Off-Axis Cluster Mergers: Effects of a Strongly Peaked Dark Matter Profile

By Paul M. Ricker, C. Sarazin. 2001

352 citations recorded by the source corpus.

We present a parameter study of offset mergers between clusters of galaxies. Using the Eulerian hydrodynamics/N-body code COSMOS, we simulate mergers between nonisothermal, hydrostatic clusters with a steep central dark matter density profile and a β-model gas profile. We constrain global properties of the model clusters using observed cluster statistical relationships. We consider impact parameters between 0 and 5 times the dark matter scale radius and mass ratios of 1 : 1 and 1 : 3. The morphological changes, relative velocities, and temperature jumps we observe agree with previous studies using the King profile for the dark matter. We observe a larger jump in X-ray luminosity (~4-10 times) than in previous work, and we argue that this increase is most likely a lower limit due to our spatial resolution. We emphasize that luminosity and temperature jumps due to mergers may have an important bearing on constraints on Ω derived from the observation of hot clusters at high redshift. Shocks are relatively weak in the cluster cores; hence, they do not significantly increase the entropy there. Instead, shocks create entropy in the outer regions, and this high-entropy gas is mixed with the core gas during later stages of the merger. Ram pressure initiates mixing by displacing the core gas from its potential center, causing it to become convectively unstable. The resulting convective plumes produce large-scale turbulent motions with eddy sizes up to several hundred kiloparsecs. This turbulence is pumped by dark matter-driven oscillations in the gravitational potential. Even after nearly a Hubble time these motions persist as subsonic turbulence in the cluster cores, providing 5%-10% of the support against gravity. The dark matter oscillations are also reflected in the extremely long time following a merger required for the remnant to reach virial equilibrium.

Subfields: Astronomy and Astrophysics, Instrumentation

View Paper: https://www.semanticscholar.org/paper/db11d4c9333d454d3a6c49030f21002e59461acd

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THE ATACAMA COSMOLOGY TELESCOPE: ACT-CL J0102−4915 “EL GORDO,” A MASSIVE MERGING CLUSTER AT REDSHIFT 0.87 (2011, background): “A number of groups (e.g., Ricker & Sarazin 2001; Randall et al. 2002) have shown that cluster mergers can result in a transient boost in X-ray temperaure and luminosity during a merger, compared to the X-ray emission of the merged cluster once it relaxes.”
Evolving turbulence and magnetic fields in galaxy clusters (2005, methodology): “It is likely that intense random vortical flows, if not turbulence, are produced in the merger events (Kulsrud et al. 1997; Norman & Bryan 1999; Ricker & Sarazin 2001).”
Turbulent Motions and Shocks Waves in Galaxy Clusters simulated with AMR (2009, background): “Early Eulerian numerical simulations of merging clusters (e.g., Bryan & Norman 1998; Ricker & Sarazin 2001) provided the first reliable representations of the way in which turbulence ID Ngrid Mdm [M⊙/h] ∆ [kpc] AMR v256-4 2563 6.76 · 108 18 D+V(δ > 10) v256-3 2563 6.76 · 108 36 D+V(δ > 3) v128-3…”
Planck 2013 results. XX. Cosmology from Sunyaev-Zeldovich cluster counts (2013, background): “This may be due to the relatively short duration of the shocking phase during a merger (e.g., Ricker & Sarazin 2001; Ritchie & Thomas 2002; Poole et al. 2007).”
Massive and refined - II. The statistical properties of turbulent motions in massive galaxy clusters with high spatial resolution (2010, background): “Early Eulerian numerical simulations of merging clusters (e.g., Roettiger, Stone & Burns 1999; Norman & Bryan 1999; Ricker & Sarazin 2001) obtained the ﬁrst reliable representation of the way in which turbulence is injected into the ICM by merger events.”
The X-Ray Luminosity-Mass Relation for Local Clusters of Galaxies (2006, result): “This finding may seem at odds with results from binary merger simulations by Ricker & Sarazin (2001).”
Constrained Simulations of the Real Universe. II. Observational Signatures of Intergalactic Gas in the Local Supercluster Region (2001, background): “The merger results in residual chaotic gas motions (Norman & Bryan 1999a), which homogenize entropy of the gas in the central regions via ‘‘ turbulent ’’ mixing (see, e.g., controlled cluster merger experiments of Ricker & Sarazin 2001).”
On the efficiency and reliability of cluster mass estimates based on member galaxies (2006, background): “In clusters undergoing merging events the X-ray luminosity and temperature can be boosted, thus leading to an overestimate of the cluster mass (e.g. Schindler & Müller 1993; Ricker & Sarazin 2001; Barrena et al. 2002; Diaferio et al. 2005).”
Galaxy cluster X-ray luminosity scaling relations from a representative local sample (REXCESS) (2008, background): “…shown that while major mergers can indeed boost both luminosity and temperature, the boosting appears to be short lived and the net movement in the luminosity temperature plane is approximately parallel to the mean relation (Ricker & Sarazin 2001; Ritchie & Thomas 2002; Hartley et al. 2008).”
X-ray spectroscopy of galaxy clusters: studying astrophysical processes in the largest celestial laboratories (2009, background): “The barlike hot region to the NE is interpretated as the signature of an off-axis merger at a stage short after the first close encounter similar to features observed in simulations (Belsole et al. 2005; Ricker and Sarazin 2001).”
Moving mesh cosmology: the hydrodynamics of galaxy formation (2011, result): “This test is similar in spirit to a number of previous works which analysed collisions of two galaxy clusters in isolation (see e.g. Ricker & Sarazin 2001; Ritchie & Thomas 2002; McCarthy et al. 2007; Springel & Farrar 2007; Mitchell et al. 2009; ZuHone 2011), but here we devise a cleaner set-up in…”
Astrophysical magnetic fields and nonlinear dynamo theory (2004, background): “Similar peculiar gas motions have also been 25 found in other numerical simulations of cluster formation [554] and cluster mergers [552].”
Resolving the Formation of Protogalaxies. I. Virialization (2007, background): “The second happens when minor and major mergers create Kelvin-Helmholtz instabilities and drives additional turbulence (e.g. Ricker & Sarazin 2001; Takizawa 2005).”
A systematic study of X-ray substructure of galaxy clusters detected in the ROSAT All-Sky Survey ? (2001, background): “Moreover, mergers affect cluster X-ray luminosity, magnetic field, and electron/ion non-equipartition (see, e.g., Schindler & Müller 1993; Roettiger et al. 1999, Takizawa 2000, Ricker & Sarazin 2001).”
AGN heating and ICM cooling in the HIFLUGCS sample of galaxy clusters (2008, background): “However, merging clusters present the same bias as cluster merger events entail temporal enhancements in the global luminosities and temperatures (Ricker & Sarazin 2001).”
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).”
Cosmological constraints from the local X-ray luminosity function of the most X-ray-luminous galaxy clusters (2002, background): “Ricker & Sarazin (2001), Ritchie & Thomas (2002) and Randall, Sarazin & Ricker (2002) present simulations of the effects of mergers on the X-ray properties of clusters for a variety of mass ratios, impact parameters and central gas densities.”
Compressible turbulence in galaxy clusters: physics and stochastic particle re-acceleration (2007, background): “…merging clusters provide an insight into the gas dynamics during a merger event (e.g., Roettiger, Burns, Loken 1996; Roettiger, Loken, Burns 1997; Ricker & Sarazin 2001): sub–clusters generate laminar bulk flows through the sweeped volume of the main clusters which inject turbulence via e.g.…”