36,462 research outputs found
The Santa Fe Light Cone Simulation Project: II. The Prospects for Direct Detection of the WHIM with SZE Surveys
Detection of the Warm-Hot Intergalactic Medium (WHIM) using Sunyaev-Zeldovich
effect (SZE) surveys is an intriguing possibility, and one that may allow
observers to quantify the amount of "missing baryons" in the WHIM phase. We
estimate the necessary sensitivity for detecting low density WHIM gas with the
South Pole Telescope (SPT) and Planck Surveyor for a synthetic 100 square
degree sky survey. This survey is generated from a very large, high dynamic
range adaptive mesh refinement cosmological simulation performed with the Enzo
code. We find that for a modest increase in the SPT survey sensitivity (a
factor of 2-4), the WHIM gas makes a detectable contribution to the integrated
sky signal. For a Planck-like satellite, similar detections are possible with a
more significant increase in sensitivity (a factor of 8-10). We point out that
for the WHIM gas, the kinematic SZE signal can sometimes dominate the thermal
SZE where the thermal SZE decrement is maximal (150 GHz), and that using the
combination of the two increases the chance of WHIM detection using SZE
surveys. However, we find no evidence of unique features in the thermal SZE
angular power spectrum that may aid in its detection. Interestingly, there are
differences in the power spectrum of the kinematic SZE, which may not allow us
to detect the WHIM directly, but could be an important contaminant in
cosmological analyses of the kSZE-derived velocity field. Corrections derived
from numerical simulations may be necessary to account for this contamination.Comment: 9 pages, submitted to Astrophysical Journa
Euclidean distance geometry and applications
Euclidean distance geometry is the study of Euclidean geometry based on the
concept of distance. This is useful in several applications where the input
data consists of an incomplete set of distances, and the output is a set of
points in Euclidean space that realizes the given distances. We survey some of
the theory of Euclidean distance geometry and some of the most important
applications: molecular conformation, localization of sensor networks and
statics.Comment: 64 pages, 21 figure
Morphology of Mock SDSS Catalogues
We measure the geometry, topology and morphology of the superclusters in mock
SDSS catalogues prepared by Cole et al.(1998). The mock catalogues refer to
CDM and \LCDM {\em flat} cosmological models and are populated by
galaxies so that these act as biased tracers of mass, conforming with the
correlation function measured using APM catalogue. We compute the Minkowski
Functionals (MFs) for the cosmic density fields using SURFGEN (Sheth et
al.2003) and use the available 10 realizations of CDM to study the effect
of cosmic variance in estimation of MFs and Shapefinders, which we find to be
extremely well constrained statistics. Although all the mock catalogues of
galaxies have the same two-point correlation function and similar clustering
amplitude, the global MFs due to CDM show systematically lower amplitude
compared to those due to \LCDM; an indirect, but detectable effect due to
nonzero, higher order correlation functions. The characteristic thickness (T),
breadth (B) and length (L) of the superclusters are measured using the
available 10 realizations of CDM. While TB and T, B[1,17]
hMpc, we find the top 10 superclusters to be as long as 90 hMpc,
with the longest superclusters identified at percolation to be rare objects
with their length as large as 150 hMpc. The CDM superclusters are
found to be significantly longer than those in \LCDM. Thickness (T), breadth
(B), planarity (P) and mass/volumeweighted planarity and filamentarity of
the superclusters are found to be useful to compare the two models (abridged).Comment: 23 Pages, 12 Figures, MNRAS Style. Minor modifications to the text.
New references adde
Using the filaments in the LCRS to test the LambdaCDM model
It has recently been established that the filaments seen in the Las Campanas
Redshift Survey (LCRS) are statistically significant at scales as large as 70
to 80 Mpc/h in the slice, and 50 to 70 Mpc/h in the five other
LCRS slices. The ability to produce such filamentary features is an important
test of any model for structure formation. We have tested the LCDM model with a
featureless, scale invariant primordial power spectrum by quantitatively
comparing the filamentarity in simulated LCRS slices with the actual data. The
filamentarity in an unbiased LCDM model, we find, is less than the LCRS.
Introducing a bias b=1.15, the model is in rough consistency with the data,
though in two of the slices the filamentarity falls below the data at a low
level of statistical significance. The filamentarity is very sensitive to the
bias parameter and a high value b=1.5, which enhances filamentarity at small
scales and suppresses it at large scales, is ruled out. A bump in the power
spectrum at k~0.05 Mpc/h is found to have no noticeable effect on the
filamentarity.Comment: 16 pages, 3 figures; Minor Changes, Accepted to Ap
Precision of Hubble constant derived using black hole binary absolute distances and statistical redshift information
Measured gravitational waveforms from black hole binary inspiral events
directly determine absolute luminosity distances. To use these data for
cosmology, it is necessary to independently obtain redshifts for the events,
which may be difficult for those without electromagnetic counterparts. Here it
is demonstrated that certainly in principle, and possibly in practice,
clustering of galaxies allows extraction of the redshift information from a
sample statistically for the purpose of estimating mean cosmological
parameters, without identification of host galaxies for individual events. We
extract mock galaxy samples from the 6th Data Release of the Sloan Digital Sky
Survey resembling those that would be associated with inspiral events of
stellar mass black holes falling into massive black holes at redshift z ~ 0.1
to 0.5. A simple statistical procedure is described to estimate a likelihood
function for the Hubble constant H_0: each galaxy in a LISA error volume
contributes linearly to the log likelihood for the source redshift, and the log
likelihood for each source contributes linearly to that of H_0. This procedure
is shown to provide an accurate and unbiased estimator of H_0. It is estimated
that a precision better than one percent in H_0 may be possible if the rate of
such events is sufficiently high, on the order of 20 to z = 0.5.Comment: 9 pages, 4 figures, submitted to Phys. Rev. D; new references adde
Passive discrete-time systems with a Pontryagin state space
Passive discrete-time systems with Hilbert spaces as an incoming and outgoing
space and a Pontryagin space as a state space are investigated. A geometric
characterization when the index of the transfer function coincides with the
negative index of the state space is given. In this case, an isometric
(co-isometric) system has a product representation corresponding to the left
(right) Krein-Langer factorization of the transfer function. A new criterion,
based on the inclusion of reproducing kernel spaces, when a product of two
isometric (co-isometric) systems preserves controllability (observability), is
obtained. The concept of the defect function is expanded for generalized Schur
functions, and realizations of generalized Schur functions with zero defect
functions are studied
- …