scholarly journals Gaussianization of peculiar velocities and bulk flow measurement

2021 ◽  
Vol 21 (10) ◽  
pp. 242
Author(s):  
Fei Qin
Keyword(s):  
Measurement Errors ◽  
Flow Measurement ◽  
Velocity Fields ◽  
Density Field ◽  
Bulk Flow ◽  
Line Of Sight ◽  
Distance Ratio ◽  
Field Techniques ◽  
Peculiar Velocities ◽  
Point Correlation

Abstract The line-of-sight peculiar velocities are good indicators of the gravitational fluctuation of the density field. Techniques have been developed to extract cosmological information from the peculiar velocities in order to test cosmological models. These techniques include measuring cosmic flow, measuring two-point correlation and power spectrum of the peculiar velocity fields, and reconstructing the density field using peculiar velocities. However, some measurements from these techniques are biased due to the non-Gaussianity of the estimated peculiar velocities. Therefore, we rely on the 2MTF survey to explore a power transform that can Gaussianize the estimated peculiar velocities. We find a tight linear relation between the transformation parameters and the measurement errors of log-distance ratio. To show an example for the implementation of Gaussianized peculiar velocities in cosmology, we develop a bulk flow estimator and estimate bulk flow from the Gaussianized peculiar velocities. We use 2MTF mocks to test the algorithm, and we find the algorithm yields unbiased measurements. We also find this technique gives smaller measurement errors compared to other techniques. In Galactic coordinates, at the depth of 30 h −1 Mpc, we measure a bulk flow of 332 ± 27 km s−1 in the direction (l,b) = (293° ± 5°, 13° ± 4°). The measurement is consistent with the ΛCDM prediction.

scholarly journals Cosmic Flow Measurement and Mock Sampling Algorithm of Cosmicflows-4 Tully−Fisher Catalog

2021 ◽  
Vol 922 (1) ◽  
pp. 59
Author(s):  
Fei Qin ◽  
David Parkinson ◽  
Cullan Howlett ◽  
Khaled Said
Keyword(s):  
Flow Measurement ◽  
Cold Dark Matter ◽  
Bulk Flow ◽  
Selection Function ◽  
Local Universe ◽  
Sampling Algorithm ◽  
Model Predictions ◽  
Point Correlation ◽  
Point Correlation Function ◽  
Future Work

Abstract Measurements of cosmic flows enable us to test whether cosmological models can accurately describe the evolution of the density field in the nearby universe. In this paper, we measure the low-order kinematic moments of the cosmic flow field, namely bulk flow and shear moments, using the Cosmicflows-4 Tully−Fisher catalog (CF4TF). To make accurate cosmological inferences with the CF4TF sample, it is important to make realistic mock catalogs. We present the mock sampling algorithm of CF4TF. These mocks can accurately realize the survey geometry and luminosity selection function, enabling researchers to explore how these systematics affect the measurements. These mocks can also be further used to estimate the covariance matrix and errors of the power spectrum and two-point correlation function in future work. In this paper, we use the mocks to test the cosmic flow estimator and find that the measurements are unbiased. The measured bulk flow in the local universe is 376 ± 23 (error) ± 183 (cosmic variance) km s−1 at depth d MLE = 35 Mpc h −1, to the Galactic direction of (l, b) = (298° ± 3°, −6° ± 3°). Both the measured bulk and shear moments are consistent with the concordance Λ Cold Dark Matter cosmological model predictions.

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.

scholarly journals Wide-angle effects for peculiar velocities

2020 ◽  
Vol 499 (1) ◽  
pp. 893-905
Author(s):  
Emanuele Castorina ◽  
Martin White
Keyword(s):  
Correlation Function ◽  
Cross Correlation ◽  
Density Field ◽  
Line Of Sight ◽  
Wide Angle ◽  
Fourier Space ◽  
Translational Invariance ◽  
Peculiar Velocities ◽  
Redshift Surveys ◽  
The Galaxy

ABSTRACT The line-of-sight peculiar velocities of galaxies contribute to their observed redshifts, breaking the translational invariance of galaxy clustering down to a rotational invariance around the observer. This becomes important when the line-of-sight direction varies significantly across a survey, leading to what are known as ‘wide-angle’ effects in redshift-space distortions. Wide-angle effects will also be present in measurements of the momentum field, i.e. the galaxy density-weighted velocity field, in upcoming peculiar velocity surveys. In this work, we study how wide-angle effects modify the predicted correlation function and power spectrum for momentum statistics, both in autocorrelation and in cross-correlation with the density field. Using both linear theory and the Zel'dovich approximation, we find that deviations from the plane-parallel limit are large and could become important in data analysis for low-redshift surveys. We point out that even multipoles in the cross-correlation between density and momentum are non-zero regardless of the choice of line of sight, and therefore contain new cosmological information that could be exploited. We discuss configuration space, Fourier space, and spherical analyses; providing exact expressions in each case rather than relying on an expansion in small angles. We hope these expressions will be of use in the analysis of upcoming surveys for redshift-space distortions and peculiar velocities.

scholarly journals Cosmic flows in the nearby Universe: new peculiar velocities from SNe and cosmological constraints

2020 ◽  
Vol 498 (2) ◽  
pp. 2703-2718 ◽  
Author(s):  
Supranta S Boruah ◽  
Michael J Hudson ◽  
Guilhem Lavaux
Keyword(s):  
Velocity Field ◽  
Velocity Fields ◽  
Bulk Flow ◽  
Peculiar Velocity ◽  
Cosmological Constraints ◽  
Peculiar Velocities ◽  
Type Ia ◽  
Galaxy Redshift ◽  
Ia Supernovae ◽  
Distance Indicators

ABSTRACT The peculiar velocity field offers a unique way to probe dark matter density field on large scales at low redshifts. In this work, we have compiled a new sample of 465 peculiar velocities from low redshift ($z$ < 0.067) Type Ia supernovae. We compare the reconstructed velocity field derived from the 2M++ galaxy redshift compilation to the supernovae, the SFI++ and the 2MTF Tully–Fisher distance catalogues. We used a forward method to jointly infer the distances and the velocities of distance indicators by comparing the observations to the reconstruction. Comparison of the reconstructed peculiar velocity fields to observations allows us to infer the cosmological parameter combination fσ8, and the bulk flow velocity arising from outside the survey volume. The residual bulk flow arising from outside the 2M++ volume is inferred to be $171^{+11}_{-11}$ km s−1 in the direction l = 301° ± 4° and b = 0° ± 3°. We obtain fσ8 = 0.400 ± 0.017, equivalent to S8 ≈ σ8(Ωm/0.3)0.55 = 0.776 ± 0.033, which corresponds to an approximately $4{{\ \rm per\ cent}}\,$ statistical uncertainty on the value of fσ8. Our inferred value is consistent with other low redshift results in the literature.

scholarly journals Cosmological parameters from the comparison of peculiar velocities with predictions from the 2M++ density field

2014 ◽  
Vol 11 (S308) ◽  
pp. 318-321
Author(s):  
Michael J. Hudson ◽  
Jonathan Carrick ◽  
Stephen J. Turnbull ◽  
Guilhem Lavaux
Keyword(s):  
Cosmic Microwave Background ◽  
Local Group ◽  
Cosmological Parameters ◽  
Density Field ◽  
Bulk Flow ◽  
Microwave Background ◽  
Peculiar Velocity ◽  
Peculiar Velocities ◽  
Best Fit ◽  
Good Agreement

AbstractUsing redshifts from the 2M++ redshift compilation, we reconstruct the density of galaxies within 200 h−1 Mpc, and compare the predicted peculiar velocities Tully-Fisher and SNe peculiar velocities. The comparison yields a best-fit value of β ≡ Ωm0.55/b* = 0.431 ± 0.021, suggesting Ωm0.55σ8,lin = 0.401 ± 0.024, in good agreement with other probes. The predicted peculiar velocity of the Local Group from sources within the 2M++ volume is 540 ± 40 km s−1, towards l = 268° ± 4°, b = 38° ± 6°, which is misaligned by only 10° with the Cosmic Microwave Background dipole. To account for sources outside the 2M++ volume, we fit simultaneously for β* and an external bulk flow in our analysis. The external bulk flow has a velocity of 159 ± 23 km s−1 towards l = 304° ± 11°, b6° ± 13°.

Pipeline Diagnostics With Ultrasonic Meters

2016 ◽  
Author(s):  
Nicole Gailey ◽  
Noman Rasool
Keyword(s):  
Real Time ◽  
Measurement Errors ◽  
Flow Measurement ◽  
Detection System ◽  
Leak Detection ◽  
The United States ◽  
Time Data ◽  
Critical System ◽  
Detection Systems ◽  
Transient Models

Canada and the United States have vast energy resources, supported by thousands of kilometers (miles) of pipeline infrastructure built and maintained each year. Whether the pipeline runs through remote territory or passing through local city centers, keeping commodities flowing safely is a critical part of day-to-day operation for any pipeline. Real-time leak detection systems have become a critical system that companies require in order to provide safe operations, protection of the environment and compliance with regulations. The function of a leak detection system is the ability to identify and confirm a leak event in a timely and precise manner. Flow measurement devices are a critical input into many leak detection systems and in order to ensure flow measurement accuracy, custody transfer grade liquid ultrasonic meters (as defined in API MPMS chapter 5.8) can be utilized to provide superior accuracy, performance and diagnostics. This paper presents a sample of real-time data collected from a field install base of over 245 custody transfer grade liquid ultrasonic meters currently being utilized in pipeline leak detection applications. The data helps to identify upstream instrumentation anomalies and illustrate the abilities of the utilization of diagnostics within the liquid ultrasonic meters to further improve current leak detection real time transient models (RTTM) and pipeline operational procedures. The paper discusses considerations addressed while evaluating data and understanding the importance of accuracy within the metering equipment utilized. It also elaborates on significant benefits associated with the utilization of the ultrasonic meter’s capabilities and the importance of diagnosing other pipeline issues and uncertainties outside of measurement errors.

scholarly journals Galaxy Motions in the Nearby Universe

1996 ◽  
Vol 168 ◽  
pp. 143-155
Author(s):  
John P. Huchra
Keyword(s):  
Virgo Cluster ◽  
Velocity Fields ◽  
Density Field ◽  
Current Status ◽  
Microwave Background ◽  
History Of ◽  
Measured Flow ◽  
Nearby Galaxies ◽  
Cluster 2 ◽  
Hubble Flow

In this paper we review the history of the search for and study of the motions of nearby galaxies with respect to the Hubble Flow. The current status of the field is that (1) convincing infall has been detected into dense clusters, especially the Virgo cluster, (2) the microwave background direction is moderately well aligned with the measured flow nearby but not apparently on larger scales, and (3) there is good but not perfect consistency between the nearby density fields and velocity fields. Particular problems exist in the different Ω's required to fit the density field derived from optically selected and IRAS (60μ) selected galaxy samples.

scholarly journals The Anglo-Australian Redshift Survey

1983 ◽  
Vol 104 ◽  
pp. 175-175
Author(s):  
J. Bean ◽  
G. Efstathiou ◽  
R. S. Ellis ◽  
B. A. Peterson ◽  
T. Shanks ◽  
...  
Keyword(s):  
Correlation Function ◽  
Luminosity Function ◽  
Large Scale ◽  
Peculiar Velocities ◽  
Point Correlation ◽  
Point Correlation Function ◽  
Redshift Survey ◽  
Density Inhomogeneities ◽  
The Universe

The aim of the survey is to sample a relatively large, randomly chosen volume of the Universe in order to study the large-scale distribution of galaxies using the two-point correlation function, the peculiar velocities between galaxy pairs and to provide an estimate of the galaxian luminosity function that is unaffected by density inhomogeneities and Virgo infall.

scholarly journals Acquisition of a 3 min, two-dimensional glacier velocity field with terrestrial radar interferometry

2017 ◽  
Vol 63 (240) ◽  
pp. 629-636 ◽  
Author(s):  
DENIS VOYTENKO ◽  
TIMOTHY H. DIXON ◽  
DAVID M. HOLLAND ◽  
RYAN CASSOTTO ◽  
IAN M. HOWAT ◽  
...  
Keyword(s):  
Velocity Field ◽  
Flow Field ◽  
Feature Tracking ◽  
High Spatial Resolution ◽  
Velocity Fields ◽  
Radar Interferometry ◽  
Line Of Sight ◽  
Two Dimensional ◽  
Outlet Glacier ◽  
Glacier Velocity

ABSTRACTOutlet glaciers undergo rapid spatial and temporal changes in flow velocity during calving events. Observing such changes requires both high temporal and high spatial resolution methods, something now possible with terrestrial radar interferometry. While a single such radar provides line-of-sight velocity, two radars define both components of the horizontal flow field. To assess the feasibility of obtaining the two-dimensional (2-D) flow field, we deployed two terrestrial radar interferometers at Jakobshavn Isbrae, a major outlet glacier on Greenland's west coast, in the summer of 2012. Here, we develop and demonstrate a method to combine the line-of-sight velocity data from two synchronized radars to produce a 2-D velocity field from a single (3 min) interferogram. Results are compared with the more traditional feature-tracking data obtained from the same radar, averaged over a longer period. We demonstrate the potential and limitations of this new dual-radar approach for obtaining high spatial and temporal resolution 2-D velocity fields at outlet glaciers.

scholarly journals Evolving Features of Hβ Doppler Velocity Fields at Sites of Flares

1993 ◽  
Vol 141 ◽  
pp. 267-270
Author(s):  
Wei Li ◽  
Guoxiang Ai ◽  
Hongqi Zhang
Keyword(s):  
Velocity Field ◽  
Active Regions ◽  
Velocity Fields ◽  
Time Sequence ◽  
Line Of Sight ◽  
Doppler Velocity

AbstractWe analyzed eight active regions with more than 600 flare kernels and ribbons, and relevant time sequence Hβ chromospheric Dopplergrams. These data showed that during several hours prior to the flares, the velocity field evolves so that the sites of the flare kernels and ribbons become close to the inversion line of the velocity field. This result holds regardless of whether or not the flare sites are wholly located in blue-shifted areas, or are far from the the inversion line of the line-of-sight velocity field, or are partly within red-shifted areas.

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