Clusters of Galaxies: Setting the Stage

Diaferio, Antonaldo; Schindler, S.; Dolag, K.

doi:10.1007/s11214-008-9324-5

Cited by 15 publications

(15 citation statements)

References 152 publications

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“…However, the caustic technique is based on the hypothesis that clusters form by hierarchical clustering; wide observational evidence, based on X-ray and optical data, including gravitational lensing studies (e.g. Diaferio et al 2008;Borgani & Kravtsov 2011), suggest that this hypothesis is well founded. Therefore we expect that N -body simulated clusters are a reasonable representation of real clusters and that the results of our analysis can be safely applied to real clusters.…”

Section: Resultsmentioning

confidence: 99%

Identification of Members in the Central and Outer Regions of Galaxy Clusters

Serra

Diaferio

2013

ApJ

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The caustic technique measures the mass of galaxy clusters in both their virial and infall regions and, as a byproduct, yields the list of cluster galaxy members. Here we use 100 galaxy clusters with mass M 200 ≥ 10 14 h −1 M ⊙ extracted from a cosmological N -body simulation of a ΛCDM universe to test the ability of the caustic technique to identify the cluster galaxy members. We identify the true threedimensional members as the gravitationally bound galaxies. The caustic technique uses the caustic location in the redshift diagram to separate the cluster members from the interlopers. We apply the technique to mock catalogs containing 1000 galaxies in the field of view of 12h −1 Mpc on a side at the cluster location. On average, this sample size roughly corresponds to 180 real galaxy members within 3r 200 , similar to recent redshift surveys of cluster regions. The caustic technique yields a completeness, the fraction of identified true members, f c = 0.95 ± 0.03 within 3r 200 . The contamination, the fraction of interlopers in the observed catalog of members, increases from f i = 0.020 +0.046 −0.015 at r 200 to f i = 0.08 +0.11 −0.05 at 3r 200 . No other technique for the identification of the members of a galaxy cluster provides such large completeness and small contamination at these large radii. The caustic technique assumes spherical symmetry and the asphericity of the cluster is responsible for most of the spread of the completeness and the contamination. By applying the technique to an approximately spherical system obtained by stacking the individual clusters, the spreads decrease by at least a factor of two. We finally estimate the cluster mass within 3r 200 after removing the interlopers: for individual clusters, the mass estimated with the virial theorem is unbiased and within 30% of the actual mass; this spread decreases to less than 10% for the spherically symmetric stacked cluster.

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Section: Resultsmentioning

confidence: 99%

Identification of Members in the Central and Outer Regions of Galaxy Clusters

Serra

Diaferio

2013

ApJ

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“…Clusters of galaxies are valuable tools to measure the cosmological parameters and test structure formation models (e.g. Voit 2005; Diaferio, Schindler & Dolag 2008) and the galaxy–environment connection (e.g. Domínguez, Muriel & Lambas 2001; Martínez, Coenda & Muriel 2008; Huertas‐Company et al 2009; Skibba et al 2009).…”

Section: Introductionmentioning

confidence: 99%

Measuring the escape velocity and mass profiles of galaxy clusters beyond their virial radius

Serra

Diaferio

Murante

et al. 2010

Monthly Notices of the Royal Astronomical Society

127

266

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The caustic technique uses galaxy redshifts alone to measure the escape velocity and mass profiles of galaxy clusters to clustrocentric distances well beyond the virial radius, where dynamical equilibrium does not necessarily hold. We provide a detailed description of this technique and analyse its possible systematic errors. We apply the caustic technique to clusters with mass M200≥ 1014 h−1 M⊙ extracted from a cosmological hydrodynamic simulation of a ΛCDM universe. With a few tens of redshifts per squared comoving megaparsec within the cluster, the caustic technique, on average, recovers the profile of the escape velocity from the cluster with better than 10 per cent accuracy up to r∼ 4r200. The caustic technique also recovers the mass profile with better than 10 per cent accuracy in the range (0.6–4) r200, but it overestimates the mass up to 70 per cent at smaller radii. This overestimate is a consequence of neglecting the radial dependence of the filling function . The 1σ uncertainty on individual escape velocity profiles increases from ∼20 to ∼50 per cent when the radius increases from r∼ 0.1r200 to ∼4r200. Individual mass profiles have 1σ uncertainty between 40 and 80 per cent within the radial range (0.6–4) r200. When the correct virial mass is known, the 1σ uncertainty reduces to a constant 50 per cent on the same radial range. We show that the amplitude of these uncertainties is completely due to the assumption of spherical symmetry, which is difficult to drop. Other potential refinements of the technique are not crucial. We conclude that, when applied to individual clusters, the caustic technique generally provides accurate escape velocity and mass profiles, although, in some cases, the deviation from the real profile can be substantial. Alternatively, we can apply the technique to synthetic clusters obtained by stacking individual clusters: in this case, the 1σ uncertainty on the escape velocity profile is smaller than 20 per cent out to 4r200. The caustic technique thus provides reliable average profiles which extend to regions difficult or impossible to probe with other techniques.

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“…According to the currently favored hierarchical model of cosmic structure formation, larger objects formed through successive mergers of smaller objects with galaxy clusters sitting on top of this mass hierarchy (see Voit 2005 for a review). Most of the mass (∼80%) in a cluster is dark matter (DM), as indicated by galaxy dynamics and gravitational lensing (Diaferio et al 2008). Baryonic gas making up the intracluster medium (ICM) contributes about 15% of the total cluster mass, and individual galaxies account for the remainder (about 5%).…”

Section: Introductionmentioning

confidence: 99%

CONSTRAINTS ON COSMIC RAYS, MAGNETIC FIELDS, AND DARK MATTER FROM GAMMA-RAY OBSERVATIONS OF THE COMA CLUSTER OF GALAXIES WITH VERITAS ANDFERMI

Arlen

Aune

Beilicke

et al. 2012

ApJ

103

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Observations of radio halos and relics in galaxy clusters indicate efficient electron acceleration. Protons should likewise be accelerated and, on account of weak energy losses, can accumulate, suggesting that clusters may also be sources of very high energy (VHE; E > 100 GeV) gamma-ray emission. We report here on VHE gamma-ray observations of the Coma galaxy cluster with the VERITAS array of imaging Cerenkov telescopes, with complementing Fermi Large Area Telescope observations at GeV energies. No significant gamma-ray emission from the Coma Cluster was detected. Integral flux upper limits at the 99% confidence level were measured to be on the order of (2-5) × 10 −8 photons m −2 s −1 (VERITAS, >220 GeV) and ∼2 × 10 −6 photons m −2 s −1 (Fermi, 1-3 GeV), respectively. We use the gamma-ray upper limits to constrain cosmic rays (CRs) and magnetic fields in Coma. Using an analytical approach, the CR-to-thermal pressure ratio is constrained to be <16% from VERITAS data and <1.7% from Fermi data (averaged within the virial radius). These upper limits are starting to constrain the CR physics in self-consistent cosmological cluster simulations and cap the maximum CR acceleration efficiency at structure formation shocks to be <50%. Alternatively, this may argue for non-negligible CR transport processes such as CR streaming and diffusion into the outer cluster regions. Assuming that the radio-emitting electrons of the Coma halo result from hadronic CR interactions, the observations imply a lower limit on the central magnetic field in Coma of ∼(2-5.5) μG, depending on the radial magnetic field profile and on the gamma-ray spectral index. Since these values are below those inferred by Faraday rotation measurements in Coma (for most of the parameter space), this renders the hadronic model a very plausible explanation of the Coma radio halo. are dark matter (DM) dominated, the VERITAS upper limits have been used to place constraints on the thermally averaged product of the total self-annihilation cross section and the relative velocity of the DM particles, σ v .

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Clusters of Galaxies: Setting the Stage

Cited by 15 publications

References 152 publications

Identification of Members in the Central and Outer Regions of Galaxy Clusters

Identification of Members in the Central and Outer Regions of Galaxy Clusters

Measuring the escape velocity and mass profiles of galaxy clusters beyond their virial radius

CONSTRAINTS ON COSMIC RAYS, MAGNETIC FIELDS, AND DARK MATTER FROM GAMMA-RAY OBSERVATIONS OF THE COMA CLUSTER OF GALAXIES WITH VERITAS ANDFERMI

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