A dynamical model for the distribution of dark matter and gas in galaxy clusters

By E. Rasia, G. Tormen, L. Moscardini. 2003

222 citations recorded by the source corpus.

Using the results of an extended set of high-resolution non-radiative hydrodynamic simulations of galaxy clusters, we obtain simple analytic formulae for the dark matter and hot gas distribution, in the spherical approximation. Starting from the dark matter phase-space radial density distribution, we derive fits for the dark matter density, velocity dispersion and velocity anisotropy. We use these models to test the dynamical equilibrium hypothesis through the Jeans equation: we find that this is satisfied to good accuracy by our simulated clusters inside their virial radii. This result also shows that our fits constitute a self-consistent dynamical model for these systems. We then extend our analysis to the hot gas component, obtaining analytic fits for the gas density, temperature and velocity structure, with no further hypothesis on the gas dynamical status or state equation. Gas and dark matter show similar density profiles down to ≈0.06Rv (with Rv the virial radius), while at smaller radii the gas flattens, producing a central core. Gas temperatures are almost isothermal out to roughly 0.2 Rv, then steeply decrease, reaching at the virial radius a value almost a factor of 2 lower. We find that the gas is not at rest inside Rv: velocity dispersions are increasing functions of the radius, motions are isotropic to slightly tangential, and contribute non-negligibly to the total pressure support. We test this model using a generalization of the hydrostatic equilibrium equation, where the gas motion is properly taken into account. Again we find that the fits provide an accurate description of the system: the hot gas is in equilibrium and is a good tracer of the overall cluster potential if all terms (density, temperature and velocity) are taken into account, while simpler assumptions cause systematic mass underestimates. In particular, we find that using the so-called β-model underestimates the true cluster mass by up to 50 per cent at large radii. We also find that, if gas velocities are neglected, then a simple isothermal model fares better at large radii than a non-isothermal one. The shape of the gas density profile at small radii is at least partially explained by the gas expansion caused by energy transfer from dark matter during the collapse. In fact, when gas bulk energy is also considered, gas and dark matter are in energy equipartition in the final system at radii r > 0.1Rv, while at smaller radii the gas is hotter than the dark matter. This energy imbalance is also probably the reason of the further global halo compression compared with a pure collisionless collapse, which we point out by comparing the dark matter and total density profiles of our hydro-simulated clusters with a set of identical – but pure N-body – ones. The compression has the effect of raising the mean concentration by an amount of roughly 10 per cent.

Subfields: Astronomy and Astrophysics, Statistical and Nonlinear Physics

View Paper: https://www.semanticscholar.org/paper/98046f9815e17e4c62e26b17ea041b26a7932739

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Citations in the corpus

The Influence of Baryons on the Clustering of Matter and Weak-Lensing Surveys (2005, background): “…1.5, respectively.zs The dashed lines are the predictions from our nonradiative run, while the solid lines give the results for the star formation run. temperature in the central regions of dark halos, because of its collisional nature (see Rasia et al. 2004; W. P. Lin et al. 2006, in preparation).”
Massive and refined - II. The statistical properties of turbulent motions in massive galaxy clusters with high spatial resolution (2010, background): “…regions of galaxy clusters is an important issue because all estimates of cluster masses derived by X-ray observables are a ﬀ ected by the presence of non-thermal pressure support at some level (Rasia et al. 2004; Lau et al. 2008; Pi ﬀ aretti & Valdarnini 2008; Burns, Skillman & O’Shea 2010).”
IMPACT OF CLUSTER PHYSICS ON THE SUNYAEV–ZEL'DOVICH POWER SPECTRUM (2010, methodology): “…simulations have demonstrated that a significant fraction of the total energy of the ICM is contained within random gas motions, which provide a significant non-thermal contribution to the total pressure support (Evrard 1990; Rasia et al. 2004; Kay et al. 2004; Dolag et al. 2005; Lau et al. 2009).”
On the efficiency and reliability of cluster mass estimates based on member galaxies (2006, background): “…of the condition of hydrostatic equilibrium, inaccurate modelling of the gas density profile and observational biases in the measure of the intra–cluster gas temperature, may lead to a sizeable underestimate of the cluster mass (e.g. Bartelmann & Steinmetz 1996; Kay et al. 2004; Rasia et al. 2004).”
ON THE CLUSTER PHYSICS OF SUNYAEV–ZEL'DOVICH AND X-RAY SURVEYS. I. THE INFLUENCE OF FEEDBACK, NON-THERMAL PRESSURE, AND CLUSTER SHAPES ON Y–M SCALING RELATIONS (2011, background): “NON-THERMAL CLUSTER PROFILES Several simulations (Evrard 1990; Rasia et al. 2004; Lau et al. 2009) showed that the kinetic pressure from bulk motions contributes a small but still significant amount of energy withinR500 and this importance increases for larger cluster radii (Lau et al. 2009;…”
Cosmological Simulations with Self-Interacting Dark Matter I: Constant Density Cores and Substructure (2012, methodology): “By noting that vrms,CDM(r) = (ρCDM(r)/Q(r)) 1/3 and using a phase-space density profileQ(r) = Q(rs)(r/rs)−η (Taylor & Navarro 2001; Rasia et al. 2004; Ascasibar et al. 2004; Dehnen & McLaughlin 2005; Ascasibar & Gottlöber 2008), we may fully specify thedependence ofr1 on the cross-section and halo…”
Dark matter in elliptical galaxies — II. Estimating the mass within the virial radius (2004, background): “Note that the orbital anisotropies of Diaferio (1999), Col´ın et al. (2000), and Wojtak et al. (2005) include the mean radial and tgential streaming motions, while that of Rasia et al. (2004)does not.”
Weighing simulated galaxy clusters using lensing and X-ray (2009, result): “This mass is compared to the true mass Mtrue as in Rasia et al. (2004).”
GALAXY CLUSTERS SELECTED WITH THE SUNYAEV–ZEL'DOVICH EFFECT FROM 2008 SOUTH POLE TELESCOPE OBSERVATIONS (2010, methodology): “The mass dependence of their pressure profile was determined using cluster mass estimates derived from the equation of hydrostatic equilibrium; simulations suggest that this method may underestimate the true mass by 10%–20% (Rasia et al. 2004; Meneghetti et al. 2010; Lau et al. 2009).”
Systematics in the X-ray cluster mass estimators (2006, methodology): “Rasia et al. (2004) suggested that in order to correctly compute the total mass, the gas velocity has to be taken into account, because it is a relevant component of the total energy equipartition between gas and DM.”
ERRATUM: “CHANDRA SAMPLE OF NEARBY RELAXED GALAXY CLUSTERS: MASS, GAS FRACTION, AND MASS–TEMPERATURE RELATION” (2006, ApJ, 640, 691) (2005, background): “A detailed study of these effects will be presented in D. Nagai et al. (2006, in preparation); they can lead to 10% underestimation of the total masses in our analysis (e.g., Evrard et al. 1996; Rasia et al. 2004; Kay et al. 2004; Faltenbacher et al. 2005).”
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].”
LoCuSS: comparison of observed X-ray and lensing galaxy cluster scaling relations with simulations (2008, background): “Recent simulations (e.g. Rasia et al. 2004, 2006; Nagai et al. 2007a) show that the X-ray total mass Article published by EDP Sciences measured via hydrostatic equilibrium can be biased low by up to 20 per cent for nearby relaxed clusters and therefore the normalization of the mass-temperature…”