X-ray surface brightness and gas density fluctuations in the Coma cluster

Non-thermal pressure from turbulence and bulk flows is a fundamental ingredient in hot gaseous halos, and in the intracluster medium it will be measured through emission line kinematics with calorimeters on future X-ray spacecraft. In this paper we present a complementary method for measuring these effects, using forbidden FUV emission lines of highly ionized Iron which trace 10 7 K gas. The brightest of these is [Fe xxi] λ1354.1. We search for these lines in archival HST-COS spectra from the well-known elliptical galaxies M87 and NGC4696, which harbor large reservoirs of 10 7 K gas. We report a 2.2σ feature which we attribute to [Fe xxi] from a filament in M87, and positive residuals in the nuclei of M87 and NGC4696, for which the 90% upper limits on the line flux are close to the predicted fluxes based on X-ray observations. In a newer reduction of the data from the Hubble Spectroscopic Legacy Archive, these limits become tighter and the [Fe xxi] feature reaches a formal significance of 5.3σ, neglecting uncertainty in fitting the continuum. Using our constraints, we perform emission measure analysis, constraining the characteristic path length and column density of the ∼ 10 7 K gas. We also examine several sightlines towards filaments or cooling flows in other galaxy clusters, for which the fraction of gas at 10 7 K is unknown, and place upper limits on its emission measure in each case. A mediumresolution HST-COS observation of the M87 filament for ∼10 orbits would confirm our detection of [Fe xxi] and measure its width.

Section: Discussionmentioning

confidence: 99%

Searching for FUV line emission from 10⁷ K gas in massive elliptical galaxies and galaxy clusters as a tracer of turbulent velocities

Anderson

Sunyaev

2016

“…ATHENA) should be able eventually to detect directly the driving-scale turbulent motions in the ICMs of multiple clusters (Nagai et al 2013;Ettori et al 2013;Zhuravleva et al 2013;). In the meantime, turbulent motions in the ICM induce moderate pressure fluctuations that may be detected in X-rays (e.g., Schuecker et al 2004;Sanders & Fabian 2012;Churazov et al 2012;Gaspari et al 2014;Zhuravleva et al 2014), or through the S-Z effect (e.g., Khatri & Gaspari 2016). …”

Section: Discussionmentioning

confidence: 99%

Turbulence and vorticity in Galaxy clusters generated by structure formation

Vazza

Jones

Brüggen

et al. 2016

111

148

Turbulence is a key ingredient for the evolution of the intracluster medium, whose properties can be predicted with high resolution numerical simulations. We present initial results on the generation of solenoidal and compressive turbulence in the intracluster medium during the formation of a small-size cluster using highly resolved, non-radiative cosmological simulations, with a refined monitoring in time. In this first of a series of papers, we closely look at one simulated cluster whose formation was distinguished by a merger around z ∼ 0.3. We separate laminar gas motions, turbulence and shocks with dedicated filtering strategies and distinguish the solenoidal and compressive components of the gas flows using Hodge-Helmholtz decomposition. Solenoidal turbulence dominates the dissipation of turbulent motions (∼ 95%) in the central cluster volume at all epochs. The dissipation via compressive modes is found to be more important (∼ 30% of the total) only at large radii ( 0.5 r vir ) and close to merger events. We show that enstrophy (vorticity squared) is good proxy of solenoidal turbulence. All terms ruling the evolution of enstrophy (i.e. baroclinic, compressive, stretching and advective terms) are found to be significant, but in amounts that vary with time and location. Two important trends for the growth of enstrophy in our simulation are identified: first, enstrophy is continuously accreted into the cluster from the outside, and most of that accreted enstrophy is generated near the outer accretion shocks by baroclinic and compressive processes. Second, in the cluster interior vortex stretching is dominant, although the other terms also contribute substantially.

“…Equation (8) essentially provides an estimate of the conventional cross power spectrum [equation (7)] convolved with a smoothing kernel (see, e.g., Arévalo et al 2012;Churazov et al 2012;, for details). Measuring power spectra P k,aa and P k,bb in both bands and the cross spectrum P k,ab , a scaledependent correlation coefficient (coherence),…”

Section: Isobaric Adiabatic and Isothermal Fluctuationsmentioning

confidence: 99%

The nature and energetics of AGN-driven perturbations in the hot gas in the Perseus Cluster

Zhuravleva

Churazov

Arévalo

et al. 2016

Self Cite

Cores of relaxed galaxy clusters are often disturbed by AGN. Their Chandra observations revealed a wealth of structures induced by shocks, subsonic gas motions, bubbles of relativistic plasma, etc. In this paper, we determine the nature and energy content of gas fluctuations in the Perseus core by probing statistical properties of emissivity fluctuations imprinted in the soft-and hard-band X-ray images. About 80 per cent of the total variance of perturbations on ∼ 8 − 70 kpc scales in the inner region have an isobaric nature, i.e., are consistent with slow displacements of the gas in pressure equilibrium with ambient medium. Observed variance translates to the ratio of nonthermal to thermal energy of ∼ 13 per cent. In the region dominated by weak "ripples", about half of the total variance is also associated with isobaric perturbations on scales a few tens of kpc. If these isobaric perturbations are induced by buoyantly rising bubbles, then these results suggest that most of the AGN-injected energy should first go into bubbles rather than into shocks. Using simulations of a shock propagating through the Perseus atmosphere, we found that models reproducing the observed features of a central shock have more than 50 per cent of the AGN-injected energy associated with the bubble enthalpy and only about 20 per cent is carried away with the shock. Such energy partition is consistent with the AGN-feedback model, mediated by bubbles of relativistic plasma, and supports the importance of turbulence in the balance between gas heating and radiative cooling.