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.

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 2MTF – IV. A bulk flow measurement of the local Universe

2014 ◽  
Vol 445 (1) ◽  
pp. 402-413 ◽  
Author(s):  
Tao Hong ◽  
Christopher M. Springob ◽  
Lister Staveley-Smith ◽  
Morag I. Scrimgeour ◽  
Karen L. Masters ◽  
...  
Keyword(s):  
Flow Measurement ◽  
Bulk Flow ◽  
Local Universe

scholarly journals Cosmological bulk flow in the QCDM model: (in)consistency with ΛCDM

2021 ◽  
Vol 504 (1) ◽  
pp. 1304-1319
Author(s):  
A Salehi ◽  
M Yarahmadi ◽  
S Fathi ◽  
Kazuharu Bamba
Keyword(s):  
Cold Dark Matter ◽  
Bulk Flow ◽  
Microwave Background ◽  
Local Universe ◽  
Peculiar Velocities ◽  
Large Bulk ◽  
Likelihood Analysis ◽  
Type Ia ◽  
The Universe ◽  
Good Agreement

ABSTRACT We study the bulk flow of the local universe with Type Ia supernova data (a compilation of Union2 and Pantheon data) in the spatially flat homogeneous and isotropic space–time. In particular, we take the so-called QCDM models, which consist of cold dark matter (CDM) and a Q-component described by a scalar field with its self-interactions determined by an exponential potential. We use different cumulative redshift slices of the Union2 and Pantheon catalogues. A maximum-likelihood analysis of peculiar velocities confirms that, at low redshifts 0.015 < z < 0.1, the bulk flow is moving in the $l=272^{+17}_{-17}, b=33^{+12}_{-12}$, and $302^{+20}_{-20},3^{+10}_{-10}$ directions with $v _\mathrm{bulk} = 225^{+38}_{-35}$ and $246^{+64}_{-46}$ km s−1 for the Pantheon and Union2 data respectively, in good agreement with the direction of the cosmic microwave background dipole and with a number of previous studies at 1σ. However, for high redshifts 0.1 < z < 0.2, we get $v _\mathrm{bulk} = 708^{+110}_{-110}$ and $v_\mathrm{bulk}=1014^{+86}_{-114}\,\text{km\,s}^{-1}$ towards l = 318 ± 10°, b = −15 ± 9° and $l=254^{+16}_{-14},\ b=6^{+7}_{-10}$ for the Pantheon and Union2 data respectively. This indicates that for low redshifts our results are approximately consistent with the ΛCDM model; however, for high redshifts they disagree with ΛCDM and support the results of those studies that report a large bulk flow for the universe.

scholarly journals The autocorrelation analysis of deep galaxy samples

1978 ◽  
Vol 79 ◽  
pp. 280-280
Author(s):  
S. Phillipps
Keyword(s):  
Correlation Function ◽  
Small Area ◽  
Angular Diameter ◽  
Selection Function ◽  
Autocorrelation Analysis ◽  
Galaxy Distribution ◽  
Royal Observatory ◽  
The Galaxy ◽  
Point Correlation ◽  
Point Correlation Function

The two point correlation function w(θ) has been evaluated for the galaxies measured by the COSMOS machine at the Royal Observatory, Edinburgh, in an area of about 2 square degrees on a 2 hour exposure J plate and a 2 hour exposure R plate (Phillipps, S., Fong, R., Ellis, R.S., Fall, S.M. and MacGillivray, H.T., 1977, Mon. Not. R. astr. Soc., in press). in each case w(θ) is found to be in agreement with the form w = Aθ−0.8 found previously by Peebles and coworkers. Since the samples are not magnitude limited the selection function, i.e. the distribution in distance, was determined by using models of the galaxy distribution to fit the observed angular diameter counts. However, when these selection functions are used to scale the amplitudes found for our samples, the amplitudes are found to be lower than those expected from Peebles' results by a factor of about 3. We consider that this is likely to be due to a lack of clusters in the small area of sky which we have studied: analysis of further areas should show whether this is the case.

scholarly journals Methods for cluster cosmology and application to the SDSS in preparation for DES Year 1 release

2019 ◽  
Vol 488 (4) ◽  
pp. 4779-4800 ◽  
Author(s):  
M Costanzi ◽  
E Rozo ◽  
M Simet ◽  
Y Zhang ◽  
A E Evrard ◽  
...  
Keyword(s):  
Cold Dark Matter ◽  
Cosmological Parameters ◽  
Acoustic Oscillation ◽  
Big Bang ◽  
Sloan Digital Sky Survey ◽  
Selection Function ◽  
Mass Relation ◽  
Data Set ◽  
Dark Energy Survey ◽  
Future Work

ABSTRACT We implement the first blind analysis of cluster abundance data to derive cosmological constraints from the abundance and weak lensing signal of redMaPPer clusters in the Sloan Digital Sky Survey (SDSS). We simultaneously fit for cosmological parameters and the richness–mass relation of the clusters. For a flat Λ cold dark matter cosmological model with massive neutrinos, we find $S_8 \equiv \sigma _{8}(\Omega _\mathrm{ m}/0.3)^{0.5}=0.79^{+0.05}_{-0.04}$. This value is both consistent and competitive with that derived from cluster catalogues selected in different wavelengths. Our result is also consistent with the combined probes analyses by the Dark Energy Survey (DES), the Kilo-Degree Survey (KiDS), and with the cosmic microwave background (CMB) anisotropies as measured by Planck. We demonstrate that the cosmological posteriors are robust against variation of the richness–mass relation model and to systematics associated with the calibration of the selection function. In combination with baryon acoustic oscillation data and big bang nucleosynthesis data (Cooke et al.), we constrain the Hubble rate to be h = 0.66 ± 0.02, independent of the CMB. Future work aimed at improving our understanding of the scatter of the richness–mass relation has the potential to significantly improve the precision of our cosmological posteriors. The methods described in this work were developed for use in the forthcoming analysis of cluster abundances in the DES. Our SDSS analysis constitutes the first part of a staged-unblinding analysis of the full DES data set.

scholarly journals Massive neutrinos leave fingerprints on cosmic voids

2019 ◽  
Vol 488 (3) ◽  
pp. 4413-4426 ◽  
Author(s):  
Christina D Kreisch ◽  
Alice Pisani ◽  
Carmelita Carbone ◽  
Jia Liu ◽  
Adam J Hawken ◽  
...  
Keyword(s):  
Correlation Function ◽  
Cold Dark Matter ◽  
Opposite Effect ◽  
Cosmological Parameters ◽  
Neutrino Masses ◽  
Point Correlation ◽  
Point Correlation Function ◽  
Massive Neutrinos ◽  
Cosmic Voids ◽  
Simulation Volume

ABSTRACT Do void statistics contain information beyond the tracer 2-point correlation function? Yes! As we vary the sum of the neutrino masses, we find void statistics contain information absent when using just tracer 2-point statistics. Massive neutrinos uniquely affect cosmic voids. We explore their impact on void clustering using both the DEMNUni and MassiveNuS simulations. For voids, neutrino effects depend on the observed void tracers. As the neutrino mass increases, the number of small voids traced by cold dark matter particles increases and the number of large voids decreases. Surprisingly, when massive, highly biased, haloes are used as tracers, we find the opposite effect. The scale at which voids cluster, as well as the void correlation, is similarly sensitive to the sum of neutrino masses and the tracers. This scale-dependent trend is not due to simulation volume or halo density. The interplay of these signatures in the void abundance and clustering leaves a distinct fingerprint that could be detected with observations and potentially help break degeneracies between different cosmological parameters. This paper paves the way to exploit cosmic voids in future surveys to constrain the mass of neutrinos.

scholarly journals From correlation functions to event shapes in QCD

2021 ◽  
Vol 2021 (2) ◽  
Author(s):  
D. Chicherin ◽  
J. M. Henn ◽  
E. Sokatchev ◽  
K. Yan
Keyword(s):  
Correlation Function ◽  
Correlation Functions ◽  
Event Shape ◽  
Proof Of Concept ◽  
Yang Mills ◽  
Point Correlation ◽  
Point Correlation Function ◽  
Event Shapes ◽  
A Charge ◽  
Conserved Currents

Abstract We present a method for calculating event shapes in QCD based on correlation functions of conserved currents. The method has been previously applied to the maximally supersymmetric Yang-Mills theory, but we demonstrate that supersymmetry is not essential. As a proof of concept, we consider the simplest example of a charge-charge correlation at one loop (leading order). We compute the correlation function of four electromagnetic currents and explain in detail the steps needed to extract the event shape from it. The result is compared to the standard amplitude calculation. The explicit four-point correlation function may also be of interest for the CFT community.

scholarly journals A two-point correlation function for Galactic halo stars

2011 ◽  
Vol 417 (3) ◽  
pp. 2206-2215 ◽  
Author(s):  
A. P. Cooper ◽  
S. Cole ◽  
C. S. Frenk ◽  
A. Helmi
Keyword(s):  
Correlation Function ◽  
Galactic Halo ◽  
Halo Stars ◽  
Point Correlation ◽  
Point Correlation Function
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