X-Ray Emission From The Nuclei X-Ray Emission From The Nuclei of Radio Galaxiesof Radio Galaxies

Daniel EvansDaniel EvansUniversity of BristolUniversity of Bristol

-with--with-Diana Worrall, Ralph Kraft, Martin Hardcastle, Mark Diana Worrall, Ralph Kraft, Martin Hardcastle, Mark

Birkinshaw, Judith Croston, Bill Forman, Christine Jones, Birkinshaw, Judith Croston, Bill Forman, Christine Jones, Steve MurraySteve Murray

ContentsContents

An introduction to AGN physicsAn introduction to AGN physics X-ray emission from radio galaxies: X-ray emission from radio galaxies:

the issuesthe issues Centaurus A: the nearest AGNCentaurus A: the nearest AGN NGC 6251: a counterexample?NGC 6251: a counterexample? Nuclear emission from a sample of Nuclear emission from a sample of

3CRR radio galaxies3CRR radio galaxies ConclusionsConclusions

What are AGN?What are AGN?

Unresolved nuclear componentUnresolved nuclear component Nuclear luminosity > sum of all starsNuclear luminosity > sum of all stars MMBHBH ~ 10 ~ 1066–10–101010 M M๏๏ Accompanied by strong X-ray emissionAccompanied by strong X-ray emission

NGC 3277 NGC 5548 NGC 6251 - XMM

The Central EngineThe Central Engine

Accretion flow surrounded by dusty torusAccretion flow surrounded by dusty torus

The Central EngineThe Central Engine

Accretion flow surrounded by dusty torusAccretion flow surrounded by dusty torus BB radiation from disk BB radiation from disk ‘big blue bump’ ‘big blue bump’

The Central EngineThe Central Engine

Accretion flow surrounded by dusty torusAccretion flow surrounded by dusty torus BB radiation from disk BB radiation from disk ‘big blue bump’ ‘big blue bump’ B-field loops B-field loops optically thin corona optically thin corona

The Central EngineThe Central Engine

Accretion flow surrounded by dusty torusAccretion flow surrounded by dusty torus BB radiation from disk BB radiation from disk ‘big blue bump’ ‘big blue bump’ B-field loops B-field loops optically thin corona optically thin corona IsotropicIsotropic X-rays from Comptonization of disk photons in hot corona X-rays from Comptonization of disk photons in hot corona Power law spectrumPower law spectrum

Fe KFe K Production Production Reflection of X-rays from an optically thick accretion diskReflection of X-rays from an optically thick accretion disk

Fe KFe K Production Production Reflection of X-rays from an optically thick accretion diskReflection of X-rays from an optically thick accretion disk

Fe KFe K Production Production Reflection of X-rays from an optically thick accretion diskReflection of X-rays from an optically thick accretion disk

Fe KFe K Production Production Reflection of X-rays from an optically thick accretion diskReflection of X-rays from an optically thick accretion disk

Fe KFe K Production Production Reflection of X-rays from an optically thick accretion diskReflection of X-rays from an optically thick accretion disk

Fe KFe K Production Production Reflection of X-rays from an optically thick accretion diskReflection of X-rays from an optically thick accretion disk

Fe Kα

Astrophysical JetsAstrophysical Jets

10 pc

NGC 62515 GHz VLBIJones et al. (1986)

AnisotropicAnisotropic emission, power law spectrum emission, power law spectrum Relativistic Doppler beaming, dependent on bulk speed (Relativistic Doppler beaming, dependent on bulk speed (ΓΓ), angle to ), angle to

line of sightline of sight

Radio Galaxy Nuclei – Two Competing Radio Galaxy Nuclei – Two Competing ModelsModels

Is the X-ray Is the X-ray emission emission dominated by:dominated by:

The parsec-scale The parsec-scale jet?jet?

-or--or- The accretion flow?The accretion flow?

Jet-Related EmissionJet-Related Emission

e.g., Zamorani et al. (1981)

1.1. For a given optical For a given optical luminosity, radio-loud luminosity, radio-loud quasars are brighter X-quasars are brighter X-ray sources than radio-ray sources than radio-quiet quasarsquiet quasars

An additional An additional component of emission component of emission is present in RLQsis present in RLQs

Three Discoveries:Three Discoveries:

Jet-Related EmissionJet-Related Emission

2.2. Dependence of X-ray Dependence of X-ray luminosity and spectrum luminosity and spectrum on beaming angleon beaming angle

A component is A component is anisotropicanisotropic

3.3. Correlation between Correlation between ROSATROSAT soft X-ray and soft X-ray and radio fluxes and radio fluxes and luminositiesluminosities

Soft X-ray emission Soft X-ray emission likely jet-relatedlikely jet-related

Shastri et al. (1993)

Canosa et al. (1999)

Accretion-Related EmissionAccretion-Related Emission

Have seen that soft (0.5-2.4 keV) X-ray emission likely jet Have seen that soft (0.5-2.4 keV) X-ray emission likely jet relatedrelated

What about the rest of the X-ray spectrum? Jet or What about the rest of the X-ray spectrum? Jet or accretion flow?accretion flow?

E.g. Gliozzi et al. (2004) claim broadened Fe KE.g. Gliozzi et al. (2004) claim broadened Fe K emission emission and variability on short timescales in NGC 6251and variability on short timescales in NGC 6251

Would imply accretion-dominated emissionWould imply accretion-dominated emission

d < ct

Summary of IntroductionSummary of Introduction

Emission in the nuclei Emission in the nuclei of AGN consists of:of AGN consists of:– ““Radio-quiet” Radio-quiet”

accretion-related accretion-related componentcomponent

– ““Radio-loud” jet-Radio-loud” jet-related componentrelated component

Which dominates the Which dominates the X-ray emission?X-ray emission?– Matter of Matter of

considerable considerable debate…debate…

Cen A – The Nearest AGNCen A – The Nearest AGN

Brightest Brightest extragalactic object extragalactic object in the hard X-ray skyin the hard X-ray sky

Closest radio galaxy Closest radio galaxy (d = 3.4 Mpc)(d = 3.4 Mpc)

Complex emissionComplex emission Ideal object to studyIdeal object to study Much-studied by Much-studied by

earlier X-ray earlier X-ray missionsmissions

Rich gallery of radio Rich gallery of radio features (jet, lobes, features (jet, lobes, etc.)etc.)

Chandra 0.5-2 keV X-ray

Continuum SpectrumContinuum Spectrum

Attempt to fit a heavily-absorbed (Attempt to fit a heavily-absorbed (NNHH 10 102323 atoms cmatoms cm-2-2) power-law () power-law (ΓΓ 1.7) 1.7)

Significant residuals below Significant residuals below 2.5 keV 2.5 keV

XMM-Newton MOS2 1st observation

Continuum SpectrumContinuum Spectrum

Significant improvement with the addition of a Significant improvement with the addition of a secondsecond power- power-law componentlaw component

ComponeComponentnt

NNHH (atoms cm (atoms cm-2-2)) ΓΓ

Hard PLHard PL (1.30 (1.30 ±± 0.16) x 0.16) x 10102323

1.76 1.76 ±± 0.150.15

Soft PLSoft PL (3.8 (3.8 ±± 2.0) x 10 2.0) x 102222 2 (frozen)2 (frozen)

Key parameters:

Possible Origin of 2Possible Origin of 2ndnd PL PL

VLBI jet? Flux density VLBI jet? Flux density 5 Jy at 4.8 GHz 5 Jy at 4.8 GHz X-ray to radio ratio for 2X-ray to radio ratio for 2ndnd PL and VLBI jet consistent with that of PL and VLBI jet consistent with that of

kpc-scale jet and VLA jetkpc-scale jet and VLA jet Mildly absorbed soft power law seen in other FRI galaxies with Mildly absorbed soft power law seen in other FRI galaxies with

ROSATROSAT

Canosa et al. (1999)Canosa et al. (1999)

0.7 pc

Core

Tingay et al. (1998)Tingay et al. (1998)

Fluorescent Line EmissionFluorescent Line Emission

ChandraChandra HETGS instrument of choice due to its high spectral resolution HETGS instrument of choice due to its high spectral resolution

Fe K

Fe K

Joint HEG+1 and HEG-1 spectrum

Fe KFe K centroid = centroid = 6.4046.404±±0.002 keV (90% 0.002 keV (90% c.l.)) c.l.)) fluorescence fluorescence from cold, neutral from cold, neutral materialmaterial

Fe KFe Kαα is broadened is broadened ((σσ = 20 = 20±±10 eV (90% 10 eV (90% c.l.)) c.l.)) v v ~~ 1000 km s 1000 km s-1-1

r r ~~ 0.1 pc 0.1 pc

(M(MBHBH = 2 x 10 = 2 x 1088 M M๏๏))

Geometry Of Emission RegionGeometry Of Emission Region

Fe KFe K line parameters consistent with fluorescence line parameters consistent with fluorescence from from NNHH 10 102323 atoms cm atoms cm-2 -2 with torus geometrywith torus geometry

Also consistent with fluorescence from Also consistent with fluorescence from NNHH ~~ 10 102424 atoms cmatoms cm-2-2 outside line of sight (Woźniak et al. outside line of sight (Woźniak et al. 1998)1998)

Nature of Accretion FlowNature of Accretion Flow

GalaxyGalaxy LLxx LLEddEdd BondiBondi InterpretationInterpretation

Cen ACen A 4.8 4.8 x x 10104141

2.6 2.6 x x 10104646

2.3 2.3 x 10x 10-3-3 Hybrid?Hybrid?

Sag A*Sag A* 2.4 2.4 x x 10103333

3.3 3.3 x x 10104444

2.4 2.4 x 10x 10-9-9 InefficientInefficient

NGC NGC 44724472

6.4 6.4 x x 10103838

7.2 7.2 x x 10104646

1.4 1.4 x 10x 10-6-6 InefficientInefficient

3C 390.33C 390.3 5.0 5.0 x x 10104444

4.4 4.4 x x 10104646

1.1 1.1 x 10x 10-2-2 StandardStandard

Hybrid inefficient flow/thin disk

Cen A SummaryCen A Summary

Emission characterized by a heavily-Emission characterized by a heavily-absorbed power lawabsorbed power law

Second power-law component Second power-law component necessary, consistent with VLBInecessary, consistent with VLBI jetjet

Fluorescent lines from cold, neutral Fluorescent lines from cold, neutral materialmaterial

Molecular torus?Molecular torus? Accretion flow: Hybrid?Accretion flow: Hybrid? More info: Evans et al. (2004), ApJ, 612, More info: Evans et al. (2004), ApJ, 612,

786786

NGC 6251 – A NGC 6251 – A CounterexampleCounterexample

z=0.0244 (dz=0.0244 (d~100 Mpc) ~100 Mpc) FRI-type FRI-type radio galaxyradio galaxy

Spectacular radio jet extending Spectacular radio jet extending hundreds of kpchundreds of kpc

Opening angle of 7.4Opening angle of 7.4oo

X-ray emission from nucleus X-ray emission from nucleus and three regions of kpc-scale and three regions of kpc-scale jetjet

Synchrotron interpretation for Synchrotron interpretation for kpc-scale jet (Evans et al. 2005)kpc-scale jet (Evans et al. 2005)

1 arcmin

30 kpc

1.6 GHz VLAJones et al. (1986)

0.5-5 keV Chandra image with 1.6 GHz VLA contours (Evans et al. 2005)

NGC 6251 - ResultsNGC 6251 - Results

XMM-Newton observation XMM-Newton observation of NGC 6251. Gliozzi et of NGC 6251. Gliozzi et al. (2004) claimed al. (2004) claimed broadened Fe Kbroadened Fe K line- line-emissionemission

Would imply accretion-Would imply accretion-dominated X-ray dominated X-ray emissionemission

New New ChandraChandra data + data + reanalysis of XMM datareanalysis of XMM data

Nuclear spectrum well Nuclear spectrum well fitted with a featureless, fitted with a featureless, single, unabsorbed single, unabsorbed power lawpower law

1 2 4 7Energy (keV)

Chandra

XM

M

NGC 6251 – Fe KNGC 6251 – Fe K line line No evidence of Fe KNo evidence of Fe K emission in emission in ChandraChandra spectrum spectrum No significant evidence for Fe KNo significant evidence for Fe K emission in XMM spectrum emission in XMM spectrum

Already evidence to disfavour accretion-dominated X-ray emissionAlready evidence to disfavour accretion-dominated X-ray emission

NGC 6251 - InterpretationNGC 6251 - Interpretation

1-keV X-ray flux density consistent with ROSAT soft X-ray results1-keV X-ray flux density consistent with ROSAT soft X-ray results Also consistent with soft power law observed in Cen AAlso consistent with soft power law observed in Cen A SED double-peaked and modelled by SSC emissionSED double-peaked and modelled by SSC emission X-ray emission dominated by a jetX-ray emission dominated by a jet

Intermediate SummaryIntermediate Summary

Dissimilar spectra for two Dissimilar spectra for two seemingly similar FRI-type radio seemingly similar FRI-type radio galaxies:galaxies:– Cen A: X-ray emission hard and Cen A: X-ray emission hard and

heavily absorbed (likely accretion-heavily absorbed (likely accretion-related), accompanied by soft related), accompanied by soft emissionemission

– NGC 6251: X-ray emission soft and NGC 6251: X-ray emission soft and unabsorbedunabsorbed

Soft emission of Cen A may have Soft emission of Cen A may have the same origin as that of NGC the same origin as that of NGC 62516251

Why might they be dissimilar?Why might they be dissimilar? Are both accretion-related and jet-Are both accretion-related and jet-

related components present in related components present in allall radio galaxies at varying levels?radio galaxies at varying levels?

Need to study a sampleNeed to study a sample

1 2 4 7Energy (keV)

Cen A

NG

C 6

251

The 3CRR SampleThe 3CRR Sample

Criteria:Criteria:– 178-MHz luminosity density > 178-MHz luminosity density >

10.9 Jy10.9 Jy– Declination > 10Declination > 10oo

– ||bb| > 10| > 10oo

Advantages:Advantages:– No orientation biasNo orientation bias– Spectroscopic identificationSpectroscopic identification– High-resolution radio High-resolution radio

observationsobservations Select sources with Select sources with zz<0.1<0.1

– Unambiguously spatially Unambiguously spatially separate unresolved nuclear separate unresolved nuclear emission from contaminating emission from contaminating emissionemission

– Rich variety (FRI/FRII, Rich variety (FRI/FRII, broad/narrow lines, large broad/narrow lines, large luminosity range)luminosity range)

19/38 X-ray observations of low-z 19/38 X-ray observations of low-z 3CRRs, 16 of them with 3CRRs, 16 of them with ChandraChandra

Complete spectral analysis of Complete spectral analysis of eacheach

The 3CRR SampleThe 3CRR Sample

VLA (Leahy, Bridle, & Strom) Chandra 0.5-5 keV

The 3CRR Sample: AimsThe 3CRR Sample: Aims Dominant X-ray emission Dominant X-ray emission

mechanism:mechanism:– Accretion Flow: Accretion Flow:

Fe KFe K, variability, variability

-or--or-– Jet:Jet:

SED, radio-SED, radio-optical-X-ray optical-X-ray luminosity correlationsluminosity correlations

Nature of accretion flow: Nature of accretion flow: thin disk? RIAF?thin disk? RIAF?

IIs the torus ubiquitous?s the torus ubiquitous? FRI-FRII dichotomy?FRI-FRII dichotomy?

Unified AGN scheme:Unified AGN scheme:

Consider Consider LLXX and and LLRR Considerable scatterConsiderable scatter

Luminosity-Luminosity Luminosity-Luminosity CorrelationsCorrelations

5-GHz luminosity density (W Hz-1 sr-1)

1020 1021 1022 1023 1024 1025

1-ke

V lu

min

osity

den

sity

(W

Hz-1

sr-1

)

1013

1014

1015

1016

1017

1018

1019

Consider Consider LLXX and and LLRR Considerable scatterConsiderable scatter Much better Much better

correlation between correlation between components with components with NNHH ≤ 5 x 10≤ 5 x 102222

Most components Most components have have NNHH consistent consistent with 0with 0

Any intrinsic Any intrinsic absorption consistent absorption consistent with dust in host with dust in host galaxygalaxy

Origin of X-ray Origin of X-ray emission in pc-scale emission in pc-scale jet (outside any jet (outside any torus)torus)

Luminosity-Luminosity Luminosity-Luminosity CorrelationsCorrelations

5-GHz luminosity density (W Hz-1 sr-1)

1020 1021 1022 1023 1024 1025

1-ke

V lu

min

osity

den

sity

(W

Hz-1

sr-1

)

1013

1014

1015

1016

1017

1018

1019

NH ≤ 5 x 1022

Jet

Components with Components with NNHH ~ ~ 10102323 lie above trendline lie above trendline

As does 3C 390.3, As does 3C 390.3, unobscured BLRGunobscured BLRG

All have Fe KAll have Fe K lines lines Accretion-dominated Accretion-dominated

and surrounded by a and surrounded by a torus?torus?

Soft components of Soft components of these sources these sources consistent with jet-consistent with jet-related trendline related trendline

Accretion and jet Accretion and jet components present in components present in all radio galaxies at all radio galaxies at varying levels?varying levels?

7/8 are FRIIs, other is 7/8 are FRIIs, other is Cen ACen A

Luminosity-Luminosity Luminosity-Luminosity CorrelationsCorrelations

5-GHz luminosity density (W Hz-1 sr-1)

1020 1021 1022 1023 1024 1025

1-ke

V lu

min

osity

den

sity

(W

Hz-1

sr-1

)

1013

1014

1015

1016

1017

1018

1019

NH ≤ 5 x 1022

5-GHz luminosity density (W Hz-1 sr-1)

1020 1021 1022 1023 1024 1025

1-ke

V lu

min

osity

den

sity

(W

Hz-1

sr-1

)

1013

1014

1015

1016

1017

1018

1019

NH ≤ 5 x 1022

NH ~ 1023

Jet

Accretion

So far:So far:– X-ray emission of FRIIs is heavily X-ray emission of FRIIs is heavily

absorbed and accompanied by absorbed and accompanied by Fe KFe K lines lines accretion-related accretion-related and viewed through a torusand viewed through a torus

– X-ray emission of FRIs much less X-ray emission of FRIs much less absorbed. absorbed. LLXX and and LLRR

correlations correlations jet-related emission jet-related emission

Where is the torus in FRIs? Where is the torus in FRIs? Problems with unified models, Problems with unified models, etc.etc.

Find upper limits to accretion-Find upper limits to accretion-related emission in FRIsrelated emission in FRIs

Data don’t exclude luminosities Data don’t exclude luminosities of ~ 10of ~ 103939-10-104141 ergs/s ergs/s

Some comparable to, e.g., Cen A Some comparable to, e.g., Cen A (5x10(5x104141 ergs/s) but lower than ergs/s) but lower than FRIIs (10FRIIs (104343-10-104444 ergs/s) ergs/s)

A Nuclear FRI/FRII Dichotomy?A Nuclear FRI/FRII Dichotomy?

e.g. 3C 274 (M87)

Data do not exclude the presence of a torus in FRIs Data do not exclude the presence of a torus in FRIs supports AGN- supports AGN-unification modelsunification models

FRI nuclei are FRI nuclei are notnot simply scaled versions of FRIIs simply scaled versions of FRIIs– For a given jet power, FRI nuclei have less efficient accretion flowsFor a given jet power, FRI nuclei have less efficient accretion flows– Dichotomy in accretion-flow structure of FRIs and FRIIsDichotomy in accretion-flow structure of FRIs and FRIIs

The FRI/FRII dichotomy is not just related to differences in the The FRI/FRII dichotomy is not just related to differences in the medium into which jet propagatesmedium into which jet propagates

First evidence of dichotomy from X-ray studiesFirst evidence of dichotomy from X-ray studies

A Nuclear FRI/FRII Dichotomy?A Nuclear FRI/FRII Dichotomy?

Implications:Implications:

MHD ADAF SimulationArmitage (2004)

SummarySummary

Unobscured (jet-related), and obscured Unobscured (jet-related), and obscured (accretion-related) components present (accretion-related) components present in all radio galaxies at varying levelsin all radio galaxies at varying levels

Data do not exclude the presence of a Data do not exclude the presence of a torus in FRI-type sourcestorus in FRI-type sources

An FRI/FRII dichotomy exists on nuclear An FRI/FRII dichotomy exists on nuclear scalesscales