scholarly journals Joint growth-rate measurements from redshift-space distortions and peculiar velocities in the 6dF Galaxy Survey

2020 ◽  
Vol 494 (3) ◽  
pp. 3275-3293 ◽  
Author(s):  
Caitlin Adams ◽  
Chris Blake
Keyword(s):  
Growth Rate ◽  
Large Scale ◽  
Likelihood Method ◽  
Distortion Parameter ◽  
Peculiar Velocities ◽  
Cross Covariance ◽  
Space Distortion ◽  
Standard Cosmological Model ◽  
Parameter Constraints ◽  
Field Galaxy

ABSTRACT We present a new model for the cross-covariance between galaxy redshift-space distortions and peculiar velocities. We combine this with the autocovariance models of both probes in a fully self-consistent, maximum-likelihood method, allowing us to extract enhanced cosmological parameter constraints. When applying our method to the 6-degree Field Galaxy Survey (6dFGS), our constraint on the growth rate of structure is $f\sigma _8 = 0.384 \pm 0.052 \rm {(stat)} \pm 0.061 \rm {(sys)}$ and our constraint for the redshift-space distortion parameter is $\beta = 0.289^{+0.044}_{-0.043} \rm {(stat)} \pm 0.049 \rm {(sys)}$. We find that the statistical uncertainty for the growth rate of structure is reduced by 64 per cent when using the complete covariance model compared to the redshift-space distortion autocovariance model and 50 per cent when compared to using the peculiar-velocity autocovariance model. Our constraints are consistent with those from the literature on combining multiple tracers of large-scale structure, as well as those from other 6dFGS analyses. Our measurement is also consistent with the standard cosmological model.

scholarly journals Measuring the cosmic bulk flow with 6dFGSv

2014 ◽  
Vol 11 (S308) ◽  
pp. 336-339 ◽  
Author(s):  
Christina Magoulas ◽  
Christopher Springob ◽  
Matthew Colless ◽  
Jeremy Mould ◽  
John Lucey ◽  
...  
Keyword(s):  
Velocity Field ◽  
Large Scale ◽  
Cosmological Parameters ◽  
Distortion Parameter ◽  
Peculiar Velocity ◽  
Peculiar Velocities ◽  
Redshift Surveys ◽  
Luminous Matter ◽  
The Galaxy ◽  
Space Distortion

AbstractWhile recent years have seen rapid growth in the number of galaxy peculiar velocity measurements, disagreements remain about the extent to which the peculiar velocity field - a tracer of the large-scale distribution of mass - agrees with both ΛCDM expectations and with velocity field models derived from redshift surveys. The 6dF Galaxy Survey includes peculiar velocities for nearly 9 000 early-type galaxies (6dFGSv), making it the largest and most homogeneous galaxy peculiar velocity sample to date. We have used the 6dFGS velocity field to determine the amplitude and scale of large-scale cosmic flows in the local universe and test standard cosmological models. We also compare the galaxy density and peculiar velocity fields to establish the distribution of dark and luminous matter and better constrain key cosmological parameters such as the redshift-space distortion parameter.

scholarly journals Joint analysis of 6dFGS and SDSS peculiar velocities for the growth rate of cosmic structure and tests of gravity

2020 ◽  
Vol 497 (1) ◽  
pp. 1275-1293 ◽  
Author(s):  
Khaled Said ◽  
Matthew Colless ◽  
Christina Magoulas ◽  
John R Lucey ◽  
Michael J Hudson
Keyword(s):  
Growth Rate ◽  
Large Scale ◽  
Mass Density ◽  
Hubble Constant ◽  
Growth Index ◽  
Sloan Digital Sky Survey ◽  
Joint Analysis ◽  
Density Parameter ◽  
Peculiar Velocities ◽  
Fluctuation Amplitude

ABSTRACT Measurement of peculiar velocities by combining redshifts and distance indicators is a powerful way to measure the growth rate of a cosmic structure and test theories of gravity at low redshift. Here we constrain the growth rate of the structure by comparing observed Fundamental Plane peculiar velocities for 15 894 galaxies from the 6dF Galaxy Survey (6dFGS) and Sloan Digital Sky Survey (SDSS) with predicted velocities and densities from the 2M++ redshift survey. We measure the velocity scale parameter $\beta \equiv {\Omega _{\rm m}^\gamma }/b = 0.372^{+0.034}_{-0.050}$ and $0.314^{+0.031}_{-0.047}$ for 6dFGS and SDSS, respectively, where Ωm is the mass density parameter, γ is the growth index, and b is the bias parameter normalized to the characteristic luminosity of galaxies, L*. Combining 6dFGS and SDSS, we obtain β = 0.341 ± 0.024, implying that the amplitude of the product of the growth rate and the mass fluctuation amplitude is fσ8 = 0.338 ± 0.027 at an effective redshift z = 0.035. Adopting Ωm = 0.315 ± 0.007, as favoured by Planck and using γ = 6/11 for General Relativity and γ = 11/16 for DGP gravity, we get $S_8(z=0) = \sigma _8 \sqrt{\Omega _{\rm m}/0.3} =0.637 \pm 0.054$ and 0.741 ± 0.062 for GR and DGP, respectively. This measurement agrees with other low-redshift probes of large-scale structure but deviates by more than 3σ from the latest Planck CMB measurement. Our results favour values of the growth index γ > 6/11 or a Hubble constant H0 > 70 km s−1 Mpc−1 or a fluctuation amplitude σ8 < 0.8 or some combination of these. Imminent redshift surveys such as Taipan, DESI, WALLABY, and SKA1-MID will help to resolve this tension by measuring the growth rate of cosmic structure to 1 per cent in the redshift range 0 < z < 1.

The 6dF Galaxy Survey: Mass and Motions in the Local Universe

2005 ◽  
Vol 216 ◽  
pp. 180-189
Author(s):  
Matthew Colless ◽  
Heath Jones ◽  
Lachlan Campbell ◽  
Daniel Burkey ◽  
Andy Taylor ◽  
...  
Keyword(s):  
Cosmological Parameters ◽  
Relevant Information ◽  
Local Universe ◽  
Distortion Parameter ◽  
Peculiar Velocities ◽  
Wide Range ◽  
Data Release ◽  
The Galaxy ◽  
The Status ◽  
Space Distortion

The 6dF Galaxy Survey will provide 167 000 redshifts and about 15000 peculiar velocities for galaxies over most of the southern sky out to about cz = 30000 km s--1. The survey is currently almost half complete, with the final observations due in mid-2005. An initial data release was made public in December 2002; the first third of the dataset will be released at the end of 2003, with the remaining thirds being released at the end of 2004 and 2005. The status of the survey, the survey database and other relevant information can be obtained from the 6dFGS web site at http://www.mso.anu.edu.au/6dFGS.In terms of constraining cosmological parameters, combining the 6dFGS redshift and peculiar velocity surveys will allow us to: (1) break the degeneracy between the redshift-space distortion parameter β = Ω0.6m/b and the galaxy-mass correlation parameter rg; (2) measure the four parameters Ag, Γ, β and rg with precisions of between 1% and 3%; (3) measure the variation of rg and b with scale to within a few percent over a wide range of scales.

The 6dFGS peculiar velocity field

2012 ◽  
Vol 8 (S289) ◽  
pp. 269-273
Author(s):  
Christopher M. Springob ◽  
Christina Magoulas ◽  
Matthew Colless ◽  
D. Heath Jones ◽  
Lachlan Campbell ◽  
...  
Keyword(s):  
Velocity Field ◽  
Gaussian Model ◽  
Density Field ◽  
Bulk Flow ◽  
Bayesian Probability ◽  
Distortion Parameter ◽  
Peculiar Velocity ◽  
Peculiar Velocities ◽  
Redshift Survey ◽  
Space Distortion

AbstractThe 6dF Galaxy Survey (6dFGS) is an all-southern-sky galaxy survey, including 125,000 redshifts and a Fundamental Plane (FP) subsample of 10,000 peculiar velocities. This makes 6dFGS the largest peculiar-velocity sample to date. We have fitted the FP with a tri-variate Gaussian model using a maximum-likelihood approach, and derive the Bayesian probability distribution of the peculiar velocity for each of the 10,000 galaxies. We fit models of the velocity field, including comparisons to the field predicted from the redshift-survey density field, to derive the values of the redshift-space distortion parameter β, the bulk flow and the residual bulk flow in excess of that predicted from the density field. We compare these results to those derived by other authors and discuss the cosmological implications.

Large‐Scale Power Spectrum and Cosmological Parameters from SFI Peculiar Velocities

1999 ◽  
Vol 523 (1) ◽  
pp. 1-15 ◽  
Author(s):  
Wolfram Freudling ◽  
Idit Zehavi ◽  
Luiz N. da Costa ◽  
Avishai Dekel ◽  
Amiram Eldar ◽  
...  
Keyword(s):  
Power Spectrum ◽  
Large Scale ◽  
Cosmological Parameters ◽  
Peculiar Velocities

scholarly journals Large-Scale Flows in the Local Universe

1996 ◽  
Vol 168 ◽  
pp. 175-182 ◽  
Author(s):  
D.S. Mathewson ◽  
V.L. Ford
Keyword(s):  
Large Scale ◽  
Velocity Measurements ◽  
Local Universe ◽  
Peculiar Velocities ◽  
Redshift Surveys ◽  
Density Maps ◽  
The Universe ◽  
Great Wall ◽  
Great Attractor ◽  
Streaming Flow

Peculiar velocity measurements of 2500 southern spiral galaxies show large-scale flows in the direction of the Hydra-Centaurus clusters which fully participate in the flow themselves. The flow is not uniform over this region and seems to be associated with the denser regions which participate in the flow of amplitude about 400km/s. In the less dense regions the flow is small or non-existent. This makes the flow quite asymmetric and inconsistent with that expected from large-scale, parallel streaming flow that includes all galaxies out to 6000km/s as previously thought. The flow cannot be modelled by a Great Attractor at 4300km/s or the Centaurus clusters at 3500km/s. Indeed, from the density maps derived from the redshift surveys of “optical” and IRAS galaxies, it is difficult to see how the mass concentrations can be responsible particularly as they themselves participate in the flow. These results bring into question the generally accepted reason for the peculiar velocities of galaxies that they arise solely as a consequence of infall into the dense regions of the universe. To the N. of the Great Attractor region, the flow increases and shows no sign of diminishing out to the redshift limit of 8000km/s in this direction. We may have detected flow in the nearest section of the Great Wall.

scholarly journals Sampling weights in multilevel modelling: an investigation using PISA sampling structures

2021 ◽  
Vol 9 (1) ◽  
Author(s):  
Julia Mang ◽  
Helmut Küchenhoff ◽  
Sabine Meinck ◽  
Manfred Prenzel
Keyword(s):  
Hierarchical Models ◽  
Large Scale ◽  
Practical Importance ◽  
Multilevel Modelling ◽  
Likelihood Method ◽  
Multilevel Regression ◽  
Sampling Weights ◽  
International Student Assessment ◽  
Software Packages ◽  
Software Programs

Abstract Background Standard methods for analysing data from large-scale assessments (LSA) cannot merely be adopted if hierarchical (or multilevel) regression modelling should be applied. Currently various approaches exist; they all follow generally a design-based model of estimation using the pseudo maximum likelihood method and adjusted weights for the corresponding hierarchies. Specifically, several different approaches to using and scaling sampling weights in hierarchical models are promoted, yet no study has compared them to provide evidence of which method performs best and therefore should be preferred. Furthermore, different software programs implement different estimation algorithms, leading to different results. Objective and method In this study, we determine based on a simulation, the estimation procedure showing the smallest distortion to the actual population features. We consider different estimation, optimization and acceleration methods, and different approaches on using sampling weights. Three scenarios have been simulated using the statistical program R. The analyses have been performed with two software packages for hierarchical modelling of LSA data, namely Mplus and SAS. Results and conclusions The simulation results revealed three weighting approaches performing best in retrieving the true population parameters. One of them implies using only level two weights (here: final school weights) and is because of its simple implementation the most favourable one. This finding should provide a clear recommendation to researchers for using weights in multilevel modelling (MLM) when analysing LSA data, or data with a similar structure. Further, we found only little differences in the performance and default settings of the software programs used, with the software package Mplus providing slightly more precise estimates. Different algorithm starting settings or different accelerating methods for optimization could cause these distinctions. However, it should be emphasized that with the recommended weighting approach, both software packages perform equally well. Finally, two scaling techniques for student weights have been investigated. They provide both nearly identical results. We use data from the Programme for International Student Assessment (PISA) 2015 to illustrate the practical importance and relevance of weighting in analysing large-scale assessment data with hierarchical models.

scholarly journals Testing the effect of H0 on fσ8 tension using a Gaussian Process method

2020 ◽  
Author(s):  
En-Kun Li ◽  
Minghui Du ◽  
Zhi-Huan Zhou ◽  
Hongchao Zhang ◽  
Lixin Xu
Keyword(s):  
Growth Rate ◽  
Dark Energy ◽  
Cosmological Constant ◽  
Gaussian Process ◽  
Dark Energy Model ◽  
Hubble Space Telescope ◽  
Λcdm Model ◽  
Space Distortion ◽  
Best Fit ◽  
Process Method

Abstract Using the fσ8(z) redshift space distortion (RSD) data, the $\sigma _8^0-\Omega _m^0$ tension is studied utilizing a parameterization of growth rate f(z) = Ωm(z)γ. Here, f(z) is derived from the expansion history H(z) which is reconstructed from the observational Hubble data applying the Gaussian Process method. It is found that different priors of H0 have great influences on the evolution curve of H(z) and the constraint of $\sigma _8^0-\Omega _m^0$. When using a larger H0 prior, the low redshifts H(z) deviate significantly from that of the ΛCDM model, which indicates that a dark energy model different from the cosmological constant can help to relax the H0 tension problem. The tension between our best-fit values of $\sigma _8^0-\Omega _m^0$ and that of the Planck 2018 ΛCDM (PLA) will disappear (less than 1σ) when taking a prior for H0 obtained from PLA. Moreover, the tension exceeds 2σ level when applying the prior H0 = 73.52 ± 1.62 km/s/Mpc resulted from the Hubble Space Telescope photometry. By comparing the $S_8 -\Omega _m^0$ planes of our method with the results from KV450+DES-Y1, we find that using our method and applying the RSD data may be helpful to break the parameter degeneracies.

scholarly journals Large-Scale Structure in the Universe: Spatial Distribution and Peculiar Velocities

1987 ◽  
Vol 124 ◽  
pp. 335-348
Author(s):  
Neta A. Bahcall
Keyword(s):  
Dark Matter ◽  
Spatial Distribution ◽  
Large Scale ◽  
Large Scale Structure ◽  
Scale Structure ◽  
Clusters Of Galaxies ◽  
Large Scale Structures ◽  
Peculiar Velocities ◽  
Scale Structures ◽  
The Universe

The evidence for the existence of very large scale structures, ∼ 100h−1Mpc in size, as derived from the spatial distribution of clusters of galaxies is summarized. Detection of a ∼ 2000 kms−1 elongation in the redshift direction in the distribution of the clusters is also described. Possible causes of the effect are peculiar velocities of clusters on scales of 10–100h−1Mpc and geometrical elongation of superclusters. If the effect is entirely due to the peculiar velocities of clusters, then superclusters have masses of order 1016.5M⊙ and may contain a larger amount of dark matter than previously anticipated.

scholarly journals Addressing the Haze: The Role of Local Traditional Cultures and Islamic Teachings

ICR Journal ◽  
2018 ◽  
Vol 9 (1) ◽  
pp. 97-100
Author(s):  
Shahino Mah Abdullah
Keyword(s):  
Growth Rate ◽  
Forest Fires ◽  
Large Scale ◽  
Land Use Changes ◽  
Airborne Particles ◽  
Health Economy ◽  
Crop Growth Rate ◽  
The World ◽  
Related Mortality

The most frequent transboundary haze in the world takes place in Southeast Asia. It is usually caused by land-use changes, open burning, peat combustion, wildfires, and other farming activities. Serious haze occurred in 1983, 1997, 2005, 2006, 2009, 2010, 2013, 2015 and 2016, originating from large-scale forest fires in western Sumatra and southern Kalimantan, Indonesia. It caused adverse effects to locals as well as neighbouring countries, affecting their health, economy, agriculture, and biodiversity. Among the serious effects of haze are increased respiratory-related mortality due to toxic airborne particles, jet crashs and ship collisions due to restricted visibility, reduction of crop growth rate due to limited solar radiation, and extinction of endangered primates due to habitat loss. Neighbouring countries like Malaysia and Singapore sometimes have to close schools to prevent people from being exposed to air pollution, and its consequent respiratory ailments.  

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