Transcript
Page 1: SEARCHING FOR COOLING FLOWS… Silvia Caffi IASF/CNR Sez. Milano

SEARCHING FOR SEARCHING FOR COOLING COOLING FLOWS…FLOWS…

Silvia CaffiSilvia Caffi

IASF/CNR Sez. Milano IASF/CNR Sez. Milano

Page 2: SEARCHING FOR COOLING FLOWS… Silvia Caffi IASF/CNR Sez. Milano

X-RAY SPECTRA:X-RAY SPECTRA:emission from optically thin emission from optically thin thermal plasma polluted by thermal plasma polluted by heavy elementsheavy elements

typical values: ntypical values: nee ~ 10 ~ 10-4-4 – 10 – 10-2 -2

cmcm-3-3, T, Tgg ~ 10 ~ 107 7 – 10– 1088 K (heavily K (heavily ionized gas), R ~ 1 Mpc.ionized gas), R ~ 1 Mpc.

No absorption

Exponential cut-

off

IMAGING:IMAGING:central regions feature ~ central regions feature ~ constant surface brightnessconstant surface brightness

in outer regions S.B. falls off in outer regions S.B. falls off as a power-law with index ~ 3as a power-law with index ~ 3

emission is traced out to 1-2 emission is traced out to 1-2 Mpc from the coreMpc from the core

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Properties of the Intra Cluster Properties of the Intra Cluster Medium:Medium:

hot, heavely ionized and tenouos gas at rest hot, heavely ionized and tenouos gas at rest in the potential well of the clusterin the potential well of the cluster

dissipates energy at a very slow rate by X dissipates energy at a very slow rate by X raysrays

2/1

8

1

3310

1010105.8

K

T

cm

nyrxt gp

cool

considered as a fluid in hydrostatic considered as a fluid in hydrostatic equilibriumequilibrium

Hubblecoolsound

gsound

gsound

tttK

T

MpcD

yrxt

Tp

v

2/1

88

2/12/1

10106.6

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ttcool cool ~ T~ Tgg1/2 1/2 nnpp

-1-1

for large radii nfor large radii npp is is smallsmallin the core nin the core npp is large is large

ttcool cool << t<< tHubbleHubble

ttcool cool ~ t~ tHubbleHubble

COOLING FLOW COOLING FLOW CLUSTERSCLUSTERSsurface brightness surface brightness

strongly peaked at the strongly peaked at the centercenterlow ionization lines in low ionization lines in soft X-ray spectrasoft X-ray spectra

temperature temperature gradients toward the gradients toward the center center Canizares Canizares et al. et al. (1984)(1984)De Grandi & MolendiDe Grandi & Molendi (2002)(2002)

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In-homogenous model for CF (Nulsen In-homogenous model for CF (Nulsen 1984)1984)

multiphaseness of the gas: different phases (T multiphaseness of the gas: different phases (T and and ρρ) coexist, in pressure equilibrium (t) coexist, in pressure equilibrium (tsound sound < < ttcoolcool) at every r) at every rthe phases comove, under the pressure of the the phases comove, under the pressure of the gas immediately on top, with <v> << vgas immediately on top, with <v> << vsoundsound..

at T~10at T~1066 K t K tcool cool ~ t~ tsound sound : the cold blob decouples : the cold blob decouples from the flow while the others continue to flow from the flow while the others continue to flow inward. inward. the mass deposition rate scales as rthe mass deposition rate scales as rαα, implyng , implyng that deposition occurs everywhere in the that deposition occurs everywhere in the cooling flow region. Typical value for mass dep. cooling flow region. Typical value for mass dep. rate: dM/dt=100Mrate: dM/dt=100Msunsun/yr/yr

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cooling flows are seen in a large number of cooling flows are seen in a large number of clusters (clusters (~ 60% - 70%~ 60% - 70%), so they can be ), so they can be resonably considered as persistent resonably considered as persistent phenomenaphenomena

suncDacc

sunclusteracc

sunsunacc

MMM

MMM

yrMdrdM

MM

12

1514

12

10

1010

/100/

10

Cold gasCold gas

IONIZEDIONIZED

NEUTRALNEUTRAL

MOLECULARMOLECULAR

lines observed in optical and UV lines observed in optical and UV indicate that ionized gas is present indicate that ionized gas is present but << Mbut << Maccacc21 cm observations in central 21 cm observations in central galaxies give Mgalaxies give MHIHI < 10 < 1099 M Msunsun

recent observations (Edge 2002) recent observations (Edge 2002) have detected molecular gas for have detected molecular gas for the first time, again << Mthe first time, again << Maccacc

Hubbleacc tdtdM

M

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XMM point of viewXMM point of view

EPIC cannot resolve individual EPIC cannot resolve individual lines but can discriminate bet. lines but can discriminate bet. models with and without a models with and without a minimum temperature:minimum temperature:

In RGS spectra there is a In RGS spectra there is a remarkable lack of emission remarkable lack of emission lines expected from gas cooling lines expected from gas cooling below 1-2 keV (see for example below 1-2 keV (see for example the sample of 14 objects in the sample of 14 objects in Petersen 2003 ... )Petersen 2003 ... )

TTminmin=0.9 keV: the shoulder is =0.9 keV: the shoulder is absent because the low ionization absent because the low ionization lines are missing.lines are missing.TTminmin=0.1 keV: we see a shoulder =0.1 keV: we see a shoulder down to ~ 0.8 keV, due to low down to ~ 0.8 keV, due to low ionization lines from gas colder ionization lines from gas colder than 0.9 keV.than 0.9 keV.

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both EPIC and RGS both EPIC and RGS mesurements mesurements indicate Tindicate Tminmin in in [1,3] keV [1,3] keV

standard cooling flow standard cooling flow model predicts gas model predicts gas with T down to at with T down to at least 0.1 keV!least 0.1 keV!

BUTBUT

gas is NOT multiphase, at least not in the gas is NOT multiphase, at least not in the sense required by the standard multi-phase sense required by the standard multi-phase

CF modelCF model

FAILURE OF THE FAILURE OF THE STANDARD CF MODELSTANDARD CF MODEL

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If CFs are not observed something If CFs are not observed something must quench them:must quench them: HEATING HEATING

MECHANISMMECHANISM feedback from AGNfeedback from AGN: : Chandra observation clearly Chandra observation clearly show interaction between AGN show interaction between AGN and the ICM (radio lobes/ X-and the ICM (radio lobes/ X-ray cavities)ray cavities)

Perseus (Fabian Perseus (Fabian et alet al 2002) 2002)

efficient mechanism only in efficient mechanism only in cluster cluster corescores: too high M: too high MBHBH are required to are required to completely quench a luminous CF completely quench a luminous CF (Fabian 2002)(Fabian 2002)

thermal conductionthermal conduction: large : large heat reservoir in the outer heat reservoir in the outer regions of clusters, if regions of clusters, if ΔT/TΔT/T is is large this mechanism large this mechanism should be efficientshould be efficient

estimates of estimates of κκeffeff(r) show that this (r) show that this mechanism is efficient only in mechanism is efficient only in outermost regionsoutermost regions: for innermost : for innermost ones κones κeffeff exceeds κ exceeds κs s (Ghizzardi (Ghizzardi et alet al. . 2003)2003)

MIXED MODELSMIXED MODELS

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First candidate: First candidate: A2199A2199nearby cluster z = 0.030, D = 131.6 Mpc nearby cluster z = 0.030, D = 131.6 Mpc (H(H0 0 = 70 = 70 km/s/Mpckm/s/Mpc))strong X-ray emission peaked on NGC6166: Lstrong X-ray emission peaked on NGC6166: LXX = 6.43 x 10 = 6.43 x 104444 erg/s erg/s

kT kT ~ 4.7 keV (Peres 1998), <Z> = 0.35 (De Grandi & Molendi 2001)~ 4.7 keV (Peres 1998), <Z> = 0.35 (De Grandi & Molendi 2001)

why A2199 is a good subject for our quest?why A2199 is a good subject for our quest?extremely relaxed cluster, no evidence for azimuthal extremely relaxed cluster, no evidence for azimuthal gradients in our kT and metallicity maps (XMM data) gradients in our kT and metallicity maps (XMM data)

lack of evidences for interaction bet. cD galaxy and ICM lack of evidences for interaction bet. cD galaxy and ICM in Chandra images (sharper eyes than XMM-Newton)in Chandra images (sharper eyes than XMM-Newton)

very luminous in X band ( some 10very luminous in X band ( some 104444 erg/s) erg/s)

IT LOOKS LIKE A CLUSTER IT LOOKS LIKE A CLUSTER HARBOURING A STRONG COOLING HARBOURING A STRONG COOLING

FLOWFLOW

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rr cooli

ng

cooli

ng

spectral models applied to spectral models applied to A2199:A2199:single temperature (wabs*mekal in XSPEC): 4 free single temperature (wabs*mekal in XSPEC): 4 free

parameters kT, redshift, abundance and normalization of parameters kT, redshift, abundance and normalization of the thermal component.the thermal component.two temperature (wabs*(mekal+mekal) in XSPEC): two two temperature (wabs*(mekal+mekal) in XSPEC): two additional free parameters are T and normalization of the additional free parameters are T and normalization of the second component. second component.

comparison bet. 1T and 2T comparison bet. 1T and 2T models:models:1T has good residuals, suggesting 1T has good residuals, suggesting no need for other no need for other

components components we placed upper limits to the contribution of an eventual we placed upper limits to the contribution of an eventual cool component: in the innermost region temperatures cool component: in the innermost region temperatures below below 1.0 keV1.0 keV are ruled out, in the second bin (0.5-1.0 are ruled out, in the second bin (0.5-1.0 arcmin) the value of arcmin) the value of TTminmin rises up to rises up to 1.2 keV1.2 keV! !

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Let’s make the point on the first Let’s make the point on the first candidate!candidate!

a promising a promising cluster ...cluster ...

BUTBUTthe ICM is well described by a the ICM is well described by a 1T model1T model. A . A second component, if present, cannot be second component, if present, cannot be cooler than ~ cooler than ~ 1 keV1 keV (from spectral analysis) (from spectral analysis)

luminoluminoususvery relaxedvery relaxedT and ZT and ZFeFe gradientsgradients

SOSO

NO CF IN A2199!!!NO CF IN A2199!!!

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Second candidate: Second candidate: A1068A1068more distant than A2199 z = 0.1386, D = 645 Mpc more distant than A2199 z = 0.1386, D = 645 Mpc (h(h00 = = 0.7)0.7)X-ray emission peaked on cluster centerX-ray emission peaked on cluster center

kT kT ~ 4.0 keV, <Z> ~ 0.5 (Wise et al. 2004)~ 4.0 keV, <Z> ~ 0.5 (Wise et al. 2004)

why A1068 is a good subject for our quest?why A1068 is a good subject for our quest?

elliptical shape (elliptical shape (ε = 0.71ε = 0.71), complicated central morphology (r<50 kpc)), complicated central morphology (r<50 kpc)

mesures of CO emission lines tell us that a mesures of CO emission lines tell us that a large amount of large amount of molecular gasmolecular gas is present in this cluster M is present in this cluster Mgasgas = 8.5x10 = 8.5x101010 M Msun sun

(Edge 2001), which could be the gas cooled out from the flow (Edge 2001), which could be the gas cooled out from the flow during the CF during the CF

IT LOOKS LIKE A CLUSTER IT LOOKS LIKE A CLUSTER HARBOURING A STRONG COOLING HARBOURING A STRONG COOLING

FLOWFLOW

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rr cooli

ng

cooli

ng

Modelling the gas in A1068Modelling the gas in A1068

single temperature (wabs*mekal in single temperature (wabs*mekal in XSPEC)XSPEC)two temperature (wabs*(mekal+mekal) in two temperature (wabs*(mekal+mekal) in XSPEC)XSPEC)

comparison bet. 1T and other comparison bet. 1T and other models:models:as in the case of A2199 the single temperature model as in the case of A2199 the single temperature model

has good residuals, suggesting has good residuals, suggesting no need for other no need for other components components an eventual an eventual cool componentcool component in a 2T model should be no in a 2T model should be no cooler than cooler than 0.8 keV0.8 keV in the innermost bin. in the innermost bin.

according to the analysis in Wise according to the analysis in Wise et al.et al. (2004) we tried also (2004) we tried also with (old) CF model (wabs*(mekal+mkcflow) in XSPEC letting with (old) CF model (wabs*(mekal+mkcflow) in XSPEC letting the Tthe Tminmin be a free parameter together with mass dep. rate. be a free parameter together with mass dep. rate.

fits with CF model are very instable, however a fit on an fits with CF model are very instable, however a fit on an integrated spectrum (no annular bins!) suggest a integrated spectrum (no annular bins!) suggest a TTminmin of of about about 1.5 keV1.5 keV

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Let’s make the point on the second Let’s make the point on the second candidate!candidate!

again ... a good again ... a good candidate ...candidate ...

BUTBUTthe ICM is well described by a the ICM is well described by a 1T model1T model and and another another thermal componentthermal component, if present, , if present, cannot be cooler than cannot be cooler than ~ 0.8 keV~ 0.8 keV. Moreover . Moreover the the TTminmin of an eventual CF is no less than of an eventual CF is no less than 1.5 1.5 keVkeV!!

luminoluminoususlarge amount large amount of molecular of molecular

gas (Edge gas (Edge 2001)2001)

SOSO

NO CF IN A1068!!!NO CF IN A1068!!!

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We examined two objects that seemed We examined two objects that seemed perfect candidates to host a CF.perfect candidates to host a CF.

A2199 for the A2199 for the “relaxed aspect” “relaxed aspect”

and its high and its high luminosityluminosity

A1068 for the A1068 for the large amount of large amount of molecular gas molecular gas found by Edgefound by Edge

NEITHER IN A2199 NOR IN A1068 WE NEITHER IN A2199 NOR IN A1068 WE HAVE FOUND EVIDENCES FOR AN HAVE FOUND EVIDENCES FOR AN

ONGOING COOLING FLOW !!!ONGOING COOLING FLOW !!!


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