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XMM-Newton and Galaxy Clusters: from Cooling Flows to Cool Cores Silvano Molendi (IASF-MI)
XMM-Newton and Galaxy Clusters Silvano Molendi (IASF-MI)
Introduction This is a rapidly evolving research field. The new satellites are allowing us to make much progress. You may view this session as a sampler of the science we are now doing. Radial characterization of individual systems temperature (Pratt) mass (Pointecouteau), implications for cosmology (Arnaud). Study objects at unconcievable redshifts (Jones, Vauclair) Approach physical phenomena with an unprecedented combination of spectral and spatial capabilities (A. Finoguenov), mergers (J. L Sauvageot, Sakelliou).
Conclusions This is a very exciting time to be working on Clusters!
From Cooling-Flows to Cool Cores Silvano Molendi (IASF-MI)
Cooling Flows tcool ≈ Tg 1/2 np-1 • For large radii np is small • In the core np is large Э rcool tcool » t. Hubble tcool ~ t. Hubble The gas within rcool will cool and flow inwards
Key Issue The surface brightness is not as peaked as would be expected if all the cooling gas were to reach the center M≠const M r (Fabian, Nulsen & Canizares 1984) . . Most of the gas drops out the flow before reaching the center This has been explained in the context of multi-phase models (Nulsen 1986) Different phases T, ρ coexist at every r Multi-phase models require gas with T down to 0. 1 ke. V
The (XMM)-Newtonian Revolution
The RGS Result A 1795 Tamura et al. (2001 a); A 1835 Peterson et al. (2001); AS 1101 Kaastra et al. (2001); A 496 Tamura et al. (2001 b); sample of 14 objects Peterson et al. (2003) There is a remarkable lack of emission lines expected from gas with temperatures smaller than 1 -3 ke. V. The most straightforward interpretation is that there is no gas with temperatures smaller than 1 -3 ke. V. Standard CF model predicts gas with T down to at least 0. 1 ke. V!
The EPIC Result EPIC has a spectral resolution ~ 10 times worse than RGS. It cannot resolve individual lines. However it can discriminate between models with and without a minimum temperature The major discriminant is the Fe L Shell blend profile
Comparison between multi-temperature models Spectra above ~1. 3 ke. V are similar. Model spectra degraded to the EPIC resolution Below we observe a prominent line-like feature: Fe-L shell line complex. In the spectrum with Tmin=0. 1 ke. V we see a shoulder down to ~ 0. 8, this is due to low ionization lines from gas colder than 0. 9 ke. V. In the spectrum with Tmin=0. 9 ke. V the shoulder is absent because the low ionization lines are missing Tmin=0. 9 ke. V Tmin=0. 1 ke. V Molendi & Pizzolato (2001)
Minimum Temperature EPIC minimum temperatures are in good agreement with RGS minimum temperatures. The result on Tmin is a solid one! All cluster cores observed so far show a Tmin Values range between ~1 and ~3 ke. V
Spatially resolved spectroscopy of Cluster cores with EPIC M 87 Temperature map 1. In most of the core the gas is single temperature 2. The only regions where we find evidence of more than 1 temperature are the SW and E radio arms which are cospatial with the radio emission 3. No evidence of gas cooler than 1 ke. V Molendi (2002)
Implications for Cooling-Flow models Multiphaseness • Gas is NOT multiphase, at least not in the sense required by. the standard multi-phase CF model • Multiphaseness is or was a fundamental ingredient of the CF. model, without it the model falls! Mass deposition • Little evidence of gas cooler than 1 -3 ke. V anywhere • If gas does not cool below 1 -3 ke. V it will not be deposited as cold gas • Mass deposition, if there is any, must be much smaller than previously thought
Implications for Cooling-Flow models The name itself is missleading as it describes a phemoneon of little or no impact Cooling Flow Cool core
Now that we have brought the house down it is time to think about rebuilding!
Cool Cores What happens to the gas which should be cooling on very short timescales? Two classes of solutions have been proposed: The cooler gas is there but it is somehow hidden (Fabian et al. 2001) ✘ The gas is prevented from cooling below a certain temperature by some form of heating. Heating must be widespread as we do not observe accumulation of gas at a particular radius or temperature. Various mechanisms have been considered: thermal conduction (Narayan & Medvedev 2001, Fabian et al. 2002) Heating from the central AGN (e. g. Begelman 2002, Churazov et al. 2002)
Heating Mechanisms: Conduction • Determine the conduction coef. necessary to balance cooling and compare it to the Spitzer coefficent (Voigt et al. 2003, Ghizzardi et al. 2003) • Heating from conduction is insufficent within the very core. • Extra heating is required to balance cooling
Heating from the AGN Chandra finds what appear to be holes “cavities”. Hydra A Radio lobes are conicident with X-ray cavities Radio lobes inflated by jets appear to be making their way pushing aside the X-ray emitting plasma Mc. Namara et al. (2001)
Heating from the AGN Abell 2052 Blanton et al. (2001) Radio lobes fill X-ray cavities Cavities are surrounded by denser & cooler gas. If the lobes are responsible for heating the flow why are they surrounded by cool gas?
Heating from the AGN The total energy required to quench a flow can be considerable. Take total cooling energy, determined from L(< rcool ) • t. Hubble for a set of clusters and compare it with the total energy emitted by an AGN over t. Hubble. The more luminous cores imply very large black-hole masses Fabian et al. (2002)
Do we have a credible mechanism? From outside: The gas outside rcool is a huge heat reservoir, look for meachansim that tap this source (thermal conduction). From the AGN: 1) Interaction with Radio structures is localized 2) No evidence of heating at the site of the interaction (quite the contrary) 3) Heating could be episodic through outbursts of AGN activity, however we have various indicators that point to a gentle and non sporadic form of heating (e. g. Mathews & Brighenti 2003). 4) The overall energy available from the AGN may not be sufficent for the most massive systems.
Do we have a credible mechanism? Probably not The hunt is still on!
Looking for something better We need a form of widespread gentle heating. Something connected with subsonic gas motions would be nice. We do have evidence of widespread gas motions in the core of Perseus through the lack of Resonant Scattering (Gastaldello & Molendi 2003, Churazov et al. 2003) and detection of pressure waves (Fabian et al. 2003).
Summary Clusters are extremely interesting astrophys. objects. Amongst the most demanding from an instrumental point of view, it’s no wonder that innovative new satellites like Chandra and XMM-Newton are providing us with great new results Cooling Flows as we understood them in pre XMM-Newton days are dead! Currently we do not have a solid understanding of what keeps the gas from cooling, the answer may come in a week in a year or maybe 10 years from now