501 research outputs found
The WiggleZ dark energy survey
The accelerating expansion of the universe, attributed to "dark energy", has no accepted theoretical explanation. The origin of this phenomenon unambiguously implicates new physics via a novel form of matter exerting negative pressure or an alteration to Einstein's general relativity. These profound consequences have inspired a new generation of cosmological surveys that will measure the influence of dark energy using various techniques. One of the forerunners is the WiggleZ Survey at the Anglo-Australian Telescope, a new large-scale high-redshift galaxy survey that is now 50% complete and scheduled to finish in 2010. The WiggleZ project is aiming to map the cosmic expansion history using delicate features in the galaxy clustering pattern imprinted 13.7 billion years ago. In this article we outline the survey design and context, and predict the science highlights
The WiggleZ Dark Energy Survey: Star-formation in UV-luminous galaxies from their luminosity functions
We present the ultraviolet (UV) luminosity function of galaxies from the
GALEX Medium Imaging Survey with measured spectroscopic redshifts from the
first data release of the WiggleZ Dark Energy Survey. This sample selects
galaxies with high star formation rates: at 0.6 < z < 0.9 the median star
formation rate is at the upper 95th percentile of optically-selected (r<22.5)
galaxies and the sample contains about 50 per cent of all NUV < 22.8, 0.6 < z <
0.9 starburst galaxies within the volume sampled.
The most luminous galaxies in our sample (-21.0>M_NUV>-22.5) evolve very
rapidly with a number density declining as (1+z)^{5\pm 1} from redshift z = 0.9
to z = 0.6. These starburst galaxies (M_NUV<-21 is approximately a star
formation rate of 30 \msuny) contribute about 1 per cent of cosmic star
formation over the redshift range z=0.6 to z=0.9. The star formation rate
density of these very luminous galaxies evolves rapidly, as (1+z)^{4\pm 1}.
Such a rapid evolution implies the majority of star formation in these large
galaxies must have occurred before z = 0.9.
We measure the UV luminosity function in 0.05 redshift intervals spanning
0.1<z<0.9, and provide analytic fits to the results. At all redshifts greater
than z=0.55 we find that the bright end of the luminosity function is not well
described by a pure Schechter function due to an excess of very luminous
(M_NUV<-22) galaxies. These luminosity functions can be used to create a radial
selection function for the WiggleZ survey or test models of galaxy formation
and evolution. Here we test the AGN feedback model in Scannapieco et al.
(2005), and find that this AGN feedback model requires AGN feedback efficiency
to vary with one or more of the following: stellar mass, star formation rate
and redshift.Comment: 27 pages; 13 pages without appendices. 22 figures; 11 figures in the
main tex
The WiggleZ Dark Energy Survey: improved distance measurements to z = 1 with reconstruction of the baryonic acoustic feature
We present significant improvements in cosmic distance measurements from the WiggleZ Dark Energy Survey, achieved by applying the reconstruction of the baryonic acoustic feature technique. We show using both data and simulations that the reconstruction technique can often be effective despite patchiness of the survey, significant edge effects and shot-noise. We investigate three redshift bins in the redshift range 0.2 < z < 1, and in all three find improvement after reconstruction in the detection of the baryonic acoustic feature and its usage as a standard ruler. We measure model-independent distance measures DV(rsfid/rs) of 1716 ± 83, 2221 ± 101, 2516 ± 86 Mpc (68 per cent CL) at effective redshifts z = 0.44, 0.6, 0.73, respectively, where DV is the volume-averaged distance, and rs is the sound horizon at the end of the baryon drag epoch. These significantly improved 4.8, 4.5 and 3.4 per cent accuracy measurements are equivalent to those expected from surveys with up to 2.5 times the volume of WiggleZ without reconstruction applied. These measurements are fully consistent with cosmologies allowed by the analyses of the Planck Collaboration and the Sloan Digital Sky Survey. We provide the DV(rsfid/rs) posterior probability distributions and their covariances. When combining these measurements with temperature fluctuations measurements of Planck, the polarization of Wilkinson Microwave Anisotropy Probe 9, and the 6dF Galaxy Survey baryonic acoustic feature, we do not detect deviations from a flat Λ cold dark matter (ΛCDM) model. Assuming this model, we constrain the current expansion rate to H₀ = 67.15 ± 0.98 km s⁻¹Mpc⁻¹. Allowing the equation of state of dark energy to vary, we obtain wDE = −1.080 ± 0.135. When assuming a curved ΛCDM model we obtain a curvature value of ΩK = −0.0043 ± 0.0047
The WiggleZ Dark Energy Survey: small-scale clustering of Lyman-break galaxies at z < 1
The WiggleZ Dark Energy Survey is a large-scale structure survey of intermediate-redshift ultraviolet-selected (UV-selected) emission-line galaxies scheduled to cover 1000 deg^2, spanning a broad redshift range 0.2 < z < 1.0 . The main scientific goal of the survey is the measurement of baryon acoustic oscillations (BAO) in the galaxy clustering pattern at a significantly higher redshift than previous studies. The BAO may be applied as a standard cosmological ruler to constrain dark energy models. Based on the first 20 per cent of the data set, we present initial results concerning the small-scale clustering of the WiggleZ targets, together with survey forecasts. The WiggleZ galaxy population possesses a clustering length r_0 = 4.40 ± 0.12 h^(−1) Mpc, which is significantly larger than z = 0 UV-selected samples, with a slope γ = 1.92 ± 0.08 . This clustering length is comparable to z = 3 Lyman-break galaxies with similar UV luminosities. The clustering strength of the sample increases with optical luminosity, UV luminosity and reddening rest-frame colour. The full survey, scheduled for completion in 2010, will map an effective volume V_eff ≈ 1 Gpc^3 (evaluated at a scale k = 0.15 h Mpc^(−1)) and will measure the angular diameter distance and Hubble expansion rates in three redshift bins with accuracies of ≈5 per cent. We will determine the value of a constant dark energy equation-of-state parameter, wcons, with a higher precision than existing supernovae observations using an entirely independent technique. The WiggleZ and supernova measurements lie in highly complementary directions in the plane of w_(cons) and the matter density Ω_m. The forecast using the full combination of WiggleZ, supernova and cosmic microwave background (CMB) data sets is a marginalized error Δw_(cons) = 0.07 , providing a robust and precise measurement of the properties of dark energy including cross-checking of systematic errors
The WiggleZ Dark Energy Survey: Direct constraints on blue galaxy intrinsic alignments at intermediate redshifts
Correlations between the intrinsic shapes of galaxy pairs, and between the
intrinsic shapes of galaxies and the large-scale density field, may be induced
by tidal fields. These correlations, which have been detected at low redshifts
(z<0.35) for bright red galaxies in the Sloan Digital Sky Survey (SDSS), and
for which upper limits exist for blue galaxies at z~0.1, provide a window into
galaxy formation and evolution, and are also an important contaminant for
current and future weak lensing surveys. Measurements of these alignments at
intermediate redshifts (z~0.6) that are more relevant for cosmic shear
observations are very important for understanding the origin and redshift
evolution of these alignments, and for minimising their impact on weak lensing
measurements. We present the first such intermediate-redshift measurement for
blue galaxies, using galaxy shape measurements from SDSS and spectroscopic
redshifts from the WiggleZ Dark Energy Survey. Our null detection allows us to
place upper limits on the contamination of weak lensing measurements by blue
galaxy intrinsic alignments that, for the first time, do not require
significant model-dependent extrapolation from the z~0.1 SDSS observations.
Also, combining the SDSS and WiggleZ constraints gives us a long redshift
baseline with which to constrain intrinsic alignment models and contamination
of the cosmic shear power spectrum. Assuming that the alignments can be
explained by linear alignment with the smoothed local density field, we find
that a measurement of \sigma_8 in a blue-galaxy dominated, CFHTLS-like survey
would be contaminated by at most +/-0.02 (95% confidence level, SDSS and
WiggleZ) or +/-0.03 (WiggleZ alone) due to intrinsic alignments. [Abridged]Comment: 18 pages, 12 figures, accepted to MNRAS; v2 has correction to one
author's name, NO other changes; v3 has minor changes in explanation and
calculations, no significant difference in results or conclusions; v4 has an
additional footnote about model interpretation, no changes to
data/calculations/result
The WiggleZ Dark Energy Survey: the growth rate of cosmic structure since redshift z=0.9
We present precise measurements of the growth rate of cosmic structure for
the redshift range 0.1 < z < 0.9, using redshift-space distortions in the
galaxy power spectrum of the WiggleZ Dark Energy Survey. Our results, which
have a precision of around 10% in four independent redshift bins, are well-fit
by a flat LCDM cosmological model with matter density parameter Omega_m = 0.27.
Our analysis hence indicates that this model provides a self-consistent
description of the growth of cosmic structure through large-scale perturbations
and the homogeneous cosmic expansion mapped by supernovae and baryon acoustic
oscillations. We achieve robust results by systematically comparing our data
with several different models of the quasi-linear growth of structure including
empirical models, fitting formulae calibrated to N-body simulations, and
perturbation theory techniques. We extract the first measurements of the power
spectrum of the velocity divergence field, P_vv(k), as a function of redshift
(under the assumption that P_gv(k) = -sqrt[P_gg(k) P_vv(k)] where g is the
galaxy overdensity field), and demonstrate that the WiggleZ galaxy-mass
cross-correlation is consistent with a deterministic (rather than stochastic)
scale-independent bias model for WiggleZ galaxies for scales k < 0.3 h/Mpc.
Measurements of the cosmic growth rate from the WiggleZ Survey and other
current and future observations offer a powerful test of the physical nature of
dark energy that is complementary to distance-redshift measures such as
supernovae and baryon acoustic oscillations.Comment: 17 pages, 11 figures, accepted for publication by MNRA
The WiggleZ Dark Energy Survey: measuring the cosmic expansion history using the Alcock-Paczynski test and distant supernovae
Astronomical observations suggest that today's Universe is dominated by a
dark energy of unknown physical origin. One of the most notable consequences in
many models is that dark energy should cause the expansion of the Universe to
accelerate: but the expansion rate as a function of time has proven very
difficult to measure directly. We present a new determination of the cosmic
expansion history by combining distant supernovae observations with a
geometrical analysis of large-scale galaxy clustering within the WiggleZ Dark
Energy Survey, using the Alcock-Paczynski test to measure the distortion of
standard spheres. Our result constitutes a robust and non-parametric
measurement of the Hubble expansion rate as a function of time, which we
measure with 10-15% precision in four bins within the redshift range 0.1 < z <
0.9. We demonstrate that the cosmic expansion is accelerating, in a manner
independent of the parameterization of the cosmological model (although
assuming cosmic homogeneity in our data analysis). Furthermore, we find that
this expansion history is consistent with a cosmological-constant dark energy.Comment: 13 pages, 7 figures, accepted for publication by MNRA
The WiggleZ Dark Energy Survey: Survey Design and First Data Release
The WiggleZ Dark Energy Survey is a survey of 240,000 emission line galaxies
in the distant universe, measured with the AAOmega spectrograph on the 3.9-m
Anglo-Australian Telescope (AAT). The target galaxies are selected using
ultraviolet photometry from the GALEX satellite, with a flux limit of NUV<22.8
mag. The redshift range containing 90% of the galaxies is 0.2<z<1.0. The
primary aim of the survey is to precisely measure the scale of baryon acoustic
oscillations (BAO) imprinted on the spatial distribution of these galaxies at
look-back times of 4-8 Gyrs. Detailed forecasts indicate the survey will
measure the BAO scale to better than 2% and the tangential and radial acoustic
wave scales to approximately 3% and 5%, respectively.
This paper provides a detailed description of the survey and its design, as
well as the spectroscopic observations, data reduction, and redshift
measurement techniques employed. It also presents an analysis of the properties
of the target galaxies, including emission line diagnostics which show that
they are mostly extreme starburst galaxies, and Hubble Space Telescope images,
which show they contain a high fraction of interacting or distorted systems. In
conjunction with this paper, we make a public data release of data for the
first 100,000 galaxies measured for the project.Comment: Accepted by MNRAS; this has some figures in low resolution format.
Full resolution PDF version (7MB) available at
http://www.physics.uq.edu.au/people/mjd/pub/wigglez1.pdf The WiggleZ home
page is at http://wigglez.swin.edu.au
The WiggleZ Dark Energy Survey: the selection function and z=0.6 galaxy power spectrum
We report one of the most accurate measurements of the three-dimensional
large-scale galaxy power spectrum achieved to date, using 56,159 redshifts of
bright emission-line galaxies at effective redshift z=0.6 from the WiggleZ Dark
Energy Survey at the Anglo-Australian Telescope. We describe in detail how we
construct the survey selection function allowing for the varying target
completeness and redshift completeness. We measure the total power with an
accuracy of approximately 5% in wavenumber bands of dk=0.01 h/Mpc. A model
power spectrum including non-linear corrections, combined with a linear galaxy
bias factor and a simple model for redshift-space distortions, provides a good
fit to our data for scales k < 0.4 h/Mpc. The large-scale shape of the power
spectrum is consistent with the best-fitting matter and baryon densities
determined by observations of the Cosmic Microwave Background radiation. By
splitting the power spectrum measurement as a function of tangential and radial
wavenumbers we delineate the characteristic imprint of peculiar velocities. We
use these to determine the growth rate of structure as a function of redshift
in the range 0.4 < z < 0.8, including a data point at z=0.78 with an accuracy
of 20%. Our growth rate measurements are a close match to the self-consistent
prediction of the LCDM model. The WiggleZ Survey data will allow a wide range
of investigations into the cosmological model, cosmic expansion and growth
history, topology of cosmic structure, and Gaussianity of the initial
conditions. Our calculation of the survey selection function will be released
at a future date via our website wigglez.swin.edu.au.Comment: 21 pages, 22 figures, accepted for publication in MNRA
The WiggleZ Dark Energy Survey: measuring the cosmic growth rate with the two-point galaxy correlation function
The growth history of large-scale structure in the Universe is a powerful probe of the cosmological model, including the nature of dark energy. We study the growth rate of cosmic structure to redshift z = 0.9 using more than 162 000 galaxy redshifts from the WiggleZ Dark Energy Survey. We divide the data into four redshift slices with effective redshifts z = [0.2, 0.4, 0.6, 0.76] and in each of the samples measure and model the two-point galaxy correlation function in parallel and transverse directions to the line of sight. After simultaneously fitting for the galaxy bias factor we recover values for the cosmic growth rate which are consistent with our assumed Λcold dark matter (ΛCDM) input cosmological model, with an accuracy of around 20 per cent in each redshift slice. We investigate the sensitivity of our results to the details of the assumed model and the range of physical scales fitted, making close comparison with a set of N-body simulations for calibration. Our measurements are consistent with an independent power-spectrum analysis of a similar data set, demonstrating that the results are not driven by systematic errors. We determine the pairwise velocity dispersion of the sample in a non-parametric manner, showing that it systematically increases with decreasing redshift, and investigate the Alcock–Paczynski effects of changing the assumed fiducial model on the results. Our techniques should prove useful for current and future galaxy surveys mapping the growth rate of structure using the two-dimensional correlation function
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