221 research outputs found
Topology of Large-Scale Structure by Galaxy Type: Hydrodynamic Simulations
The topology of large scale structure is studied as a function of galaxy type
using the genus statistic. In hydrodynamical cosmological CDM simulations,
galaxies form on caustic surfaces (Zeldovich pancakes) then slowly drain onto
filaments and clusters. The earliest forming galaxies in the simulations
(defined as ``ellipticals") are thus seen at the present epoch preferentially
in clusters (tending toward a meatball topology), while the latest forming
galaxies (defined as ``spirals") are seen currently in a spongelike topology.
The topology is measured by the genus (= number of ``donut" holes - number of
isolated regions) of the smoothed density-contour surfaces. The measured genus
curve for all galaxies as a function of density obeys approximately the
theoretical curve expected for random-phase initial conditions, but the early
forming elliptical galaxies show a shift toward a meatball topology relative to
the late forming spirals. Simulations using standard biasing schemes fail to
show such an effect. Large observational samples separated by galaxy type could
be used to test for this effect.Comment: Princeton University Observatory, submitted to The Astrophysical
Journal, figures can be ftp'ed from ftp://astro.princeton.edu/cen/TOP
Topology of COBE Microwave Background Fluctuations
We have measured the topology (genus) of the fluctuations in the cosmic
microwave background seen in the recently completed (four-year) data set
produced by the COBE satellite. We find that the genus is consistent with that
expected from a random-phase Gaussian distribution, as might be produced
naturally in inflationary models.Comment: 2 pages, one Post-Script figure, MNRAS LaTeX Style (mn.sty),
submitted to MNRA
Static Einstein-Maxwell Solutions in 2+1 dimensions
We obtain the Einstein-Maxwell equations for (2+1)-dimensional static
space-time, which are invariant under the transformation
. It is shown that the
magnetic solution obtained with the help of the procedure used in
Ref.~\cite{Cataldo}, can be obtained from the static BTZ solution using an
appropriate transformation. Superpositions of a perfect fluid and an electric
or a magnetic field are separately studied and their corresponding solutions
found.Comment: 8 pages, LaTeX, no figures, to appear in Physical Review
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