8 research outputs found
Decaying Neutrinos in Galaxy Clusters
Davidsen et al. (1991) have argued that the failure to detect uv photons from
the dark matter DM) in cluster A665 excludes the decaying neutrino hypothesis.
Sciama et al. (1993) argued that because of high central concentration the DM
in that cluster must be baryonic. We study the DM profile in clusters of
galaxies simulated using the Harrison--Zel'dovich spectrum of density
fluctuations, and an amplitude previously derived from numerical simulations
(Melott 1984b; Anninos et al. 1991) and in agreement with microwave background
fluctuations (Smoot et al. 1992). We find that with this amplitude
normalization cluster neutrino DM densities are comparable to observed cluster
DM values. We conclude that given this normalization, the cluster DM should be
at least largely composed of neutrinos. The constraint of Davidsen et al. can
be somewhat weakened by the presence of baryonic DM; but it cannot be
eliminated given our assumptions.Comment: 14 pages, requires aaspp.sty. All latex, style files, and postscript
files included in a uuencoded compressed-tar file.
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Demonstrating Discreteness and Collision Error in Cosmological N-body Simulations of Dark Matter Gravitational Clustering
Two-body scattering and other discreteness effects are unimportant in
cosmological gravitational clustering in most scenarios, since the dark matter
has a small particle mass. The collective field should determine evolution:
Two-body scattering in simulations violates the Poisson-Vlasov equations. We
test this in PM, PM, Tree, and NGPM codes, noting that a collisionless code
will preserve the one-dimensional character of plane wave collapse. We find
collisionality vanishing as the softening parameter approaches the mean
interparticle separation. Solutions for the problem are suggested, involving
greater computer power, PM-based nested grid codes, and a more conservative
approach to resolution claims.Comment: Final version accepted for ApJ Letters. Minor revisions, including
due to bug fix in tree code. Uses aasms4.sty. 15 pages. Higher resolution
figures available at ftp://kusmos.phsx.ukans.edu/preprints/discret
The Ellipticity and Orientation of Clusters of Galaxies from N-Body Experiments
In this study we use simulations of 128 particles to study the
ellipticity and orientation of clusters of galaxies in N-body simulations of
differing power-law initial spectra (P(k) \propto k^n ,n = +1, 0, -1, -2\Omega_0 = 0.2nD < 15 h^{-1}n-$dependent way.Comment: 22 pages, requires aaspp4.sty, flushrt.sty, and epsf.sty Revised
manuscript, accepted for publication in Ap
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