1,398 research outputs found
Clustering of dark matter halos on the light-cone: scale-, time- and mass-dependence of the halo biasing in the Hubble volume simulations
We develop a phenomenological model to predict the clustering of dark matter
halos on the light-cone by combining several existing theoretical models.
Assuming that the velocity field of halos on large scales is approximated by
linear theory, we propose an empirical prescription of a scale-, mass-, and
time-dependence of halo biasing. We test our model against the Hubble Volume
-body simulation and examine its validity and limitations. We find a good
agreement in two-point correlation functions of dark matter halos between the
phenomenological model predictions and measurements from the simulation for
Mpc both in the real and redshift spaces. Although calibrated on the
mass scale of groups and clusters and for redshifts up to , the model
is quite general and can be applied to a wider range of astrophysical objects,
such as galaxies and quasars, if the relation between dark halos and visible
objects is specified.Comment: 5 pages, 2 figures, ApJL accepted. New references adde
The Obama Effect In The Arab World
This paper tests the Obama Effect hypothesis with respect to the Arab world. The paper first presents popular uses of the term and then discusses the thin scholarly literature on the topic. For quantitative data, the paper uses longitudinal data from the Annual Arab Public Opinion Poll from 2004 to 2011, with supplemental data from the Pew Research Center. Furthermore, the paper analyzed data on the Arab Spring in the context of a possible Obama Effect and policy implications for the future of U.S. foreign policy. The paper found insufficient support for the hypothesis due to a lack of theoretical foundation or statistical support in the Arab world. It should be noted that this study was limited due to the lack of survey questions tailored to test this specific hypothesis. Lastly, the paper made suggestions for future U.S. foreign policy in the Arab world as well as for future research
Quantitative studies for photoabsorption and fluorescence of HCl
Photoabsorption and fluorescence cross sections of HCl are investigated in the wavelength region between 105 to 220 nm. The oscillator strengths of discrete structures at wavelengths shorter than 130 nm are measured
Power Spectrum Analysis of the 2dF QSO Sample Revisited
We revisit the power spectrum analysis of the complete sample of the two
degree field (2dF) QSO redshift (2QZ) survey, as a complementary test of the
work by Outram et al. (2003). A power spectrum consistent with that of the 2QZ
group is obtained. Differently from their approach, fitting of the power
spectrum is investigated incorporating the nonlinear effects, the geometric
distortion and the light-cone effect. It is shown that the QSO power spectrum
is consistent with the cold dark matter (CDM) model with the matter
density parameter . Our constraint on the density
parameter is rather weaker than that of the 2QZ group. We also show that the
constraint slightly depends on the equation of state parameter of the dark
energy. The constraint on from the QSO power spectrum is demonstrated,
though it is not very tight.Comment: 15 pages, 5 figures, accepted for publication in the Astrophysical
Journa
Reconstructing Three-dimensional Structure of Underlying Triaxial Dark Halos From Xray and Sunyaev-Zel'dovich Effect Observations of Galaxy Clusters
While the use of galaxy clusters as {\it tools} to probe cosmology is
established, their conventional description still relies on the spherical
and/or isothermal models that were proposed more than 20 years ago. We present,
instead, a deprojection method to extract their intrinsic properties from X-ray
and Sunyaev--Zel'dovich effect observations in order to improve our
understanding of cluster physics. First we develop a theoretical model for the
intra-cluster gas in hydrostatic equilibrium in a triaxial dark matter halo
with a constant axis ratio. In this theoretical model, the gas density profiles
are expressed in terms of the intrinsic properties of the dark matter halos.
Then, we incorporate the projection effect into the gas profiles, and show that
the gas surface brightness profiles are expressed in terms of the
eccentricities and the orientation angles of the dark halos. For the practical
purpose of our theoretical model, we provide several empirical fitting formulae
for the gas density and temperature profiles, and also for the surface
brightness profiles relevant to X-ray and Sunyaev--Zel'dovich effect
observations. Finally, we construct a numerical algorithm to determine the halo
eccentricities and orientation angles using our model, and demonstrate that it
is possible in principle to reconstruct the 3D structures of the dark halos
from the X-ray and/or Sunyaev-Zel'dovich effect cluster data alone without
requiring priors such as weak lensing informations and without relying on such
restrictive assumptions as the halo axial symmetry about the line-of-sight.Comment: Accepted version, new discussions added, typos and minor mistakes
corrected, ApJ in press (2004, Feb. 1 scheduled, Vol. 601, No. 2 issue),26
pages, 7 postscript figure
OH(A-X) fluorescence from photodissociative excitation of HO2 at 157.5 nm
The OH(A-X) fluorescence from photodissociative excitation of HO2 by F2 laser photons (157.5 nm) was observed and compared with the OH fluorescence spectra of H2O2 and the O2+CH3OH mixture. The rotational population distributions of OH(A) were obtained from the fluorescence spectra. The most populated levels are J = 4 for photodissociative excitation of HO2, J = 20 for H2O2, and J = 21 for the O2+CH3OH mixture. The fluorescence from the gas mixture is attributed to the O + H recombination for which the atoms are produced from photodissociation of parent molecules
Confronting cold dark matter cosmologies with strong clustering of Lyman break galaxies at
We perform a detailed analysis of the statistical significance of a
concentration of Lyman break galaxies at recently discovered by
Steidel et al. (1997), using a series of N-body simulations with
particles in a (100\himpc)^3 comoving box. While the observed number density
of Lyman break galaxies at implies that they correspond to systems
with dark matter halos of \simlt 10^{12}M_\odot, the resulting clustering of
such objects on average is not strong enough to be reconciled with the
concentration if it is fairly common; we predict one similar concentration
approximately per () fields in three representative cold dark matter
models. Considering the current observational uncertainty of the frequency of
such clustering at , it would be premature to rule out the models, but
the future spectroscopic surveys in a dozen fields could definitely challenge
all the existing cosmological models a posteriori fitted to the universe.Comment: the final version which matchs that published in ApJ Letters (Feb
1998); compared with the previous versions, the predictions for the SCDM
model are slightly changed; Latex, 11 pages, including 3 ps figure
Can Geometric Test Probe the Cosmic Equation of State ?
Feasibility of the geometric test as a probe of the cosmic equation of state
of the dark energy is discussed assuming the future 2dF QSO sample. We examine
sensitivity of the QSO two-point correlation functions, which are theoretically
computed incorporating the light-cone effect and the redshift distortions, as
well as the nonlinear effect, to a bias model whose evolution is
phenomenologically parameterized. It is shown that the correlation functions
are sensitive on a mean amplitude of the bias and not to the speed of the
redshift evolution. We will also demonstrate that an optimistic geometric test
could suffer from confusion that a signal from the cosmological model can be
confused with that from a stochastic character of the bias.Comment: 11 pages, including 3 figures, accepted for publication in ApJ
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