127 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
Using the Topology of Large Scale Structure to constrain Dark Energy
The use of standard rulers, such as the scale of the Baryonic Acoustic
oscillations (BAO), has become one of the more powerful techniques employed in
cosmology to probe the entity driving the accelerating expansion of the
Universe. In this paper, the topology of large scale structure (LSS) is used as
one such standard ruler to study this mysterious `dark energy'. By following
the redshift evolution of the clustering of luminous red galaxies (LRGs) as
measured by their 3D topology (counting structures in the cosmic web), we can
chart the expansion rate and extract information about the equation of state of
dark energy. Using the technique first introduced in (Park & Kim, 2009), we
evaluate the constraints that can be achieved using 3D topology measurements
from next-generation LSS surveys such as the Baryonic Oscillation Spectroscopic
Survey (BOSS). In conjunction with the information that will be available from
the Planck satellite, we find a single topology measurement on 3 different
scales is capable of constraining a single dark energy parameter to within 5%
and 10% when dynamics are permitted. This offers an alternative use of the data
available from redshift surveys and serves as a cross-check for BAO studies.Comment: 8 pages, 5 figures, 2 tables, Submitted to MNRAS, updated
acknowledgement
The New Horizon Run Cosmological N-Body Simulations
We present two large cosmological N-body simulations, called Horizon Run 2
(HR2) and Horizon Run 3 (HR3), made using 6000^3 = 216 billions and 7210^3 =
374 billion particles, spanning a volume of (7.200 Gpc/h)^3 and (10.815
Gpc/h)^3, respectively. These simulations improve on our previous Horizon Run 1
(HR1) up to a factor of 4.4 in volume, and range from 2600 to over 8800 times
the volume of the Millennium Run. In addition, they achieve a considerably
finer mass resolution, down to 1.25x10^11 M_sun/h, allowing to resolve
galaxy-size halos with mean particle separations of 1.2 Mpc/h and 1.5 Mpc/h,
respectively. We have measured the power spectrum, correlation function, mass
function and basic halo properties with percent level accuracy, and verified
that they correctly reproduce the LCDM theoretical expectations, in excellent
agreement with linear perturbation theory. Our unprecedentedly large-volume
N-body simulations can be used for a variety of studies in cosmology and
astrophysics, ranging from large-scale structure topology, baryon acoustic
oscillations, dark energy and the characterization of the expansion history of
the Universe, till galaxy formation science - in connection with the new
SDSS-III. To this end, we made a total of 35 all-sky mock surveys along the
past light cone out to z=0.7 (8 from the HR2 and 27 from the HR3), to simulate
the BOSS geometry. The simulations and mock surveys are already publicly
available at http://astro.kias.re.kr/Horizon-Run23/.Comment: 18 pages, 10 figures. Added clarification on Fig 6. Published in the
Journal of the Korean Astronomical Society (JKAS). The paper with
high-resolution figures is available at
http://jkas.kas.org/journals/2011v44n6/v44n6.ht
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