45 research outputs found
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: 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
Non-parametric directionality analysis: extension for removal of a single common predictor and application to time series
BACKGROUND: The ability to infer network structure from multivariate neuronal signals is central to computational neuroscience. Directed network analyses typically use parametric approaches based on auto-regressive (AR) models, where networks are constructed from estimates of AR model parameters. However, the validity of using low order AR models for neurophysiological signals has been questioned. A recent article introduced a non-parametric approach to estimate directionality in bivariate data, non-parametric approaches are free from concerns over model validity.
NEW METHOD: We extend the non-parametric framework to include measures of directed conditional independence, using scalar measures that decompose the overall partial correlation coefficient summatively by direction, and a set of functions that decompose the partial coherence summatively by direction. A time domain partial correlation function allows both time and frequency views of the data to be constructed. The conditional independence estimates are conditioned on a single predictor.
RESULTS: The framework is applied to simulated cortical neuron networks and mixtures of Gaussian time series data with known interactions. It is applied to experimental data consisting of local field potential recordings from bilateral hippocampus in anaesthetised rats.
COMPARISON WITH EXISTING METHOD(S): The framework offers a non-parametric approach to estimation of directed interactions in multivariate neuronal recordings, and increased flexibility in dealing with both spike train and time series data.
CONCLUSIONS: The framework offers a novel alternative non-parametric approach to estimate directed interactions in multivariate neuronal recordings, and is applicable to spike train and time series data
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 transition to large-scale cosmic homogeneity
We have made the largest-volume measurement to date of the transition to
large-scale homogeneity in the distribution of galaxies. We use the WiggleZ
survey, a spectroscopic survey of over 200,000 blue galaxies in a cosmic volume
of ~1 (Gpc/h)^3. A new method of defining the 'homogeneity scale' is presented,
which is more robust than methods previously used in the literature, and which
can be easily compared between different surveys. Due to the large cosmic depth
of WiggleZ (up to z=1) we are able to make the first measurement of the
transition to homogeneity over a range of cosmic epochs. The mean number of
galaxies N(<r) in spheres of comoving radius r is proportional to r^3 within
1%, or equivalently the fractal dimension of the sample is within 1% of D_2=3,
at radii larger than 71 \pm 8 Mpc/h at z~0.2, 70 \pm 5 Mpc/h at z~0.4, 81 \pm 5
Mpc/h at z~0.6, and 75 \pm 4 Mpc/h at z~0.8. We demonstrate the robustness of
our results against selection function effects, using a LCDM N-body simulation
and a suite of inhomogeneous fractal distributions. The results are in
excellent agreement with both the LCDM N-body simulation and an analytical LCDM
prediction. We can exclude a fractal distribution with fractal dimension below
D_2=2.97 on scales from ~80 Mpc/h up to the largest scales probed by our
measurement, ~300 Mpc/h, at 99.99% confidence.Comment: 21 pages, 16 figures, accepted for publication in MNRA
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Conceptualising the drivers of ultra-processed food production and consumption and their environmental impacts: A group model-building exercise
Using group model building we developed a series of causal loop diagrams identifying the environmental impacts of ultra-processed food (UPF) systems, and underlying system drivers, which was subsequently validated against the peer-reviewed literature. The final conceptual model displays the commercial, biological and social drivers of the UPF system, and the impacts on environmental sub-systems including climate, land, water and waste. It displays complex interactions between various environmental impacts, demonstrating how changes to one component of the system could have flow-on effects on other components. Trade-offs and uncertainties are discussed. The model has a wide range of applications including informing the design of quantitative analyses, identifying research gaps and potential policy trade-offs resulting from a reduction of ultra-processed food production and consumption
The Canada-UK Deep Submillimetre Survey VIII: Source Identifications in the 3-hour field
We present optical, near-infrared and radio observations of the 3-hour field
of the Canada-UK Deep Submillimetre Survey. Of the 27 submillimetre sources in
the field, nine have secure identifications with either a radio source or a
near-IR source. We show that the percentage of sources with secure
identifications in the CUDSS is consistent with that found for the bright `8
mJy' submillimetre survey, once allowance is made for the different
submillimetre and radio flux limits. Of the 14 secure identifications in the
two CUDSS fields, eight are VROs or EROs, five have colours typical of normal
galaxies, and one is a radio source which has not yet been detected at
optical/near-IR wavelengths. Eleven of the identifications have optical/near-IR
structures which are either disturbed or have some peculiarity which suggests
that the host galaxy is part of an interacting system. One difference between
the CUDSS results and the results from the 8-mJy survey is the large number of
low-redshift objects in the CUDSS; we give several arguments why these are
genuine low-redshift submillimetre sources rather than being gravitational
lenses which are gravitationally amplifying a high- submillimetre source. We
construct a diagram for various classes of high-redshift galaxy and show
that the SCUBA galaxies are on average less luminous than classical radio
galaxies, but are very similar in both their optical/IR luminosities and their
colours to the host galaxies of the radio sources detected in Jy radio
surveys.Comment: accepted for publication in MNRAS, 18 pages, full-resolution versions
of Figure 1 and 2 can be found at
http://www.astro.cf.ac.uk/groups/cosmo/papers.htm
The Fourteenth Data Release of the Sloan Digital Sky Survey: First Spectroscopic Data from the extended Baryon Oscillation Spectroscopic Survey and from the second phase of the Apache Point Observatory Galactic Evolution Experiment
The fourth generation of the Sloan Digital Sky Survey (SDSS-IV) has been in
operation since July 2014. This paper describes the second data release from
this phase, and the fourteenth from SDSS overall (making this, Data Release
Fourteen or DR14). This release makes public data taken by SDSS-IV in its first
two years of operation (July 2014-2016). Like all previous SDSS releases, DR14
is cumulative, including the most recent reductions and calibrations of all
data taken by SDSS since the first phase began operations in 2000. New in DR14
is the first public release of data from the extended Baryon Oscillation
Spectroscopic Survey (eBOSS); the first data from the second phase of the
Apache Point Observatory (APO) Galactic Evolution Experiment (APOGEE-2),
including stellar parameter estimates from an innovative data driven machine
learning algorithm known as "The Cannon"; and almost twice as many data cubes
from the Mapping Nearby Galaxies at APO (MaNGA) survey as were in the previous
release (N = 2812 in total). This paper describes the location and format of
the publicly available data from SDSS-IV surveys. We provide references to the
important technical papers describing how these data have been taken (both
targeting and observation details) and processed for scientific use. The SDSS
website (www.sdss.org) has been updated for this release, and provides links to
data downloads, as well as tutorials and examples of data use. SDSS-IV is
planning to continue to collect astronomical data until 2020, and will be
followed by SDSS-V.Comment: SDSS-IV collaboration alphabetical author data release paper. DR14
happened on 31st July 2017. 19 pages, 5 figures. Accepted by ApJS on 28th Nov
2017 (this is the "post-print" and "post-proofs" version; minor corrections
only from v1, and most of errors found in proofs corrected