9,281 research outputs found
The scale of homogeneity in the Las Campanas Redshift Survey
We analyse the Las Campanas Redshift Survey using the integrated conditional
density (or density of neighbors) in volume-limited subsamples up to
unprecedented scales (200 Mpc/) in order to determine without ambiguity the
behavior of the density field. We find that the survey is well described by a
fractal up to 20-30 Mpc/, but flattens toward homogeneity at larger scales.
Although the data are still insufficient to establish with high significance
the expected homogeneous behavior, and therefore to rule out a fractal trend to
larger scales, a fit with a CDM-like spectrum with high normalization well
represents the data.Comment: 8 pages, 3 figures, accepted on Ap.J. Letter
Reconstructing the linear power spectrum of cosmological mass fluctuations
We describe an attempt to reconstruct the initial conditions for the
formation of cosmological large-scale structure. The power spectrum of the
primordial fluctuations is affected by bias, nonlinear evolution and
redshift-space distortions, but we show how these effects can be corrected for
analytically. Using eight independent datasets, we obtain excellent agreement
in the estimated linear power spectra given the following conditions. First,
the relative bias factors for Abell clusters, radio galaxies, optical galaxies
and IRAS galaxies must be in the ratios 4.5:1.9:1.3:1. Second, the data require
redshift-space distortion: \Omega^{0.6}/b_{\ss I}
= 1.0 \pm 0.2. Third, low values of and bias are disfavoured. The
shape of the spectrum is extremely well described by a CDM transfer function
with an apparent value of the fitting parameter . Tilted models
predict too little power at 100 Mpc wavelengths.Comment: Edinburgh Astronomy Preprint 26/93. Accepted for publication in
Monthly Notices of the RAS. 13 pages of LaTeX, plus 10 PostScript figures.
You will need the mn.sty style file (from babbage: get mn.sty). The figure
.ps files are in the usual self-unpacking unix scrip
Formalism for the Subhalo Mass Function in the Tidal-limit Approximation
We present a theoretical formalism by which the global and the local mass
functions of dark matter substructures (dark subhalos) can be analytically
estimated. The global subhalo mass function is defined to give the total number
density of dark subhalos in the universe as a function of mass, while the local
subhalo mass function counts only those subhalos included in one individual
host halo. We develop our formalism by modifying the Press-Schechter theory to
incorporate the followings: (i) the internal structure of dark halos; (ii) the
correlations between the halos and the subhalos; (iii) the subhalo mass-loss
effect driven by the tidal forces. We find that the resulting (cumulative)
subhalo mass function is close to a power law with the slope of ~ -1, that the
subhalos contribute approximately 10 % of the total mass, and that the tidal
stripping effect changes the subhalo mass function self-similarly, all
consistent with recent numerical detections.Comment: revised version, accepted by ApJ Letters, estimate of the local
subhalo mass function included, 10 pages, 1 figur
Nonlinear Gravitational Clustering: dreams of a paradigm
We discuss the late time evolution of the gravitational clustering in an
expanding universe, based on the nonlinear scaling relations (NSR) which
connect the nonlinear and linear two point correlation functions. The existence
of critical indices for the NSR suggests that the evolution may proceed towards
a universal profile which does not change its shape at late times. We begin by
clarifying the relation between the density profiles of the individual halo and
the slope of the correlation function and discuss the conditions under which
the slopes of the correlation function at the extreme nonlinear end can be
independent of the initial power spectrum. If the evolution should lead to a
profile which preserves the shape at late times, then the correlation function
should grow as [in a universe] een at nonlinear scales. We
prove that such exact solutions do not exist; however, ther e exists a class of
solutions (``psuedo-linear profiles'', PLP's for short) which evolve as
to a good approximation. It turns out that the PLP's are the correlation
functions which arise if the individual halos are assumed to be isothermal
spheres. They are also configurations of mass in which the nonlinear effects of
gravitational clustering is a minimum and hence can act as building blocks of
the nonlinear universe. We discuss the implicatios of this result.Comment: 32 Pages, Submitted to Ap
Measuring the galaxy power spectrum with multiresolution decomposition -- II. diagonal and off-diagonal power spectra of the LCRS galaxies
The power spectrum estimator based on the discrete wavelet transform (DWT)
for 3-dimensional samples has been studied. The DWT estimator for
multi-dimensional samples provides two types of spectra with respect to
diagonal and off-diagonal modes, which are very flexible to deal with
configuration-related problems in the power spectrum detection. With simulation
samples and mock catalogues of the Las Campanas redshift survey (LCRS), we show
(1) the slice-like geometry of the LCRS doesn't affect the off-diagonal power
spectrum with ``slice-like'' mode; (2) the Poisson sampling with the LCRS
selection function doesn't cause more than 1- error in the DWT power
spectrum; and (3) the powers of peculiar velocity fluctuations, which cause the
redshift distortion, are approximately scale-independent. These results insure
that the uncertainties of the power spectrum measurement are under control. The
scatter of the DWT power spectra of the six strips of the LCRS survey is found
to be rather small. It is less than 1- of the cosmic variance of mock
samples in the wavenumber range h Mpc. To fit the detected
LCRS diagonal DWT power spectrum with CDM models, we find that the best-fitting
redshift distortion parameter is about the same as that obtained from
the Fourier power spectrum. The velocity dispersions for SCDM and
CDM models are also consistent with other detections with
the LCRS. A systematic difference between the best-fitting parameters of
diagonal and off-diagonal power spectra has been significantly measured. This
indicates that the off-diagonal power spectra are capable of providing
information about the power spectrum of galaxy velocity field.Comment: AAS LaTeX file, 41 pages, 10 figures included, accepted for
publication in Ap
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