4,183 research outputs found
Wide Angle Redshift Distortions Revisited
We explore linear redshift distortions in wide angle surveys from the point
of view of symmetries. We show that the redshift space two-point correlation
function can be expanded into tripolar spherical harmonics of zero total
angular momentum . The
coefficients of the expansion are analogous to the 's of
the angular power spectrum, and express the anisotropy of the redshift space
correlation function. Moreover, only a handful of are
non-zero: the resulting formulae reveal a hidden simplicity comparable to
distant observer limit. The depend on spherical Bessel
moments of the power spectrum and . In the plane parallel
limit, the results of \cite{Kaiser1987} and \cite{Hamilton1993} are recovered.
The general formalism is used to derive useful new expressions. We present a
particularly simple trigonometric polynomial expansion, which is arguably the
most compact expression of wide angle redshift distortions. These formulae are
suitable to inversion due to the orthogonality of the basis functions. An
alternative Legendre polynomial expansion was obtained as well. This can be
shown to be equivalent to the results of \cite{SzalayEtal1998}. The simplicity
of the underlying theory will admit similar calculations for higher order
statistics as well.Comment: 6 pages, 1 figure, ApJL submitte
An Inversion Method for Measuring Beta in Large Redshift Surveys
A precision method for determining the value of Beta= Omega_m^{0.6}/b, where
b is the galaxy bias parameter, is presented. In contrast to other existing
techniques that focus on estimating this quantity by measuring distortions in
the redshift space galaxy-galaxy correlation function or power spectrum, this
method removes the distortions by reconstructing the real space density field
and determining the value of Beta that results in a symmetric signal. To remove
the distortions, the method modifies the amplitudes of a Fourier plane-wave
expansion of the survey data parameterized by Beta. This technique is not
dependent on the small-angle/plane-parallel approximation and can make full use
of large redshift survey data. It has been tested using simulations with four
different cosmologies and returns the value of Beta to +/- 0.031, over a factor
of two improvement over existing techniques.Comment: 16 pages including 6 figures Submitted to The Astrophysical Journa
The European Chemical Society (EuChemS)
The European Chemical Society (EuChemS) coordinates the work of almost all the European Chemical Societies. As an organization, it provides an independent and authoritative voice on all matters relating to chemistry, and try to place chemistry at the heart of policy in Europe. Furthermore, EuChemS seeks to develop its members through various activities, workshops and awards. Particularly, EuChemS has fostered growth in its young members through the European Young Chemists′ Network. Beyond Europe, EuChemS has collaborated with various organizations in bringing chemistry out of the lab and into society in building a sustainable future for everyone.PostprintPeer reviewe
Measuring the galaxy power spectrum with future redshift surveys
Precision measurements of the galaxy power spectrum P(k) require a data
analysis pipeline that is both fast enough to be computationally feasible and
accurate enough to take full advantage of high-quality data. We present a
rigorous discussion of different methods of power spectrum estimation, with
emphasis on the traditional Fourier method, the linear (Karhunen-Loeve; KL),
and quadratic data compression schemes, showing in what approximations they
give the same result. To improve speed, we show how many of the advantages of
KL data compression and power spectrum estimation may be achieved with a
computationally faster quadratic method. To improve accuracy, we derive
analytic expressions for handling the integral constraint, since it is crucial
that finite volume effects are accurately corrected for on scales comparable to
the depth of the survey. We also show that for the KL and quadratic techniques,
multiple constraints can be included via simple matrix operations, thereby
rendering the results less sensitive to galactic extinction and mis-estimates
of the radial selection function. We present a data analysis pipeline that we
argue does justice to the increases in both quality and quantity of data that
upcoming redshift surveys will provide. It uses three analysis techniques in
conjunction: a traditional Fourier approach on small scales, a pixelized
quadratic matrix method on large scales and a pixelized KL eigenmode analysis
to probe anisotropic effects such as redshift-space distortions.Comment: Major revisions for clarity. Matches accepted ApJ version. 23 pages,
with 2 figs included. Color figure and links at
http://www.sns.ias.edu/~max/galpower.html (faster from the US), from
http://www.mpa-garching.mpg.de/~max/galpower.html (faster from Europe) or
from [email protected]
Baryon Acoustic Oscillations in 2D: Modeling Redshift-space Power Spectrum from Perturbation Theory
We present an improved prescription for matter power spectrum in redshift
space taking a proper account of both the non-linear gravitational clustering
and redshift distortion, which are of particular importance for accurately
modeling baryon acoustic oscillations (BAOs). Contrary to the models of
redshift distortion phenomenologically introduced but frequently used in the
literature, the new model includes the corrections arising from the non-linear
coupling between the density and velocity fields associated with two
competitive effects of redshift distortion, i.e., Kaiser and Finger-of-God
effects. Based on the improved treatment of perturbation theory for
gravitational clustering, we compare our model predictions with monopole and
quadrupole power spectra of N-body simulations, and an excellent agreement is
achieved over the scales of BAOs. Potential impacts on constraining dark energy
and modified gravity from the redshift-space power spectrum are also
investigated based on the Fisher-matrix formalism. We find that the existing
phenomenological models of redshift distortion produce a systematic error on
measurements of the angular diameter distance and Hubble parameter by 1~2%, and
the growth rate parameter by ~5%, which would become non-negligible for future
galaxy surveys. Correctly modeling redshift distortion is thus essential, and
the new prescription of redshift-space power spectrum including the non-linear
corrections can be used as an accurate theoretical template for anisotropic
BAOs.Comment: 18 pages, 10 figure
Radial Redshift Space Distortions
The radial component of the peculiar velocities of galaxies cause
displacements in their positions in redshift space. We study the effect of the
peculiar velocities on the linear redshift space two point correlation
function. Our analysis takes into account the radial nature of the redshift
space distortions and it highlights the limitations of the plane parallel
approximation. We consider the problem of determining the value of \beta and
the real space two point correlation function from the linear redshift space
two point correlation function. The inversion method proposed here takes into
account the radial nature of the redshift space distortions and can be applied
to magnitude limited redshift surveys that have only partial sky coverage.Comment: 26 pages including 11 figures, to appear in Ap
Determination of the Baryon Density from Large Scale Galaxy Redshift Surveys
We estimate the degree to which the baryon density, , can be
determined from the galaxy power spectrum measured from large scale galaxy
redshift surveys, and in particular, the Sloan Digital Sky Survey. A high
baryon density will cause wiggles to appear in the power spectrum, which should
be observable at the current epoch. We assume linear theory on scales and do not include the effects of redshift distortions, evolution,
or biasing. With an optimum estimate of to ,
the uncertainties in are roughly 0.07 and 0.016 in flat
and open () cosmological models, respectively. This result
suggests that it should be possible to test for consistency with big bang
nucleosynthesis estimates of if we live in an open universe.Comment: 23 Pages, 10 Postscript figure
Complete Treatment of Galaxy Two-Point Statistics: Gravitational Lensing Effects and Redshift-Space Distortions
We present a coherent theoretical framework for computing gravitational
lensing effects and redshift-space distortions in an inhomogeneous universe and
investigate their impacts on galaxy two-point statistics. Adopting the
linearized FRW metric, we derive the gravitational lensing and the generalized
Sachs-Wolfe effects that include the weak lensing distortion, magnification,
and time delay effects, and the redshift-space distortion, Sachs-Wolfe, and
integrated Sachs-Wolfe effects, respectively. Based on this framework, we first
compute their effects on observed source fluctuations, separating them as two
physically distinct origins: the volume effect that involves the change of
volume and is always present in galaxy two-point statistics, and the source
effect that depends on the intrinsic properties of source populations. Then we
identify several terms that are ignored in the standard method, and we compute
the observed galaxy two-point statistics, an ensemble average of all the
combinations of the intrinsic source fluctuations and the additional
contributions from the gravitational lensing and the generalized Sachs-Wolfe
effects. This unified treatment of galaxy two-point statistics clarifies the
relation of the gravitational lensing and the generalized Sachs-Wolfe effects
to the metric perturbations and the underlying matter fluctuations. For near
future dark energy surveys, we compute additional contributions to the observed
galaxy two-point statistics and analyze their impact on the anisotropic
structure. Thorough theoretical modeling of galaxy two-point statistics would
be not only necessary to analyze precision measurements from upcoming dark
energy surveys, but also provide further discriminatory power in understanding
the underlying physical mechanisms.Comment: 20 pages, 5 figures, Fig.4 corrected, appendix added, accepted for
publication in Physical Review
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