1,376 research outputs found
Environmental control study of space vehicles. Part III - Thermal control techniques and systems
General analysis for space vehicle thermal control systems and technique
Probing Dark Energy with Baryonic Acoustic Oscillations from Future Large Galaxy Redshift Surveys
We show that the measurement of the baryonic acoustic oscillations in large
high redshift galaxy surveys offers a precision route to the measurement of
dark energy. The cosmic microwave background provides the scale of the
oscillations as a standard ruler that can be measured in the clustering of
galaxies, thereby yielding the Hubble parameter and angular diameter distance
as a function of redshift. This, in turn, enables one to probe dark energy. We
use a Fisher matrix formalism to study the statistical errors for redshift
surveys up to z=3 and report errors on cosmography while marginalizing over a
large number of cosmological parameters including a time-dependent equation of
state. With redshifts surveys combined with cosmic microwave background
satellite data, we achieve errors of 0.037 on Omega_x, 0.10 on w(z=0.8), and
0.28 on dw(z)/dz for cosmological constant model. Models with less negative
w(z) permit tighter constraints. We test and discuss the dependence of
performance on redshift, survey conditions, and fiducial model. We find results
that are competitive with the performance of future supernovae Ia surveys. We
conclude that redshift surveys offer a promising independent route to the
measurement of dark energy.Comment: submitted to ApJ, 24 pages, LaTe
The Correlation Function in Redshift Space: General Formula with Wide-angle Effects and Cosmological Distortions
A general formula for the correlation function in redshift space is derived
in linear theory. The formula simultaneously includes wide-angle effects and
cosmological distortions. The formula is applicable to any pair with arbitrary
angle between lines of sight, and arbitrary redshifts, , ,
which are not necessarily small. The effects of the spatial curvature both on
geometry and on fluctuation spectrum are properly taken into account, and thus
our formula holds in a Friedman-Lema\^{\i}tre universe with arbitrary
cosmological parameters and . We illustrate the pattern
of the resulting correlation function with several models, and also show that
validity region of the conventional distant observer approximation is .Comment: 45 pages including 9 figures, To Appear in Astrophys. J. 535 (2000
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
Exploring Large-scale Structure with Billions of Galaxies
We consider cosmological applications of galaxy number density correlations
to be inferred from future deep and wide multi-band optical surveys. We mostly
focus on very large scales as a probe of possible features in the primordial
power spectrum. We find the proposed survey of the Large Synoptic Survey
Telescope may be competitive with future all-sky CMB experiments over a broad
range of scales. On very large scales the inferred power spectrum is robust to
photometric redshift errors, and, given a sufficient number density of
galaxies, to angular variations in dust extinction and photometric calibration
errors. We also consider other applications, such as constraining dark energy
with the two CMB-calibrated standard rulers in the matter power spectrum, and
controlling the effect of photometric redshift errors to facilitate the
interpretation of cosmic shear data. We find that deep photometric surveys over
wide area can provide constraints that are competitive with spectroscopic
surveys in small volumes.Comment: 11 pages, 7 figures, ApJ accepted, references added, expanded
discussion in Sec. 3.
The construction of identities in narratives about serious leisure occupations
Engagement in occupation contributes to the shaping of identity throughout the human life. The act of telling about such engagement involves interaction based on symbolic meaning; the speaker constructing an identity by conveying how the occupation is personally meaningful. This study explored meaning in narratives told by people who engage in serious leisure occupations. A total of 78 narratives were extracted from interviews with 17 people who invest considerable time and other resources into their leisure. Analysis focused on the content, structure and performance of each narrative in order to explore meaning. The meanings were organised into a framework based around three dimensions: the located self, the active self and the changing self. Each dimension has facets that the individual might emphasise, constructing a unique identity. The framework offers a structured basis for conceptualising how occupation contributes to the shaping of the internalised self and the socially situated identity
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]
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