5,171 research outputs found
Pointwise convergence of vector-valued Fourier series
We prove a vector-valued version of Carleson's theorem: Let Y=[X,H]_t be a
complex interpolation space between a UMD space X and a Hilbert space H. For
p\in(1,\infty) and f\in L^p(T;Y), the partial sums of the Fourier series of f
converge to f pointwise almost everywhere. Apparently, all known examples of
UMD spaces are of this intermediate form Y=[X,H]_t. In particular, we answer
affirmatively a question of Rubio de Francia on the pointwise convergence of
Fourier series of Schatten class valued functions.Comment: 26 page
Cosmological Implications of the Fundamental Relations of X-ray Clusters
Based on the two-parameter family nature of X-ray clusters of galaxies
obtained in a separate paper, we discuss the formation history of clusters and
cosmological parameters of the universe. Utilizing the spherical collapse model
of cluster formation, and assuming that the cluster X-ray core radius is
proportional to the virial radius at the time of the cluster collapse, the
observed relations among the density, radius, and temperature of clusters imply
that cluster formation occurs in a wide range of redshift. The observed
relations favor the low-density universe. Moreover, we find that the model of
is preferable.Comment: 7 pages, 4 figures. To be published in ApJ Letter
Há alternativas ao uso dos transgênicos?
A existência ou não de alternativa ao uso de transgênicos capaz de satisfazer a demanda mundial por alimento e nutrientes é uma questão que permanece aberta à investigação científica.A importância dos transgênicos ainda não está bem fundamentada no conhecimento científico disponível,em parte porque as conquistas e o potencial da agroecologia não foram objeto de atenção científica suficiente
A Test of the Collisional Dark Matter Hypothesis from Cluster Lensing
Spergel & Steinhardt proposed the possibility that the dark matter particles
are self-interacting, as a solution to two discrepancies between the
predictions of cold dark matter models and the observations: first, the
observed dark matter distribution in some dwarf galaxies has large,
constant-density cores, as opposed to the predicted central cusps; and second,
small satellites of normal galaxies are much less abundant than predicted. The
dark matter self-interaction would produce isothermal cores in halos, and would
also expel the dark matter particles from dwarfs orbiting within large halos.
However, another inevitable consequence of the model is that halos should
become spherical once most particles have interacted. Here, I rule out this
model by the fact that the innermost regions of dark matter halos in massive
clusters of galaxies are elliptical, as shown by gravitational lensing and
other observations. The absence of collisions in the lensing cores of massive
clusters implies that any dark matter self-interaction is too weak to have
affected the observed density profiles in the dark-matter dominated dwarf
galaxies, or to have eased the destruction of dwarf satellites in galactic
halos. If is the cross section and the mass of the dark matter
particle, then s_x/m_x < 10^{-25.5} \cm^2/\gev.Comment: to appear in ApJ, January 1 200
Characterizing the Cluster Lens Population
We present a detailed investigation into which properties of CDM halos make
them effective strong gravitational lenses. Strong lensing cross sections of
878 clusters from an N-body simulation are measured by ray tracing through
13,594 unique projections. We measure concentrations, axis ratios,
orientations, and the amount of substructure of each cluster, and compare the
lensing weighted distribution of each quantity to that of the cluster
population as a whole. The concentrations of lensing clusters are on average
34% larger than the typical cluster in the Universe. Despite this bias, the
anomalously high concentrations (c >14) recently measured by several groups,
appear to be inconsistent with the concentration distribution in our
simulations, which predict < 2% of lensing clusters should have concentrations
this high. No correlation is found between lensing cross section and the amount
of substructure. We introduce several types of simplified dark matter halos,
and use them to isolate which properties of CDM clusters make them effective
lenses. Projections of halo substructure onto small radii and the large scale
mass distribution of clusters do not significantly influence cross sections.
The abundance of giant arcs is primarily determined by the mass distribution
within an average overdensity of ~ 10,000. A multiple lens plane ray tracing
algorithm is used to show that projections of large scale structure increase
the giant arc abundance by a modest amount <7%. We revisit the question of
whether there is an excess of giant arcs behind high redshift clusters in the
RCS survey and find that the number of high redshift (z > 0.6) lenses is in
good agreement with LCDM, although our simulations predict more low redshift (z
< 0.6) lenses than were observed. (abridged)Comment: 19 pages, 15 figures. Submitted to Ap
The Variation of Gas Mass Distribution in Galaxy Clusters: Effects of Preheating and Shocks
We investigate the origin of the variation of the gas mass fraction in the
core of galaxy clusters, which was indicated by our work on the X-ray
fundamental plane. The adopted model supposes that the gas distribution
characterized by the slope parameter is related to the preheated temperature.
Comparison with observations of relatively hot (~> 3 keV) and low redshift
clusters suggests that the preheated temperature is about 0.5-2 keV, which is
higher than expected from the conventional galactic wind model and possibly
suggests the need for additional heating such as quasars or gravitational
heating on the largest scales at high redshift. The dispersion of the preheated
temperature may be attributed to the gravitational heating in subclusters. We
calculate the central gas fraction of a cluster from the gas distribution,
assuming that the global gas mass fraction is constant within a virial radius
at the time of the cluster collapse. We find that the central gas density thus
calculated is in good agreement with the observed one, which suggests that the
variation of gas mass fraction in cluster cores appears to be explained by
breaking the self-similarity in clusters due to preheated gas. We also find
that this model does not change major conclusions on the fundamental plane and
its cosmological implications obtained in previous papers, which strongly
suggests that not only for the dark halo but also for the intracluster gas the
core structure preserves information about the cluster formation.Comment: 17 pages, to be published in Ap
Constraints on Cosmological Parameters from Future Galaxy Cluster Surveys
We study the expected redshift evolution of galaxy cluster abundance between
0 < z < 3 in different cosmologies, including the effects of the cosmic
equation of state parameter w=p/rho. Using the halo mass function obtained in
recent large scale numerical simulations, we model the expected cluster yields
in a 12 deg^2 Sunyaev-Zeldovich Effect (SZE) survey and a deep 10^4 deg^2 X-ray
survey over a wide range of cosmological parameters. We quantify the
statistical differences among cosmologies using both the total number and
redshift distribution of clusters. Provided that the local cluster abundance is
known to a few percent accuracy, we find only mild degeneracies between w and
either Omega_m or h. As a result, both surveys will provide improved
constraints on Omega_m and w. The Omega_m-w degeneracy from both surveys is
complementary to those found either in studies of CMB anisotropies or of
high-redshift Supernovae (SNe). As a result, combining these surveys together
with either CMB or SNe studies can reduce the statistical uncertainty on both w
and Omega_m to levels below what could be obtained by combining only the latter
two data sets. Our results indicate a formal statistical uncertainty of about
3% (68% confidence) on both Omega_m and w when the SZE survey is combined with
either the CMB or SN data; the large number of clusters in the X-ray survey
further suppresses the degeneracy between w and both Omega_m and h. Systematics
and internal evolution of cluster structure at the present pose uncertainties
above these levels. We briefly discuss and quantify the relevant systematic
errors. By focusing on clusters with measured temperatures in the X-ray survey,
we reduce our sensitivity to systematics such as non-standard evolution of
internal cluster structure.Comment: ApJ, revised version. Expanded discussion of systematics;
Press-Schechter mass function replaced by fit from simulation
Non-linear power spectra of dark and luminous matter in halo model of structure formation
The late stages of large-scale structure evolution are treated
semi-analytically within the framework of modified halo model. We suggest
simple yet accurate approximation for relating the non-linear amplitude to
linear one for spherical density perturbation. For halo concentration
parameter, , a new computation technique is proposed, which eliminates the
need of interim evaluation of the . Validity of the technique is
proved for CDM and WDM cosmologies. Also, the parameters for
Sheth-Tormen mass function are estimated. The modified and extended halo model
is applied for determination of non-linear power spectrum of dark matter, as
well as for galaxy power spectrum estimation. The semi-analytical techniques
for dark matter power spectrum are verified by comparison with data from
numerical simulations. Also, the predictions for the galaxy power spectra are
confronted with 'observed' data from PSCz and SDSS galaxy catalogs, good
accordance is found.Comment: 18 pages, 8 figures; major changes from the previous version;
accepted for publivation in Phys. Rev.
Spectroscopic Observations of Optically Selected Clusters of Galaxies from the Palomar Distant Cluster Survey
We have conducted a redshift survey of sixteen cluster candidates from the
Palomar Distant Cluster Survey (PDCS) to determine both the density of PDCS
clusters and the accuracy of the estimated redshifts presented in the PDCS
catalog (Postman et. al. 1996). We find that the matched-filter redshift
estimate presented in the PDCS has an error sigma_z = 0.06 in the redshift
range 0.1 < z < 0.35 based on eight cluster candidates with three or more
concordant galaxy redshifts.
We measure the low redshift (0.1 < z < 0.35) space density of PDCS clusters
to be 31.3^{+30.5}_{-17.1} * E-06 h^3 Mpc^-3 (68% confidence limits for a
Poisson distribution) for Richness Class 1 systems. We find a tentative space
density of 10.4^{+23.4}_{-8.4}* E-06 h^3 Mpc^-3 for Richness Class 2 clusters.
These densities compare favorably with those found for the whole of the PDCS
and support the finding that the space density of clusters in the PDCS is a
factor of ~5 above that of clusters in the Abell catalog (Abell 1958; Abell,
Corwin, and Olowin 1989). These new space density measurements were derived as
independently as possible from the original PDCS analysis and therefore,
demonstrate the robustness of the original work. Based on our survey, we
conclude that the PDCS matched-filter algorithm is successful in detecting real
clusters and in estimating their true redshifts in the redshift range we
surveyed.Comment: 23 pages with 4 figures and 3 seperate tables. To be published in the
November Issue of the Astronomical Journa
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