Thermal conduction and reduced cooling flows in galaxy clusters

Abstract

Conduction may play an important role in reducing cooling flows in galaxy clusters. We analyse a sample of sixteen objects using Chandra data and find that a balance between conduction and cooling can exist in the hotter clusters (T > 5 keV), provided the plasma conductivity is close to the unhindered Spitzer value. In the absence of any additional heat sources, a reduced mass inflow must develop in the cooler objects in the sample. We fit cooling flow models to deprojected data and compare the spectral mass deposition rates found to the values required to account for the excess luminosity, assuming Spitzer-rate heat transfer over the observed temperature gradients. The mass inflow rates found are lower than is necessary to maintain energy balance in at least five clusters. However, emission from cooling gas may be partially absorbed. We also compute the flux supplied by turbulent heat transport (Cho et al. 2003) and find conductivity profiles which follow a strikingly similar temperature dependence to the conductivity values required to prevent cooling. Finally, we show that the cluster radio luminosities vary by over five orders of magnitude in objects with X-ray luminosities differing by no more than a factor of a few. This suggests that there is unlikely to be a straightforward correlation between the mechanical power provided by the radio lobes and the rate of energy loss in cooling flow clusters.Comment: Submitted to MNRA

Interplay Among Cooling, Agn Feedback, and Anisotropic Conduction in the Cool Cores of Galaxy Clusters

“…Therefore, the relative importance of conductive to AGN heating is largely determined by the temperature profile and the mass of the clusters. Previous works have tried to evaluate the importance of conductive heating from the observed profiles of clusters assuming one-third of Spitzer conductivity (e.g., Voigt & Fabian 2004;Voit 2011). Our results suggest that there indeed exists a quasi-steady thermal balance among cooling, AGN feedback, and conduction (Voit 2011), and the contributions from conduction and AGN heating derived from such observations should not vary more than a factor of a few over the course of the cluster evolution once their cores have reached such a quasi-equilibrium stage.…”

“…First, thermal conduction has the potential to be extremely important for the thermodynamic state of a CC (e.g., Voigt & Fabian 2004;Voit 2011). While it cannot by itself offset the radiative cooling in a stable manner (Stewart et al 1984;Bregman & David 1988;Soker 2003;Zakamska & Narayan 2003;Voigt & Fabian 2004;Pope et al 2006), it may provide part of the heating, reducing the burden on the AGN, and can aid in the isotropization of the AGN heating throughout the core. Second, the ICM is known to be magnetized with β∼100 (Carilli & Taylor 2002), where β is defined as the ratio between gas thermal pressure and magnetic pressure.…”

STAR-FORMING BRIGHTEST CLUSTER GALAXIES AT 0.25 < z < 1.25: A TRANSITIONING FUEL SUPPLY

“…This has led to the conclusion that star formation is fueled in the BCG by residual cooling flows (Voigt & Fabian 2004;Tremblay et al 2012;McDonald et al 2014b). In order to test whether this trend was established at high-z, we require estimates of the core entropy and cooling rate for each cluster.…”

“…In order to test whether this trend was established at high-z, we require estimates of the core entropy and cooling rate for each cluster. Given that we only have ∼2000 X-ray counts per cluster, modeling the central entropy (e.g., Cavagnolo et al 2009) or estimating the spectroscopically derived cooling rate (e.g., Voigt & Fabian 2004) is not feasible. Instead, we compute spectroscopic quantities (bolometric luminosity, temperature) from a circular aperture with a radius of 0.075 R 500 (where R 500 was derived based on the Y X -M 500 relation of Vikhlinin et al 2009), which should roughly correspond to the deprojected core temperature (see e.g., McDonald et al 2014a).…”

An overview of jet-mode AGN feedback and the prospects for studying its cosmic evolution with LOFAR

“…conduction (Zakamska & Narayan 2003;Voigt & Fabian 2004), turbulent mixing (Kim & Narayan 2003), mergers (Gómez et al 2002), sloshing (ZuHone et al 2010), SN (Domainko et al 2004), turbulence energy triggered by SF and SN (FalcetaGonçalves et al 2010;de Gouveia Dal Pino et al 2011), and gravitational heating from clumpy accretion (Dekel & Birnboim 2008).…”