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

X-RAY SPECTRA: emission from optically thin thermal plasma polluted by heavy elements emission from optically thin thermal plasma polluted by heavy elements typical values: n e ~ – cm -3, T g ~ 10 7 – 10 8 K (heavily ionized gas), R ~ 1 Mpc. typical values: n e ~ – cm -3, T g ~ 10 7 – 10 8 K (heavily ionized gas), R ~ 1 Mpc. No absorption Exponential cut-off IMAGING: central regions feature ~ constant surface brightness central regions feature ~ constant surface brightness in outer regions S.B. falls off as a power-law with index ~ 3 in outer regions S.B. falls off as a power-law with index ~ 3 emission is traced out to 1-2 Mpc from the core emission is traced out to 1-2 Mpc from the core

Properties of the Intra Cluster Medium: hot, heavely ionized and tenouos gas at rest in the potential well of the cluster hot, heavely ionized and tenouos gas at rest in the potential well of the cluster dissipates energy at a very slow rate by X rays dissipates energy at a very slow rate by X rays considered as a fluid in hydrostatic equilibrium considered as a fluid in hydrostatic equilibrium

t cool ~ T g 1/2 n p -1 for large radii n p is small for large radii n p is small in the core n p is large in the core n p is large t cool << t Hubble t cool ~ t Hubble COOLING FLOW CLUSTERS surface brightness strongly peaked at the center surface brightness strongly peaked at the center low ionization lines in soft X-ray spectra low ionization lines in soft X-ray spectra temperature gradients toward the center temperature gradients toward the center Canizares et al. (1984) De Grandi & Molendi (2002)

In-homogenous model for CF (Nulsen 1984) multiphaseness of the gas: different phases (T and ρ) coexist, in pressure equilibrium (t sound < t cool ) at every r multiphaseness of the gas: different phases (T and ρ) coexist, in pressure equilibrium (t sound < t cool ) at every r the phases comove, under the pressure of the gas immediately on top, with << v sound. at T~10 6 K t cool ~ t sound : the cold blob decouples from the flow while the others continue to flow inward. at T~10 6 K t cool ~ t sound : the cold blob decouples from the flow while the others continue to flow inward. the mass deposition rate scales as r α, implyng that deposition occurs everywhere in the cooling flow region. Typical value for mass dep. rate: dM/dt=100M sun /yr the mass deposition rate scales as r α, implyng that deposition occurs everywhere in the cooling flow region. Typical value for mass dep. rate: dM/dt=100M sun /yr

cooling flows are seen in a large number of clusters (~ 60% - 70%), so they can be resonably considered as persistent phenomena Cold gas IONIZED NEUTRAL MOLECULAR lines observed in optical and UV indicate that ionized gas is present but << M acc 21 cm observations in central galaxies give M HI < 10 9 M sun recent observations (Edge 2002) have detected molecular gas for the first time, again << M acc

XMM point of view EPIC cannot resolve individual lines but can discriminate bet. models with and without a minimum temperature: In RGS spectra there is a remarkable lack of emission lines expected from gas cooling below 1-2 keV (see for example the sample of 14 objects in Petersen ) T min =0.9 keV: the shoulder is absent because the low ionization lines are missing. T min =0.9 keV: the shoulder is absent because the low ionization lines are missing. T min =0.1 keV: we see a shoulder down to ~ 0.8 keV, due to low ionization lines from gas colder than 0.9 keV. T min =0.1 keV: we see a shoulder down to ~ 0.8 keV, due to low ionization lines from gas colder than 0.9 keV.

both EPIC and RGS mesurements indicate T min in [1,3] keV standard cooling flow model predicts gas with T down to at least 0.1 keV! BUT gas is NOT multiphase, at least not in the sense required by the standard multi-phase CF model FAILURE OF THE STANDARD CF MODEL

If CFs are not observed something must quench them: HEATING MECHANISM feedback from AGN: Chandra observation clearly show interaction between AGN and the ICM (radio lobes/ X-ray cavities) feedback from AGN: Chandra observation clearly show interaction between AGN and the ICM (radio lobes/ X-ray cavities) Perseus (Fabian et al 2002) efficient mechanism only in cluster cores: too high M BH are required to completely quench a luminous CF (Fabian 2002) thermal conduction: large heat reservoir in the outer regions of clusters, if ΔT/T is large this mechanism should be efficient thermal conduction: large heat reservoir in the outer regions of clusters, if ΔT/T is large this mechanism should be efficient estimates of κ eff (r) show that this mechanism is efficient only in outermost regions: for innermost ones κ eff exceeds κ s (Ghizzardi et al. 2003) MIXED MODELS

First candidate: A2199 nearby cluster z = 0.030, D = Mpc (H 0 = 70 km/s/Mpc) nearby cluster z = 0.030, D = Mpc (H 0 = 70 km/s/Mpc) strong X-ray emission peaked on NGC6166: L X = 6.43 x erg/s strong X-ray emission peaked on NGC6166: L X = 6.43 x erg/s kT ~ 4.7 keV (Peres 1998), = 0.35 (De Grandi & Molendi 2001) kT ~ 4.7 keV (Peres 1998), = 0.35 (De Grandi & Molendi 2001) why A2199 is a good subject for our quest? extremely relaxed cluster, no evidence for azimuthal gradients in our kT and metallicity maps (XMM data) extremely relaxed cluster, no evidence for azimuthal gradients in our kT and metallicity maps (XMM data) lack of evidences for interaction bet. cD galaxy and ICM in Chandra images (sharper eyes than XMM-Newton) lack of evidences for interaction bet. cD galaxy and ICM in Chandra images (sharper eyes than XMM-Newton) very luminous in X band ( some erg/s) very luminous in X band ( some erg/s) IT LOOKS LIKE A CLUSTER HARBOURING A STRONG COOLING FLOW

r cooling spectral models applied to A2199: single temperature (wabs*mekal in XSPEC): 4 free parameters kT, redshift, abundance and normalization of the thermal component. single temperature (wabs*mekal in XSPEC): 4 free parameters kT, redshift, abundance and normalization of the thermal component. two temperature (wabs*(mekal+mekal) in XSPEC): two additional free parameters are T and normalization of the second component. two temperature (wabs*(mekal+mekal) in XSPEC): two additional free parameters are T and normalization of the second component. comparison bet. 1T and 2T models: 1T has good residuals, suggesting no need for other components 1T has good residuals, suggesting no need for other components we placed upper limits to the contribution of an eventual cool component: in the innermost region temperatures below 1.0 keV are ruled out, in the second bin ( arcmin) the value of T min rises up to 1.2 keV! we placed upper limits to the contribution of an eventual cool component: in the innermost region temperatures below 1.0 keV are ruled out, in the second bin ( arcmin) the value of T min rises up to 1.2 keV!

Let’s make the point on the first candidate! a promising cluster... BUT the ICM is well described by a 1T model. A second component, if present, cannot be cooler than ~ 1 keV (from spectral analysis) luminous luminous very relaxed very relaxed T and Z Fe gradients T and Z Fe gradients SO NO CF IN A2199!!!

Second candidate: A1068 more distant than A2199 z = , D = 645 Mpc (h 0 = 0.7) more distant than A2199 z = , D = 645 Mpc (h 0 = 0.7) X-ray emission peaked on cluster center X-ray emission peaked on cluster center kT ~ 4.0 keV, ~ 0.5 (Wise et al. 2004) kT ~ 4.0 keV, ~ 0.5 (Wise et al. 2004) why A1068 is a good subject for our quest? elliptical shape (ε = 0.71), complicated central morphology (r<50 kpc) elliptical shape (ε = 0.71), complicated central morphology (r<50 kpc) mesures of CO emission lines tell us that a large amount of molecular gas is present in this cluster M gas = 8.5x10 10 M sun (Edge 2001), which could be the gas cooled out from the flow during the CF mesures of CO emission lines tell us that a large amount of molecular gas is present in this cluster M gas = 8.5x10 10 M sun (Edge 2001), which could be the gas cooled out from the flow during the CF IT LOOKS LIKE A CLUSTER HARBOURING A STRONG COOLING FLOW

r cooling Modelling the gas in A1068 single temperature (wabs*mekal in XSPEC) single temperature (wabs*mekal in XSPEC) two temperature (wabs*(mekal+mekal) in XSPEC) two temperature (wabs*(mekal+mekal) in XSPEC) comparison bet. 1T and other models: as in the case of A2199 the single temperature model has good residuals, suggesting no need for other components as in the case of A2199 the single temperature model has good residuals, suggesting no need for other components an eventual cool component in a 2T model should be no cooler than 0.8 keV in the innermost bin. an eventual cool component in a 2T model should be no cooler than 0.8 keV in the innermost bin. according to the analysis in Wise et al. (2004) we tried also with (old) CF model (wabs*(mekal+mkcflow) in XSPEC letting the T min be a free parameter together with mass dep. rate. according to the analysis in Wise et al. (2004) we tried also with (old) CF model (wabs*(mekal+mkcflow) in XSPEC letting the T min be a free parameter together with mass dep. rate. fits with CF model are very instable, however a fit on an integrated spectrum (no annular bins!) suggest a T min of about 1.5 keV fits with CF model are very instable, however a fit on an integrated spectrum (no annular bins!) suggest a T min of about 1.5 keV

Let’s make the point on the second candidate! again... a good candidate... BUT the ICM is well described by a 1T model and another thermal component, if present, cannot be cooler than ~ 0.8 keV. Moreover the T min of an eventual CF is no less than 1.5 keV! luminous luminous large amount of molecular gas (Edge 2001) large amount of molecular gas (Edge 2001) SO NO CF IN A1068!!!

We examined two objects that seemed perfect candidates to host a CF. A2199 for the “relaxed aspect” and its high luminosity A1068 for the large amount of molecular gas found by Edge NEITHER IN A2199 NOR IN A1068 WE HAVE FOUND EVIDENCES FOR AN ONGOING COOLING FLOW !!!