Understanding the Equilibrium Structure of CDM Halos

Shapiro, Paul R.; Ahn, Kyungjin; Alvarez, Marcelo A.; Iliev, Ilian T.; Martel, Hugo

doi:10.1051/eas:2006036

Cited by 17 publications

(26 citation statements)

References 134 publications

(271 reference statements)

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“…The difference of TIS with our analysis is that we consider all non-singular solutions of the modified Emden equation (32) and not only the specific TIS one. This model is in a very good agreement with simulations and observations [77], at least outside the inner regions of the cluster. In the inner regions the TIS model predicts a soft core, however collisionless Nbody simulations of dark matter haloes predict a cusp, rather than a core.…”

Section: Galaxy Clusters In the Presence Of Dark Energysupporting

confidence: 87%

Galaxy clusters and structure formation in quintessence versus phantom dark energy universe

et al. 2014

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The self-gravitating gas in the Newtonian limit is studied in the presence of dark energy with a linear and constant equation of state. Entropy extremization associates to the isothermal Boltzmann distribution an effective density that includes 'dark energy particles', which either strengthen or weaken mutual gravitational attraction, in case of quintessence or phantom dark energy, respectively, that satisfy a linear equation of state. Stability is studied for microcanonical (fixed energy) and canonical (fixed temperature) ensembles. Compared to the previously studied cosmological constant case, in the present work it is found that quintessence increases, while phantom dark energy decreases the instability domain under gravitational collapse. Thus, structures are more easily formed in a quintessence rather than in a phantom dominated Universe. Assuming that galaxy clusters are spherical, nearly isothermal and in hydrostatic equilibrium we find that dark energy with a linear and constant equation of state, for fixed radius, mass and temperature, steepens their total density profile! In case of a cosmological constant, this effect accounts for a 1.5% increase in the density contrast, that is the center to edge density ratio of the cluster. We also propose a method to constrain phantom dark energy.

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Section: Galaxy Clusters In the Presence Of Dark Energysupporting

confidence: 87%

Galaxy clusters and structure formation in quintessence versus phantom dark energy universe

et al. 2014

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“…Thus, even for spherical objects the spins k 3 and k 4 will not be identical. In fact, Shapiro et al (2004) pointed out that the presence of infalling matter acts as a surface pressure even for collisionless DM. The surface term leads to 2T þ U > 0.…”

Section: Spinmentioning

confidence: 99%

Shape, Spin, and Baryon Fraction of Clusters in the MareNostrum Universe

Gottlöber

Yepes

2007

ApJ

104

113

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The MareNostrum Universe is one of the largest cosmological smoothed particle hydrodynamics simulations done so far. It consists of 1024 3 dark and 1024 3 gas particles in a box of 500 h À1 Mpc on a side. Here we study the shapes and spins of the dark matter and gas components of the 10,000 most massive objects extracted from the simulation as well as the gas fraction in those objects. We find that the shapes of objects tend to be prolate both in the dark matter and gas. There is a clear dependence of shape on halo mass, the more massive ones being less spherical than the less massive objects. The gas distribution is nevertheless much more spherical than the dark matter, although the triaxiality parameters of gas and dark matter differ only by a few percent, and it increases with cluster mass. The spin parameters of gas and dark matter can be well fitted by a lognormal distribution function. On average, the spin of gas is 1.4 times larger than the spin of dark matter. We find a similar behavior for the spins at higher redshifts, with a slight decrease of the spin ratios to 1.16 at z ¼ 1: The cosmic normalized baryon fraction in the entire cluster sample ranges from Y b ¼ 0:94 at z ¼ 1 to Y b ¼ 0:92 at z ¼ 0. At both redshifts we find a slight, but statistically significant, decrease of Y b with cluster mass.

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“…A good match between their models and the NFW profile requires a fine tuning of initial conditions. Shapiro et al (2004) also explored the importance of CDM accretion history using one-dimensional simulations and very similar arguments to ours. Unfortunately, they use a fluid approach that solves Jeans-like moments of the collisionless Boltzmann equation and, presumably, the elimination of any possible asymmetric velocity distribution prevented them from finding our ρ ∝ r −1 result.…”

Section: Resultsmentioning

confidence: 76%

“…White & Zartisky 1992;Ryden 1993;Sikivie et al 1997;Subramanian et al 2000;Subramanian 2000;Hiotelis 2002;Le Delliou & Henriksen 2003;Shapiro et al 2004;Barnes et al 2005). Applying the collisionless Boltzmann equation to self-similar gravitational collapse, Subramanian (2000) and Subramanian et al (2000) demonstrated that tangential velocities are required to obtain an inner profile that is shallower than that of a singular isothermal sphere.…”

Section: Summary and Discussionmentioning

confidence: 99%

“…Since our model only relies on the mass accretion history and orbit isotropisation to explain the origin of NFW profiles, it naturally explains why collapses with artificially reduced substructure (Moore et al 1999) also lead to the universal profile, even when the initial condition is as smooth as three intersecting plane waves (Shapiro et al 2004). However, if it is so smooth that the orbits are not isotropised then a steeper central slope may result.…”

Section: Summary and Discussionmentioning

confidence: 99%

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The origin of cold dark matter halo density profiles

2006

EAS Publications Series

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N -body simulations predict that CDM halo-assembly occurs in two phases: 1) a fast accretion phase with a rapidly deepening potential well; and 2) a slow accretion phase characterised by a gentle addition of mass to the outer halo with little change in the inner potential well. We demonstrate, using one-dimensional simulations, that this two-phase accretion leads to CDM halos of the NFW form and provides physical insight into the properties of the mass accretion history that influence the final profile. Assuming that the velocities of CDM particles are effectively isotropised by fluctuations in the gravitational potential during the fast accretion phase, we show that gravitational collapse in this phase leads to an inner profile ρ(r) ∝ r −1 . Slow accretion onto an established potential well leads to an outer profile with ρ(r) ∝ r −3 . The concentration of a halo is determined by the fraction of mass that is accreted during the fast accretion phase. Using an ensemble of realistic mass accretion histories, we show that the model predictions of the dependence of halo concentration on halo formation time, and hence the dependence of halo concentration on halo mass, and the distribution of halo concentrations all match those found in cosmological N -body simulations. Using a simple analytic model that captures much of the important physics we show that the inner r −1 profile of CDM halos is a natural result of hierarchical mass assembly with a initial phase of rapid accretion.

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Understanding the Equilibrium Structure of CDM Halos

Cited by 17 publications

References 134 publications

Galaxy clusters and structure formation in quintessence versus phantom dark energy universe

Galaxy clusters and structure formation in quintessence versus phantom dark energy universe

Shape, Spin, and Baryon Fraction of Clusters in the MareNostrum Universe

The origin of cold dark matter halo density profiles

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