mode)Obscured growth (ULIRG, SCUBA phase, 4pi Covering ?)

BH feedback expels Gas --> BL QSO

Shut down of BH activity dead quasars (or slowly accreting BH) in red galaxies (radio mode)

The QSO light curvesare mass and obscuration dependent

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AGN activityAGN activity

Models predict bolometric luminosity/properties

bolometric approach is needed for a proper census of SMBH (most of them are obscured or elusive)

Bolometric LF and evolution is a key parameter

(poorly known–”attempt” by Hopkins+06, HX,SX, B-band and 15 micron, obscuration and SEDs are luminosity dependent and likely redshift dependent)

Models predict bolometric luminosity/properties

bolometric approach is needed for a proper census of SMBH (most of them are obscured or elusive)

Bolometric LF and evolution is a key parameter

(poorly known–”attempt” by Hopkins+06, HX,SX, B-band and 15 micron, obscuration and SEDs are luminosity dependent and likely redshift dependent)

The evolution of both brightThe evolution of both brightand faint end can be better and faint end can be better measured with a bolometric measured with a bolometric

approach (modulo Compton Thick)approach (modulo Compton Thick)

SummarySummary A proper census of SMBH demography and

evolution (especially for the most obscured sources) cannot rely only on multi- follow-ups

of X-ray surveys but requires a bolometric approach : multiwavelength selection and in

particular IR (Spitzer) + XRB and Mass density/function arguments -> “IR background as a bonus” Fit the data (XRB, counts, …) with a time

dependent model for the AGN activity to account for Redshift and Luminosity

dependence.

A proper census of SMBH demography and evolution (especially for the most obscured sources) cannot rely only on multi- follow-ups

of X-ray surveys but requires a bolometric approach : multiwavelength selection and in

particular IR (Spitzer) + XRB and Mass density/function arguments -> “IR background as a bonus” Fit the data (XRB, counts, …) with a time

dependent model for the AGN activity to account for Redshift and Luminosity

dependence.