Ubiquitous cold and massive filaments in cool core clusters
Valeria OlivaresP. SaloméF. CombesS. HamerP. GuillardM. D. LehnertF. L. PollesRicarda S. BeckmannYohan DuboisMegan DonahueA. C. EdgeA. C. FabianB. R. McNamaraT. RoseH. R. RussellG. TremblayA. N. VantyghemR. E. A. CanningG. J. FerlandB. GodardSébastien PeiraniG. Pineau des Forêts
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Multi-phase filamentary structures around Brightest Cluster Galaxies are likely a key step of AGN-feedback. We observed molecular gas in 3 cool cluster cores: Centaurus, Abell S1101, and RXJ1539.5 and gathered ALMA and MUSE data for 12 other clusters. Those observations show clumpy, massive and long, 3--25 kpc, molecular filaments, preferentially located around the radio bubbles inflated by the AGN (Active Galactic Nucleus). Two objects show nuclear molecular disks. The optical nebula is certainly tracing the warm envelopes of cold molecular filaments. Surprisingly, the radial profile of the H$\alpha$/CO flux ratio is roughly constant for most of the objects, suggesting that (i) between 1.2 to 7 times more cold gas could be present and (ii) local processes must be responsible for the excitation. Projected velocities are between 100--400 km s$^{-1}$, with disturbed kinematics and sometimes coherent gradients. This is likely due to the mixing in projection of several thin unresolved filaments. The velocity fields may be stirred by turbulence induced by bubbles, jets or merger-induced sloshing. Velocity and dispersions are low, below the escape velocity. Cold clouds should eventually fall back and fuel the AGN. We compare the filament's radial extent, r$_{fil}$, with the region where the X-ray gas can become thermally unstable. The filaments are always inside the low-entropy and short cooling time region, where t$_{cool}$/t$_{ff}$<20 (9 of 13 sources). The range t$_{cool}$/t$_{ff}$, 8-23 at r$_{fil}$, is likely due to (i) a more complex gravitational potential affecting the free-fall time (e.g., sloshing, mergers); (ii) the presence of inhomogeneities or uplifted gas in the ICM, affecting the cooling time. For some of the sources, r$_{fil}$ lies where the ratio of the cooling time to the eddy-turnover time, t$_{cool}$/t$_{eddy}$, is approximately unity.Keywords:
Submillimeter Array
Intracluster medium
Cooling flow
We use recent X-ray observations of the intracluster medium(ICM) of the galaxy group NGC 5813 to confront theoretical studies of ICM thermal evolution with the newly derived ICM properties.We argue that the ICM of the cooling flow in the galaxy group NGC 5813 is more likely to be heated by mixing of post-shock gas from jets residing in hot bubbles with the ICM,than by shocks or turbulentheating.Shocks thermalize only a small fraction of their energy in the inner regions of the cooling flow;in order to adequately heat the inner part of the ICM,they would overheat the outer regions by a large factor,leading to its ejection from the group.Heating by mixing,which was found to be much more efficient than turbulent-heating and shocks-heating,hence,rescues the outer ICM of NGC 5813 from its predestined fate according to cooling flow feedback scenarios that are based on heating by shocks.
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We use recent X-ray observations of the intracluster medium (ICM) of the galaxy group NGC 5813 to confront theoretical studies of ICM thermal evolution with the newly derived ICM properties. We argue that the ICM of the cooling flow in the galaxy group NGC 5813 is more likely to be heated by mixing of post-shock gas from jets residing in hot bubbles with the ICM, than by shocks or turbulent-heating. Shocks thermalize only a small fraction of their energy in the inner regions of the cooling flow; in order to adequately heat the inner part of the ICM, they would overheat the outer regions by a large factor, leading to its ejection from the group. Heating by mixing, which was found to be much more efficient than turbulent-heating and shocks-heating, hence, rescues the outer ICM of NGC 5813 from its predestined fate according to cooling flow feedback scenarios that are based on heating by shocks.
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We report the results of a detailed analysis of the temperature structure of the X-ray emitting plasma halo of M 87, the cD galaxy of the Virgo Cluster. Using the MEKAL model, the data provide strong indications that the intracluster medium has a single phase structure locally, except the regions associated with the radio structures. The deprojected spectrum at each radius is well fitted by a single temperature MEKAL model, except for the very central region (<2 arcmin) which seems to be affected by the jet and radio lobe structure. The temperature of the intracluster plasma is 1 keV at the center and gradually increases to 2.5 keV at 80 kpc. We have also fitted spectra using the APEC code. Although the large changes of the strength of Kα lines causes a discrepancy between the Fe-L and Fe-K lines for the APEC results, the overall temperature structure has not changed. There is no sign of excess absorption in the spectral data. The single-phase nature of the intracluster medium is in conflict with the standard cooling flow model which is based on a multi-phase temperature structure. In addition, the signature of gas cooling below 0.8 keV to zero temperature is not observed as expected for a cooling flow. The gravitational mass profile derived from the temperature and density distribution of the intracluster gas shows two distinct contributions that can be assigned to the gravitational potential of the cD galaxy and the cluster. The central temperature of the intracluster medium agrees well with the potential depth and the velocity dispersion of the cD galaxy. The latter result implies that the central region of the intracluster medium is equivalent to a virialized interstellar medium in M 87.
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We review observations on the chemical enrichment of the intracluster medium (ICM) performed using BeppoSAX MECS data. The picture emerging is that non-cooling flow clusters have flat metallicity profiles, whereas a strong enhancement in the abundance is found in the central regions of the cooling flow clusters. All the non-cooling flow clusters present evidence of recent merger activity suggesting that the merger events redistributes efficiently the metal content of the ICM. The observed abundance excess in the central regions of cooling flow clusters is probably due to metals ejected from the cD galaxy located in the cluster core. Cooling flow cluster have also enhanced Nickel abundances in their cores with respect to the non cooling flow clusters.
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Abstract The energy available from active galactic nuclei and their accompanying radio sources in clusters of galaxies have been suggested as energy sources that can solve the “cooling flow problem” in rich clusters of galaxies. In particular, fragmentation and subsequent mixing of buoyant radio source bubbles and relics has been proposed as a mechanism for mixing and reheating the intracluster medium. However, inclusion of the effects of the magnetic field present in the ICM of most clusters shows that the situation is more complex than might have been thought. Using self consistent 2‐D and 3‐D MHD calculations of the evolution of radio source bubbles in clusters, including their formation and including both galaxy and cluster gravitational potentials, it is shown that the buoyant bubbles are stable against fragmentation over times comparable to their buoyant risetimes and to the cooling times in clusters. In addition, lifting and mixing of the ICM is confined to volumes directly below the rising bubble and thus does not include an appreciable fraction of the overall volume of the ICM in the inner regions of clusters. Hence some additional mixing and fragmentation mechanisms may be required in order to effectively use radio sources in clusters as a means of general reheating of the ICM on times comparable in inner cluster cooling times. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
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It is generally argued that most clusters of galaxies host cooling flows in which radiative cooling in the center causes a slow inflow. However, recent observations by Chandra and XMM conflict with the predicted cooling flow rates. It has been suggested that radio jets that are situated at the center of clusters of galaxies can assist in reducing the deposition of cold gas. Radio jets inflate cavities of hot radio plasma that rise through the cluster atmosphere and thus stir the intracluster medium. In this Letter, we investigate whether this scenario is consistent with the pronounced metallicity gradients that have been observed in the cores of clusters.
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Over the past several years, numerous examples of X-ray cavities coincident with radio sources have been observed in so-called cool core clusters of galaxies. Motivated by these observations, we explore the evolution and the effect of cavities on a cooling intracluster medium (ICM) numerically, adding relevant physics step by step. In this paper we present a first set of hydrodynamical, high resolution (1024^3 effective grid elements), three-dimensional simulations, together with two-dimensional test cases. The simulations follow the evolution of radio cavities, modeled as bubbles filled by relativistic plasma, in the cluster atmosphere while the ICM is subject to cooling. We find that the bubble rise retards the development of a cooling flow by inducing motions in the ICM which repeatedly displace the material in the core. Even bubbles initially set significantly far from the cluster center affect the cooling flow, although much later than the beginning of the simulation. The effect is, however, modest: the cooling time is increased by at most only 25%. As expected, the overall evolution of pure hydrodynamic bubbles is at odds with observations, showing that some additional physics has to be considered in order to match the data.
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Aims. Over the past several years, numerous examples of X-ray cavities coincident with radio sources have been observed in so-called cool core clusters of galaxies. Motivated by these observations, we explore the evolution and the effect of cavities on a cooling intracluster medium (ICM) numerically, adding relevant physics step by step. Methods. In this paper we present a first set of hydrodynamical, high resolution (1024 3 effective grid elements), three-dimensional simulations, together with two-dimensional test cases. The simulations follow the evolution of radio cavities, modeled as bubbles filled by relativistic plasma, in the cluster atmosphere, while the ICM is subject to cooling. Results. We find that the bubble rise retards the development of a cooling flow by inducing motions in the ICM, which repeatedly displace the material in the core. Even bubbles initially set significantly far from the cluster center affect the cooling flow, although much later than the beginning of the simulation. The effect is, however, modest: the cooling time is increased by at most only 25%. As expected, the overall evolution of pure hydrodynamic bubbles is at odds with observations, showing that some additional physics has to be considered to match the data.
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Radiative Cooling
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We review observations on the chemical enrichment of the intracluster medium (ICM) performed using BeppoSAX MECS data. The picture emerging is that non-cooling flow clusters have flat metallicity profiles, whereas a strong enhancement in the abundance is found in the central regions of the cooling flow clusters. All the non-cooling flow clusters present evidence of recent merger activity suggesting that the merger events redistributes efficiently the metal content ofthe ICM. The observed abundance excess in the central regions of cooling flow clusters is probably due to metals ejected from the cD galaxy located in the cluster core. Cooling flow cluster have also enhanced Nickel abundances in their cores with respect to the non cooling flow clusters.
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ABSTRACT We present the discovery of a giant ≳100 kpc Ly α nebula detected in the core of the X-ray emitting cluster CL J1449+0856 at z = 1.99 through Keck/LRIS narrow-band imaging. This detection extends the known relation between Ly α nebulae and overdense regions of the universe to the dense core of a 5–7 × 10 13 M ⊙ cluster. The most plausible candidates to power the nebula are two Chandra -detected AGN host cluster members, while cooling from the X-ray phase and cosmological cold flows are disfavored primarily because of the high Ly α to X-ray luminosity ratio ( L Ly &agr; / L X ≈ 0.3 -->?> , ≳10–1000 times higher than in local cool-core clusters) and by current modeling. Given the physical conditions of the Ly α -emitting gas and the possible interplay with the X-ray phase, we argue that the Ly α nebula would be short-lived (≲10 Myr) if not continuously replenished with cold gas at a rate of ≳1000 M ⊙ yr −1 . We investigate the possibility that cluster galaxies supply the required gas through outflows and we show that their total mass outflow rate matches the replenishment necessary to sustain the nebula. This scenario directly implies the extraction of energy from galaxies and its deposition in the surrounding intracluster medium (ICM), as required to explain the thermodynamic properties of local clusters. We estimate an energy injection of the order of ≈ 2 keV -->?> per particle in the ICM over a 2 Gyr interval. In our baseline calculation, AGNs provide up to 85% of the injected energy and two-thirds of the mass, while the rest is supplied by supernovae-driven winds.
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