74 research outputs found
Evolution of superclusters and supercluster cocoons in various cosmologies
We investigate the evolution of superclusters and supercluster cocoons
(basins of attraction), and the influence of cosmological parameters to the
evolution. We perform numerical simulations of the evolution of the cosmic web
for different cosmological models: the LCDM model with a conventional value of
the dark energy (DE) density, the open model OCDM with no DE, the standard SCDM
model with no DE, and the Hyper-DE HCDM model with an enhanced DE density
value. We find ensembles of superclusters of these models for five evolutionary
stages, corresponding to the present epoch z = 0, and to redshifts z = 1, 3,
10, 30. We use diameters of the largest superclusters and the number of
superclusters as percolation functions to describe properties of the ensemble
of superclusters in the cosmic web. We analyse the size and mass distribution
of superclusters in models and in real Sloan Digital Sky Survey (SDSS) based
samples. In all models numbers and volumes of supercluster cocoons are
independent on cosmological epochs. Supercluster masses increase with time, and
geometrical sizes in comoving coordinates decrease with time, for all models.
LCDM, OCDM and HCDM models have almost similar percolation parameters. This
suggests that the essential parameter, which defines the evolution of
superclusters, is the matter density. The DE density influences the growth of
the amplitude of density perturbations, and the growth of masses of
superclusters, albeit significantly less strongly. The HCDM model has the
largest speed of the growth of the amplitude of density fluctuations, and the
largest growth of supercluster masses during the evolution. Geometrical
diameters and numbers of HCDM superclusters at high threshold densities are
larger than for LCDM and OCDM superclusters. SCDM model has about two times
more superclusters than other models; SCDM superclusters have smaller diameters
and masses.Comment: 14 pages, 10 figures (accepted by Astronomy & Astrophysics). arXiv
admin note: text overlap with arXiv:1901.0937
Correlation function: biasing and fractal properties of the cosmic web
We calculated spatial correlation functions of galaxies, , structure
functions, , gradient functions, , and fractal dimension functions, , using dark
matter particles of the biased cold dark matter (CDM) simulation,
observed galaxies of the Sloan Digital Sky Survey (SDSS), and simulated
galaxies of the Millennium and EAGLE simulations. We analysed how these
functions describe fractal and biasing properties of the cosmic web. The
correlation functions of the biased CDM model samples at small
distances (particle and galaxy separations), ~\Mpc, describe the
distribution of matter inside dark matter (DM) halos. In real and simulated
galaxy samples, only the brightest galaxies in clusters are visible, and the
transition from clusters to filaments occurs at a distance ~\Mpc. Real and simulated galaxies of low luminosity, , have
almost identical correlation lengths and amplitudes, indicating that dwarf
galaxies are satellites of brighter galaxies, and do not form a smooth
population in voids. The combination of several physical processes (e.g. the
formation of halos along the caustics of particle trajectories and the phase
synchronisation of density perturbations on various scales) transforms the
initial random density field to the current highly non-random density field.
Galaxy formation is suppressed in voids, which increases the amplitudes of
correlation functions and power spectra of galaxies, and increases the
large-scale bias parameter. The combined evidence leads to the large-scale bias
parameter of galaxies the value . We find
for the correlation length of
galaxies.Comment: 15 pages, 10 figures, 5 tables. The revised version is accepted by
Astronomy & Astrophysic
Wavelet analysis of the formation of the cosmic web
According to the modern cosmological paradigm galaxies and galaxy systems
form from tiny density perturbations generated during the very early phase of
the evolution of the Universe. Using numerical simulations we study the
evolution of phases of density perturbations of different scales to understand
the formation and evolution of the cosmic web. We apply the wavelet analysis to
follow the evolution of high-density regions (clusters and superclusters) of
the cosmic web. We show that the positions of maxima and minima of density
waves (their spatial phases) almost do not change during the evolution of the
structure. Positions of extrema of density perturbations are the more stable,
the larger is the wavelength of perturbations. Combining observational and
simulation data we conclude that the skeleton of the cosmic web was present
already in an early stage of structure evolution.Comment: 12 pages, 8 figures, revised versio
Probing large-scale structure with large samples of X-ray selected AGN: I. Baryonic acoustic oscillations
© ESO, 2014. We investigate the potential of large X-ray-selected AGN samples for detecting baryonic acoustic oscillations (BAO). Though AGN selection in X-ray band is very clean and efficient, it does not provide redshift information, and thus needs to be complemented with an optical follow-up. The main focus of this study is (i) to find the requirements needed for the quality of the optical follow-up and (ii) to formulate the optimal strategy of the X-ray survey, in order to detect the BAO. We demonstrate that redshift accuracy of σ0 = 10-2 at z = 1 and the catastrophic failure rate of ffail ? 30% are sufficient for a reliable detection of BAO in future X-ray surveys. Spectroscopic quality redshifts (σ0 = 10-3 and ffail ∼ 0) will boost the confidence level of the BAO detection by a factor of ∼2. For meaningful detection of BAO, X-ray surveys of moderate depth of Flim ∼ few 10-15 erg? s-1/cm2 covering sky area from a few hundred to ∼ten thousand square degrees are required. The optimal strategy for the BAO detection does not necessarily require full sky coverage. For example, in a 1000 day-long survey by an eROSITA type telescope, an optimal strategy would be to survey a sky area of ∼9000 deg2, yielding a ∼16σ BAO detection. A similar detection will be achieved by ATHENA+ or WFXT class telescopes in a survey with a duration of 100 days, covering a similar sky area. XMM-Newton can achieve a marginal BAO detection in a 100-day survey covering ∼400 deg2. These surveys would demand a moderate-to-high cost in terms the optical follow-ups, requiring determination of redshifts of ∼105 (XMM-Newton) to ∼3 × 106 objects (eROSITA, ATHENA+, and WFXT) in these sky areas
Power spectrum of the SDSS luminous red galaxies: constraints on cosmological parameters
In this paper we determine the constraints on cosmological parameters using
the CMB data from the WMAP experiment together with the recent power spectrum
measurement of the SDSS Luminous Red Galaxies (LRGs). Specifically, we focus on
spatially flat, low matter density models with adiabatic Gaussian initial
conditions. The spatial flatness is achieved with an additional quintessence
component whose equation of state parameter w_eff is taken to be independent of
redshift. Throughout most of the paper we do not allow any massive neutrino
contribution and also the influence of the gravitational waves on the CMB is
taken to be negligible. The analysis is carried out separately for two cases:
(i) using the acoustic scale measurements as presented in H\"utsi (2006), (ii)
using the full SDSS LRG power spectrum and its covariance matrix. We are able
to obtain a very tight constraint on the Hubble constant: H_0 = 70.8
^{+2.1}_{-2.0} km/s/Mpc, which helps in breaking several degeneracies between
the parameters and allows us to determine the low redshift expansion law with
much higher accuracy than available from the WMAP + HST data alone. The
positive deceleration parameter q_0 is found to be ruled out at 5.5 \sigma
confidence level. Finally, we extend our analysis by investigating the effects
of relaxing the assumption of spatial flatness and also allow for a
contribution from massive neutrinos.Comment: Final version accepted in A&A, added analysis for the models with
massive neutrinos and non-flat spatial geometrie
Origins of the Isospin Violation of Dark Matter Interactions
Light dark matter (DM) with a large DM-nucleon spin-independent cross section
and furthermore proper isospin violation (ISV) may provide
a way to understand the confusing DM direct detection results. Combing with the
stringent astrophysical and collider constraints, we systematically investigate
the origin of ISV first via general operator analyses and further via
specifying three kinds of (single) mediators: A light from chiral
, an approximate spectator Higgs doublet (It can explain the
anomaly simultaneously) and color triplets. In addition, although from an
exotic mixing with generating , we can combine it with
the conventional Higgs to achieve proper ISV. As a concrete example, we propose
the model where the charged light sneutrino is the inelastic
DM, which dominantly annihilates to light dark states such as with sub-GeV
mass. This model can address the recent GoGeNT annual modulation consistent
with other DM direct detection results and free of exclusions.Comment: References added and English greatly improve
Clusters of galaxies in the microwave band: influence of the motion of the Solar System
In this work we consider the changes of the SZ cluster brightness, flux and
number counts induced by the motion of the Solar System with respect to the
frame defined by the cosmic microwave background (CMB). These changes are
connected with the Doppler effect and aberration and exhibit a strong spectral
and spatial dependence. The correction to the SZ cluster brightness and flux
has an amplitude and spectral dependence, which is similar to the first order
cluster peculiar velocity correction to the thermal SZ effect. Due to the
change in the received cluster CMB flux the motion of the Solar System induces
a dipolar asymmetry in the observed number of clusters above a given flux
level. Similar effects were discussed for -ray bursts and radio
galaxies, but here, due to the very peculiar frequency-dependence of the
thermal SZ effect, the number of observed clusters in one direction of the sky
can be both, decreased or increased depending on the frequency band. A
detection of this asymmetry should be possible using future full sky CMB
experiments with mJy sensitivities.Comment: 7 pages, 6 figures, submitted to Astronomy and Astrophysics,
corrected pdf-proble
Constraints on leptonically annihilating Dark Matter from reionization and extragalactic gamma background
The PAMELA, Fermi and HESS experiments (PFH) have shown anomalous excesses in
the cosmic positron and electron fluxes. A very exciting possibility is that
those excesses are due to annihilating dark matter (DM). In this paper we
calculate constraints on leptonically annihilating DM using observational data
on diffuse extragalactic gamma-ray background and measurements of the optical
depth to the last-scattering surface, and compare those with the PFH favored
region in the m_{DM} - plane. Having specified the detailed form
of the energy input with PYTHIA Monte Carlo tools we solve the radiative
transfer equation which allows us to determine the amount of energy being
absorbed by the cosmic medium and also the amount left over for the diffuse
gamma background. We find that the constraints from the optical depth
measurements are able to rule out the PFH favored region fully for the
\tau^{-}+\tau^{+} annihilation channel and almost fully for the \mu^{-}+\mu^{+}
annihilation channel. It turns out that those constraints are quite robust with
almost no dependence on low redshift clustering boost. The constraints from the
gamma-ray background are sensitive to the assumed halo concentration model and,
for the power law model, rule out the PFH favored region for all leptonic
annihilation channels. We also find that it is possible to have models that
fully ionize the Universe at low redshifts. However, those models produce too
large free electron fractions at z > ~100 and are in conflict with the optical
depth measurements. Also, the magnitude of the annihilation cross-section in
those cases is larger than suggested by the PFH data.Comment: A&A accepted, minor changes/additions, added reference
CDM models with a steplike initial power spectrum
We investigate the properties of clusters of galaxies in the CDM
models with a steplike initial power spectrum. We examine the mass function,
the peculiar velocities and the power spectrum of clusters in models with
different values of the density parameter , the normalized Hubble
constant h and the spectral parameter p, which describes the shape of the
initial power spectrum. The results are compared with observations. We also
investigate the rms bulk velocity in the models, where the properties of
clusters are consistent with the observed data. We find that the power spectrum
of clusters is in good agreement with the observed power spectrum of the
Abell-ACO clusters, if the spectral parameter p is in the range p=0.6-0.8. The
power spectrum and the rms peculiar velocity of clusters are consistent with
observations only if . The models are consistent
with the observed properties of clusters, if h=0.50-0.63. For h=0.65, we find
that .Comment: 8 pages, 5 figures. Accepted for publication in MNRA
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