The impact of mergers on relaxed X-ray clusters – I. Dynamical evolution and emergent transient structures

By Gregory B. Poole, Mark A. Fardal, Arif Babul, Ian G. McCarthy, Thomas R. Quinn, James Wadsley. 2006

221 citations recorded by the source corpus.

We report on the analysis of a suite of smoothed particle hydrodynamics simulations (incorporating cooling and star formation) of mergers involving idealized X-ray clusters whose initial conditions resemble relaxed clusters with cool compact cores observed by Chandra and XMM. The simulations sample the most-interesting, theoretically plausible, range of impact parameters and progenitor mass ratios. We find that all mergers evolve via a common progression. We illustrate this progression in the projected gas density, X-ray surface brightness, Sunyaev-Zel'dovich, temperature, and gas-entropy maps. Several different classes of transient 'cold front' like features can arise over the course of a merger. Each class is distinguished by a distinct morphological signature and physical cause. We find that all these classes are present in Chandra and XMM observations of merging systems and propose a naming scheme for these features: 'comet-like' tails, bridges, plumes, streams and edges. In none of the cases considered do the initial cool compact cores of the primary and the secondary get destroyed during the course of the mergers. Instead, the two remnant cores eventually combine to form a new core that, depending on the final mass of the remnant, can have a greater cooling efficiency than either of its progenitors. We quantify the evolving morphology of our mergers using centroid variance, power ratios and offset between the X-ray and the projected mass maps. We find that the centroid variance best captures the dynamical state of the cluster. It also provides an excellent indicator of how far the system is from virial and hydrostatic equilibrium. Placing the system at z = 0.1, we find that all easily identified observable traces of the secondary disappear from a simulated 50-ks Chandra image following the second pericentric passage. The system, however, takes an additional ∼2 Gyr to relax and virialize. Observationally, the only reliable indicator of a system in this state is the smoothness of its X-ray surface brightness isophotes, not temperature fluctuations. Temperature fluctuations at the level of AT/T ∼20 per cent, can persist in the final systems well past the point of virialization, suggesting that the existence of temperature fluctuations, in and of themselves, does not necessarily indicate a disturbed or unrelaxed system.

Subfields: Astronomy and Astrophysics

View Paper: https://www.semanticscholar.org/paper/ade59e369f96e9b34198d98b439a4eed7ec4542a

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Citations in the corpus

The mass–concentration–redshift relation of cold and warm dark matter haloes (2016, background): “Furthermore, since DM haloes are not truly isolated, the virial ratio should be corrected for external forces and surface pressure terms (see e.g. Poole et al. 2006; Knebe & Power 2008; Klypin et al. 2016, for a discussion) and only then can it be used to meaningfully assess departures from…”
Lensing and x-ray mass estimates of clusters (simulations) (2012, unknown): “Following Poole et al. (2006) and Maughan et al. (2008), we define the centroid-shift as w = 1 Rmax × √∑ i(∆i − 〈∆〉)2 (N − 1) , (10) where Rmax is the radius of the largest aperture, and ∆i = ~Rc,i − ~Rc,max is the shift of the centroid in the i−th aperture with respect to the centroid in the…”
Searching for cool core clusters at high redshift (2008, background): “However, an analysis of smoothed particle hydrodynamics simulations of X-ray cluster mergers by Poole et al. 2006, suggests that the heating of the ICM arising from mergers is not sufficient to prevent cooling.”
Evidence for non-hydrostatic gas from the cluster X-ray to lensing mass ratio (2007, background): “This agrees with N-body simulations showing that the existence of a cool core is not a reliable predictor of the equilibrium state of a cluster of galaxies (e.g. Poole et al. 2006, 2007; Burns et al. 2007).”
JOINT ANALYSIS OF CLUSTER OBSERVATIONS. II. CHANDRA/XMM-NEWTON X-RAY AND WEAK LENSING SCALING RELATIONS FOR A SAMPLE OF 50 RICH CLUSTERS OF GALAXIES (2012, methodology): “We refer the reader to Buote & Tsai (1995), Poole et al. (2006), Jeltema et al. (2005), Jeltema et al. (2008), and Böhringer et al. (2010) for details on the calculation of these estimators.”
A Dark Core in Abell 520 (2007, background): “This offset is expected for ram pressure stripping, and is seen in gas+dark matter simulations of merging clusters (Poole et al. 2006).”
Ram pressure stripping the hot gaseous haloes of galaxies in groups and clusters (2007, background): “…being accreted is in small dense “lumps” (e.g., low-mass virialised systems, as in the present case), it can penetrate all the way to the core of the massive system without being significantly shocked (e.g., Motl et al. 2004; Murray & Lin 2004; Poole et al. 2006; M07; Dekel & Birnboim 2007).”
LoCuSS: comparison of observed X-ray and lensing galaxy cluster scaling relations with simulations (2008, background): “For example, the temperatures of merging clusters can be boosted (Smith et al. 2005; Poole et al. 2006, 2007).”
Gas expulsion by quasar-driven winds as a solution to the overcooling problem in galaxy groups and clusters (2010, methodology): “As for mergers being an explanation for NCC clusters, Poole et al. (2006, 2008) used high-resolution SPH simulations of cluster mergers to show that the dense, low-entropy gas in the cores of clusters is generally robust to mergers (although see Mitchell et al. 2009; ZuHone 2010 who argued that SPH…”
ON THE CONNECTION BETWEEN GIANT RADIO HALOS AND CLUSTER MERGERS (2010, methodology): “Following the method of Poole et al. (2006) and Maughan et al. (2008), the centroid shift is computed in a series of circular apertures centered on the cluster X-ray peak.”
STIRRING UP THE POT: CAN COOLING FLOWS IN GALAXY CLUSTERS BE QUENCHED BY GAS SLOSHING? (2009, methodology): “Such simulations have been employed in many previous works, typically in order either to explore a parameter space of mergers (e.g., Ricker & Sarazin 2001; Poole et al. 2006, 2007) or to simulate specific cluster merger scenarios (e.g., Springel & Farrar 2007; ZuHone et al. 2009).”
The cool-core bias in X-ray galaxy cluster samples - I. Method and application to HIFLUGCS (2010, background): “(15) From the simulations of Poole et al. (2006), it appears that clusters require in average a timescale of ∼ 5 Gyr to relax from a merging event.”
Images, Structural Properties, and Metal Abundances of Galaxy Clusters Observed with Chandra ACIS-I at 0.1 < z < 1.3 (2007, methodology): “Centroid shifts were measured following the method of Poole et al. (2006).”
Galaxy-cluster gas-density distributions of the Representative XMM-Newton Cluster Structure Survey (REXCESS) (2008, methodology): “D surface brightness distribution as means of characterising the cluster dynamical state: the power ratio method of Buote & Tsai (1995) and centre shifts (e.g. Mohr et al. 1995, Poole et al. 2006).”
Diffuse Optical Light in Galaxy Clusters. II. Correlations with Cluster Properties (2007, background): “In a simulation of 9 cluster mergers with mass ratios ranging from 1:1 to 10:1 with a range of orbital properties, Poole et al. (2006) show that clusters are virialized at or shortly after they visually appear relaxed through the absence of structures (clumps, shocks, cavities) or centroid shifts…”