The improvements in the sensitivity of the gravitational wave(GW) network enable the detection of several large redshift GW sources by third-generation GW detectors. These advancements provide an independent method to...The improvements in the sensitivity of the gravitational wave(GW) network enable the detection of several large redshift GW sources by third-generation GW detectors. These advancements provide an independent method to probe the large-scale structure of the universe by using the clustering of the binary black holes(BBHs). The black hole catalogs are complementary to the galaxy catalogs because of large redshifts of GW events, which may imply that BBHs are a better choice than galaxies to probe the large-scale structure of the universe and cosmic evolution over a large redshift range. To probe the large-scale structure, we used the sky position of the BBHs observed by third-generation GW detectors to calculate the angular correlation function and the bias factor of the population of BBHs. This method is also statistically significant as 5000 BBHs are simulated. Moreover, for the third-generation GW detectors, we found that the bias factor can be recovered to within 33% with an observational time of ten years. This method only depends on the GW source-location posteriors;hence, it can be an independent method to reveal the formation mechanisms and origin of the BBH mergers compared to the electromagnetic method.展开更多
The size distributions of 2D and 3D Voronoi cells and of cells of Vp(2, 3),--2D cut of 3D Voronoi diagram--are explored, with the slngle-parameter (re-scaled) gamma distribution playing a central role in the analy...The size distributions of 2D and 3D Voronoi cells and of cells of Vp(2, 3),--2D cut of 3D Voronoi diagram--are explored, with the slngle-parameter (re-scaled) gamma distribution playing a central role in the analytical fitting. Observational evidence for a cellular universe is briefly reviewed. A simulated Vp(2, 3) map with galaxies lying on the cell boundaries is constructed to compare, as regards general appearance, with the observed CfA map of galaxies and voids, the parameters of the simulation being so chosen as to reproduce the largest observed void size.展开更多
A new way of probing the large-scale structure of the universe is proposed. Space is partitioned into cells the shape of rhombic dodecahedron. The cells are labelled 'filled' or 'empty' according as th...A new way of probing the large-scale structure of the universe is proposed. Space is partitioned into cells the shape of rhombic dodecahedron. The cells are labelled 'filled' or 'empty' according as they contain galaxies or not. The cell size is so chosen as to have nearly equal numbers of filled and empty cells for the given galaxy sample. Two observables on each cell are definable: the number of its like neighbors, n1, and a two-suffixed topological type τ, the suffixes being the numbers of its like and unlike neighbor-groups. The frequency distributions of n1 and T in the observed set of filled (empty) cells are then considered as indicators of the morphology of the set. The method is applied to the CfA catalogue of galaxies as an illustration. Despite its limited size, the data offers evidence 1) that the empty cells are more strongly clustered than the filled cells, and 2) that the filled cells, but not the empty cells, have a tendency to occur in sheets. Further directions of development both in theory and application are indicated.展开更多
Major interactions are known to trigger star formation in galaxies and alter their color.We study the major interactions in filaments and sheets using SDSS data to understand the influence of large-scale environments ...Major interactions are known to trigger star formation in galaxies and alter their color.We study the major interactions in filaments and sheets using SDSS data to understand the influence of large-scale environments on galaxy interactions.We identify the galaxies in filaments and sheets using the local dimension and also find the major pairs residing in these environments.The star formation rate(SFR) and color of the interacting galaxies as a function of pair separation are separately analyzed in filaments and sheets.The analysis is repeated for three volume limited samples covering different magnitude ranges.The major pairs residing in the filaments show a significantly higher SFR and bluer color than those residing in the sheets up to the projected pair separation of~50 kpc.We observe a complete reversal of this behavior for both the SFR and color of the galaxy pairs having a projected separation larger than 50 kpc.Some earlier studies report that the galaxy pairs align with the filament axis.Such alignment inside filaments indicates anisotropic accretion that may cause these differences.We do not observe these trends in the brighter galaxy samples.The pairs in filaments and sheets from the brighter galaxy samples trace relatively denser regions in these environments.The absence of these trends in the brighter samples may be explained by the dominant effect of the local density over the effects of the large-scale environment.展开更多
Using a uniform partitioning of cubic cells,we cover the total volume of aΛCDM cosmological simulation based on particles.We define a visualization cell as a spatial extension of the cubic cell,so that we collect all...Using a uniform partitioning of cubic cells,we cover the total volume of aΛCDM cosmological simulation based on particles.We define a visualization cell as a spatial extension of the cubic cell,so that we collect all simulation particles contained in this visualization cell to create a series of Cartesian plots in which the overdensity of matter is clearly visible.We then use these plots as input to a convolutional neural network(CNN)based on the Keras library and TensorFlow for image classification.To assign a class to each plot,we approximate the Hessian of the gravitational potential in the center of the cubic cells.Each selected cubic cell is then assigned a label of 1,2 or 3,depending on the number of positive eigenvalues obtained for the Householder reduction of the Hessian matrix.We apply the CNN to several models,including two models with different visualization volumes,one with a cell size of type L(large)and the other with a cell type S(small).A third model combines the plots of the previous L and S cell types.So far,we have mainly considered a slice parallel to the XY plane to make the plots.The last model is considered based on visualizations of cells that also include slices parallel to the ZX and ZY planes.We find that the accuracy in classification plots is acceptable,and the ability of the models to predict the class works well.These results allow us to demonstrate the aim of this paper,namely that the usual Cartesian plots contain enough information to identify the observed structures of the cosmic web.展开更多
We develop methods to extract key dark energy information from cosmic distance measurements including the BAO scales and supernova(SN) luminosity distances.Demonstrated using simulated data sets of the complete DESI,L...We develop methods to extract key dark energy information from cosmic distance measurements including the BAO scales and supernova(SN) luminosity distances.Demonstrated using simulated data sets of the complete DESI,LSST and Roman surveys designed for BAO and SN distance measurements,we show that using our method,the dynamical behavior of the energy,pressure,equation of state(with its time derivative) of dark energy and the cosmic deceleration function can all be accurately recovered from high-quality data,which allows for robust diagnostic tests for dark energy models.展开更多
Gamma-ray bursts(GRBs) are among the brightest objects in the Universe and, hence, can be observed up to a very high redshift. Properly calibrated empirical correlations between intensity and spectral correlations of ...Gamma-ray bursts(GRBs) are among the brightest objects in the Universe and, hence, can be observed up to a very high redshift. Properly calibrated empirical correlations between intensity and spectral correlations of GRBs can be used to estimate the cosmological parameters. However, the possibility of the evolution of GRBs with redshift is a long-standing puzzle. In this work, we used 162 long-duration GRBs to determine whether GRBs below and above a certain redshift have different properties. The GRBs are split into two groups, and we fit the Amati relation for each group separately. Our findings demonstrate that estimations of the Amati parameters for the two groups are substantially dissimilar. We perform simulations to investigate whether the selection effects could cause the difference. Our analysis shows that the differences may be either intrinsic or due to systematic errors in the data, and the selection effects are not their true origin. However, in-depth analysis with a new data set comprised of 119 long GRBs shows that intrinsic scatter may partly be responsible for such effects.展开更多
A significant excess of the stellar mass density at high redshift has been discovered from the early data release of James Webb Space Telescope(JWST),and it may require a high star formation efficiency.However,this wi...A significant excess of the stellar mass density at high redshift has been discovered from the early data release of James Webb Space Telescope(JWST),and it may require a high star formation efficiency.However,this will lead to large number density of ionizing photons in the epoch of reionization(EoR),so that the reionization history will be changed,which can arise tension with the current EoR observations.Warm dark matter(WDM),via the free streaming effect,can suppress the formation of small-scale structure as well as low-mass galaxies.This provides an effective way to decrease the ionizing photons when considering a large star formation efficiency in high-z massive galaxies without altering the cosmic reionization history.On the other hand,the constraints on the properties of WDM can be derived from the JWST observations.In this work,we study WDM as a possible solution to reconcile the JWST stellar mass density of high-z massive galaxies and reionization history.We find that,the JWST high-z comoving cumulative stellar mass density alone has no significant preference for either CDM or WDM model.But using the observational data of other stellar mass density measurements and reionization history,we obtain that the WDM particle mass with mw=0.51_(-0.12)^(+0.22) keV and star formation efficiency parameter f_(*)^(0)> 0.39 in 2σ confidence level can match both the JWST high-z comoving cumulative stellar mass density and the reionization history.展开更多
Fast Fourier transform based estimators are formulated for measuring momentum power spectra,including the auto power spectra of the momentum,the momentum divergence,and the cross spectrum of density fluctuation and mo...Fast Fourier transform based estimators are formulated for measuring momentum power spectra,including the auto power spectra of the momentum,the momentum divergence,and the cross spectrum of density fluctuation and momentum divergence.Algorithms using the third order Bettle-Lemariéscaling function to assign discrete objects to regular grids for fast Fourier transform are proposed to clean alias effects.Numerical experiments prove that the implementation can achieve sub-percent precision till close to the Nyquist frequency.The impact of removing bulk flow on the estimation of momentum power spectra is derived theoretically and verified numerically.Subtracting bulk flow has little effects at large scales but might induce meaningful differences in nonlinear regime,and probably it is not necessary to subtract bulk flow for samples which peculiar velocities are exact or sufficiently accurate.Momentum power spectra of dark matter samples from N-body simulation are measured and discussed.As expected,the prediction of the one loop Eulerian perturbation theory agrees with simulation only slightly better than the linear theory at z=0,but can be applied to higher redshift with improved accuracy.Measurements of simulation data and the one loop Eulerian theory both reveal that the momentum field contains strong rotational part,and there is a large stochastic component in the divergence of momentum which is not correlated with the density field.The three kinds of momentum power spectra have their own characteristics.展开更多
The pairwise velocity generating function G has a deep connection with both the pairwise velocity probability distribution function and modeling of redshift space distortion(RSD).Its implementation into RSD modeling i...The pairwise velocity generating function G has a deep connection with both the pairwise velocity probability distribution function and modeling of redshift space distortion(RSD).Its implementation into RSD modeling is often faciliated by expansion into a series of pairwise velocity moments(v^(n)_(12))-Motivated by the logrithmic transformation of the cosmic density field,we investigate an alternative expansion into series of pairwise velocity cumulants(v^(n)_(12))c.We numerically evaluate the convergence rate of the two expansions,with three 30723 particle simulations of the CosmicGrowth N-body simulation series.(1)We find that the cumulant expansion performs significantly better,for all the halo samples and redshifts investigated.(2)For modeling RSD at k||<O.1h Mpc^(-1),including only the n=1,2 cumulants is sufficient.(3)But for modeling RSD at k||=0.2h Mpc^(-1),we need and only need the n=1,2,3,4 cumulants.These results provide specific requirements on RSD modeling in terms of m-th order statistics of the large-scale structure.展开更多
We forecast the cosmological constraints of the neutral hydrogen(HI) intensity mapping(IM)technique with radio telescopes by assuming 1-year of observational time. The current and future radio telescopes that we consi...We forecast the cosmological constraints of the neutral hydrogen(HI) intensity mapping(IM)technique with radio telescopes by assuming 1-year of observational time. The current and future radio telescopes that we consider here are Five-hundred-meter Aperture Spherical radio Telescope(FAST), Baryon acoustic oscillations In Neutral Gas Observations(BINGO), and Square Kilometre Array phase Ⅰ(SKA-Ⅰ) single-dish experiments. We also forecast the combined constraints of the three radio telescopes with Planck. We find that the 1σ errors of(w0, wa) for BINGO, FAST and SKA-Ⅰ with respect to the fiducial values are respectively,(0.9293, 3.5792),(0.4083, 1.5878) and(0.3158, 0.4622). This is equivalent to(56.04%, 55.64%) and(66.02%, 87.09%) improvements in constraining(w0, wa) for FAST and SKA-Ⅰ respectively relative to BINGO. Simulations further show that SKA-Ⅰ will put more stringent constraints than both FAST and BINGO when each of the experiments is combined with Planck measurements. The 1σ errors for(w0, wa), BINGO + Planck, FAST + Planck and SKA-Ⅰ + Planck covariance matrices are respectively(0.0832, 0.3520),(0.0791, 0.3313) and(0.0678, 0.2679) implying there is an improvement in(w0, wa) constraints of(4.93%, 5.88%) for FAST + Planck relative to BINGO + Planck and an improvement of(18.51%, 23.89%) in constraining(w0, wa) for SKA-Ⅰ + Planck relative to BINGO + Planck. We also compared the performance of Planck data plus each single-dish experiment relative to Planck alone,and find that the reduction in(w0, wa) 1σ errors for each experiment plus Planck, respectively, imply the(w0, wa) constraints improvement of(22.96%, 8.45%),(26.76%, 13.84%) and(37.22%, 30.33%) for BINGO + Planck, FAST + Planck and SKA-Ⅰ + Planck relative to Planck alone. For the nine cosmological parameters in consideration, we find that there is a trade-off between SKA-Ⅰ and FAST in constraining cosmological parameters, with each experiment being more superior in constraining a particular set of parameters.展开更多
Based on the field theory of density fiuctuation under Newtonian gravity,we obtain analytically the nonlinear equation of 3-pt correlation functionζof galaxies in a homogeneous,isotropic,static universe.The density f...Based on the field theory of density fiuctuation under Newtonian gravity,we obtain analytically the nonlinear equation of 3-pt correlation functionζof galaxies in a homogeneous,isotropic,static universe.The density fiuctuation has been kept up to second order.By the Fry-Peebles ansatz and the Groth-Peebles ansatz,the equation ofζbecomes closed and differs from the Gaussian approximate equation.Using the boundary condition inferred from the data of SDSS,we obtain the solutionζ(r,u,θ)at fixed u=2,which exhibits a shallow U-shape along the angleθand,nevertheless,decreases monotonously along the radial r.We show its difference with the Gaussian solution.As a direct criterion of non-Gaussianity,the reduced Q(r,u,θ)deviates from the Gaussianity plane Q=1,exhibits a deeper U-shape alongθand varies weakly along r,agreeing with the observed data.展开更多
Applying functional differentiation to the density field with Newtonian gravity,we obtain the static,nonlinear equation of the three-point correlation functionζof galaxies to the third order density perturbations.We ...Applying functional differentiation to the density field with Newtonian gravity,we obtain the static,nonlinear equation of the three-point correlation functionζof galaxies to the third order density perturbations.We make the equation closed and perform renormalization of the mass and the Jeans wavenumber.Using the boundary condition inferred from observations,we obtain the third order solutionζ(r,u,θ)at fixed u=2,which is positive,exhibits a Ushape along the angleθ,and decreases monotonously along the radial r up to the range r≤30 h^(-1)Mpc in our computation.The corresponding reduced Q(r,u,θ)deviates from 1 of the Gaussian case,has a deeper U-shape alongθ,and varies non-monotonously along r.The third order solution agrees with the SDSS data of galaxies,quite close to the previous second order solution,especially at large scales.This indicates that the equations of correlation functions with increasing orders of density perturbation provide a stable description of the nonlinear galaxy system.展开更多
We examine the possibility of applying the baryonic acoustic oscillation reconstruction method to improve the neutrino massΣm_νconstraint.Thanks to the Gaussianization of the process,we demonstrate that the reconstr...We examine the possibility of applying the baryonic acoustic oscillation reconstruction method to improve the neutrino massΣm_νconstraint.Thanks to the Gaussianization of the process,we demonstrate that the reconstruction algorithm could improve the measurement accuracy by roughly a factor of two.On the other hand,the reconstruction process itself becomes a source of systematic error.While the algorithm is supposed to produce the displacement field from a density distribution,various approximations cause the reconstructed output to deviate on intermediate scales.Nevertheless,it is still possible to benefit from this Gaussianized field,given that we can carefully calibrate the“transfer function”between the reconstruction output and theoretical displacement divergence from simulations.The limitation of this approach is then set by the numerical stability of this transfer function.With an ensemble of simulations,we show that such systematic error could become comparable to statistical uncertainties for a DESI-like survey and be safely neglected for other less ambitious surveys.展开更多
Cross-correlating the data on neutral hydrogen(HⅠ)21 cm intensity mapping with galaxy surveys is an effective method to extract astrophysical and cosmological information.In this work,we investigate the cross-correla...Cross-correlating the data on neutral hydrogen(HⅠ)21 cm intensity mapping with galaxy surveys is an effective method to extract astrophysical and cosmological information.In this work,we investigate the cross-correlation of MeerKAT single-dish mode HⅠintensity mapping and China Space Station Telescope(CSST)spectroscopic galaxy surveys.We simulate a survey area of~300 deg~2 of MeerKAT and CSST surveys at z=0.5 using MultiDark N-body simulation.The PC A algorithm is applied to remove the foregrounds of HⅠintensity mapping,and signal compensation is considered to solve the signal loss problem in HⅠ-galaxy cross power spectrum caused by the foreground removal process.We find that from CSST galaxy auto and MeerKAT-CSST cross power spectra,the constraint accuracy of the parameter productΩ_(HⅠ)b_(HⅠ)r_(HⅠ,g)can reach~1%,which is about one order of magnitude higher than the current results.After performing the full MeerKAT HⅠintensity mapping survey with5000 deg~2 survey area,the accuracy can be enhanced to<0.3%.This implies that the MeerKAT-CSST cross-correlation can be a powerful tool to probe the cosmic HⅠproperty and the evolution of galaxies and the Universe.展开更多
The holographic dark energy models provide an alternative description of dark energy.These models are motivated by the possible application of the holographic principle to the dark energy problem.In this work,we prese...The holographic dark energy models provide an alternative description of dark energy.These models are motivated by the possible application of the holographic principle to the dark energy problem.In this work,we present a theoretical study of the one parameter Li holographic dark energy and the two parameter Barrow holographic dark energy models using configuration entropy of the matter distribution in the universe.The configuration entropy rate exhibits a distinct minimum at a specific scale factor that corresponds to the epoch,beyond which dark energy takes a driving role in the accelerated expansion of the universe.We find that the location of the minimum and magnitude of the entropy rate at the minimum are sensitive to the parameters of the models.We find the best fit relations between these quantities and the parameters of each model.We propose that these relations can be used to constrain the parameters of the holographic dark energy models from future observations such as the SKA.Our study suggests that the signature of a large quantum gravitational effect on the future event horizon can be detected from measurements of the configuration entropy of the matter distribution at multiple redshifts.展开更多
The China Space Station Telescope(CSST) photometric survey aims to perform a high spatial resolution(~0.″ 15)photometric imaging for the targets that cover a large sky area(~17,500 deg^(2)) and wide wavelength range(...The China Space Station Telescope(CSST) photometric survey aims to perform a high spatial resolution(~0.″ 15)photometric imaging for the targets that cover a large sky area(~17,500 deg^(2)) and wide wavelength range(from NUV to NIR). It expects to explore the properties of dark matter, dark energy, and other important cosmological and astronomical areas. In this work, we evaluate whether the filter design of the Multi-channel Imager(MCI), one of the five instruments of the CSST, can provide accurate photometric redshift(photoz) measurements with its nine medium-band filters to meet the relevant scientific objectives. We generate the mock data based on the COSMOS photometric redshift catalog with astrophysical and instrumental effects. The application of upper limit information of low signal-to-noise ratio data is adopted in the estimation of photoz. We investigate the dependency of photoz accuracy on the filter parameters, such as band position and width. We find that the current MCI filter design can achieve good photoz measurements with accuracy σ_(z)■ 0.017 and outlier fraction f_(c)■ 2.2%. It can effectively improve the photoz measurements of the main CSST survey using the Survey Camera to an accuracy σ_(z)■ 0.015 and outlier fraction f_(c)■ 1.5%. This indicates that the original MCI filters are proper for the photoz calibration.展开更多
We present an analysis of the fluctuation of the local Hubble flow using 350 galaxies in the Local Volume (D 〈 5 Mpc, hereafter LV) with accurate measurements of distances, positions and radial velocities, and comp...We present an analysis of the fluctuation of the local Hubble flow using 350 galaxies in the Local Volume (D 〈 5 Mpc, hereafter LV) with accurate measurements of distances, positions and radial velocities, and compare the results with the theoretical prediction of the local Hubble flow induced by density perturbations. This allows us to set a useful constraint on the local Ω parameters: ΩM - 0.6 and ΩA - 0.7, which may serve as compelling evidence for the existence of dark energy in the local Universe.展开更多
We study the connections between the pairwise velocity moment generating function G(k_(‖),r)and redshift space distortion(RSD)modeling.Here k_(‖)is the Fourier wavevector parallel to the line of sight,and r is the p...We study the connections between the pairwise velocity moment generating function G(k_(‖),r)and redshift space distortion(RSD)modeling.Here k_(‖)is the Fourier wavevector parallel to the line of sight,and r is the pair separation vector.We demonstrate its usage by two examples.(1)Besides the known relations between G and the RSD power spectrum(and the correlation function),we propose a new RSD statistics Ps(k_(‖),r_(丄))whose connection to G is convenient to evaluate numerically.(2)We then develop a fast method to numerically evaluate G,and apply it to a high resolution N-body simulation.We find that G(ln G)shows complicated dependence on k_(‖)beyond the linear and quadratic dependencies.This not only shows inaccuracy in some existing models and identifies sources of inaccuracy but also provides possible ways of improving the RSD modeling.Consequently,more comprehensive investigations on G are needed to fully explore the usage of G in RSD modeling.展开更多
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 ...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 nonGaussianity 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 theΛCDM prediction.展开更多
基金supported by the National Natural Science Foundation of China (grant Nos. 11922303, 119201003 and 12021003)supported by Hubei province Natural Science Fund for the Distinguished Young Scholars (No.2019CFA052)supported by CAS Project for Young Scientists in Basic Research YSBR-006。
文摘The improvements in the sensitivity of the gravitational wave(GW) network enable the detection of several large redshift GW sources by third-generation GW detectors. These advancements provide an independent method to probe the large-scale structure of the universe by using the clustering of the binary black holes(BBHs). The black hole catalogs are complementary to the galaxy catalogs because of large redshifts of GW events, which may imply that BBHs are a better choice than galaxies to probe the large-scale structure of the universe and cosmic evolution over a large redshift range. To probe the large-scale structure, we used the sky position of the BBHs observed by third-generation GW detectors to calculate the angular correlation function and the bias factor of the population of BBHs. This method is also statistically significant as 5000 BBHs are simulated. Moreover, for the third-generation GW detectors, we found that the bias factor can be recovered to within 33% with an observational time of ten years. This method only depends on the GW source-location posteriors;hence, it can be an independent method to reveal the formation mechanisms and origin of the BBH mergers compared to the electromagnetic method.
文摘The size distributions of 2D and 3D Voronoi cells and of cells of Vp(2, 3),--2D cut of 3D Voronoi diagram--are explored, with the slngle-parameter (re-scaled) gamma distribution playing a central role in the analytical fitting. Observational evidence for a cellular universe is briefly reviewed. A simulated Vp(2, 3) map with galaxies lying on the cell boundaries is constructed to compare, as regards general appearance, with the observed CfA map of galaxies and voids, the parameters of the simulation being so chosen as to reproduce the largest observed void size.
文摘A new way of probing the large-scale structure of the universe is proposed. Space is partitioned into cells the shape of rhombic dodecahedron. The cells are labelled 'filled' or 'empty' according as they contain galaxies or not. The cell size is so chosen as to have nearly equal numbers of filled and empty cells for the given galaxy sample. Two observables on each cell are definable: the number of its like neighbors, n1, and a two-suffixed topological type τ, the suffixes being the numbers of its like and unlike neighbor-groups. The frequency distributions of n1 and T in the observed set of filled (empty) cells are then considered as indicators of the morphology of the set. The method is applied to the CfA catalogue of galaxies as an illustration. Despite its limited size, the data offers evidence 1) that the empty cells are more strongly clustered than the filled cells, and 2) that the filled cells, but not the empty cells, have a tendency to occur in sheets. Further directions of development both in theory and application are indicated.
基金financial support from the SERB,DST,Government of India through the project CRG/2019/001110IUCAA,Pune for providing support through an associateship program+1 种基金IISER Tirupati for support through a postdoctoral fellowshipFunding for the SDSS and SDSS-Ⅱhas been provided by the Alfred P.Sloan Foundation,the U.S.Department of Energy,the National Aeronautics and Space Administration,the Japanese Monbukagakusho,the Max Planck Society,and the Higher Education Funding Council for England。
文摘Major interactions are known to trigger star formation in galaxies and alter their color.We study the major interactions in filaments and sheets using SDSS data to understand the influence of large-scale environments on galaxy interactions.We identify the galaxies in filaments and sheets using the local dimension and also find the major pairs residing in these environments.The star formation rate(SFR) and color of the interacting galaxies as a function of pair separation are separately analyzed in filaments and sheets.The analysis is repeated for three volume limited samples covering different magnitude ranges.The major pairs residing in the filaments show a significantly higher SFR and bluer color than those residing in the sheets up to the projected pair separation of~50 kpc.We observe a complete reversal of this behavior for both the SFR and color of the galaxy pairs having a projected separation larger than 50 kpc.Some earlier studies report that the galaxy pairs align with the filament axis.Such alignment inside filaments indicates anisotropic accretion that may cause these differences.We do not observe these trends in the brighter galaxy samples.The pairs in filaments and sheets from the brighter galaxy samples trace relatively denser regions in these environments.The absence of these trends in the brighter samples may be explained by the dominant effect of the local density over the effects of the large-scale environment.
基金support provided by the Laboratorio Nacional de Supercómputo del Sureste de México through grant No.O-2016/047。
文摘Using a uniform partitioning of cubic cells,we cover the total volume of aΛCDM cosmological simulation based on particles.We define a visualization cell as a spatial extension of the cubic cell,so that we collect all simulation particles contained in this visualization cell to create a series of Cartesian plots in which the overdensity of matter is clearly visible.We then use these plots as input to a convolutional neural network(CNN)based on the Keras library and TensorFlow for image classification.To assign a class to each plot,we approximate the Hessian of the gravitational potential in the center of the cubic cells.Each selected cubic cell is then assigned a label of 1,2 or 3,depending on the number of positive eigenvalues obtained for the Householder reduction of the Hessian matrix.We apply the CNN to several models,including two models with different visualization volumes,one with a cell size of type L(large)and the other with a cell type S(small).A third model combines the plots of the previous L and S cell types.So far,we have mainly considered a slice parallel to the XY plane to make the plots.The last model is considered based on visualizations of cells that also include slices parallel to the ZX and ZY planes.We find that the accuracy in classification plots is acceptable,and the ability of the models to predict the class works well.These results allow us to demonstrate the aim of this paper,namely that the usual Cartesian plots contain enough information to identify the observed structures of the cosmic web.
基金supported by the National Key R&D Program of China(2023YFA1607800,2023YFA1607803)the National Natural Science Foundation of China (NSFC,Grant Nos.11925303 and11890691)+3 种基金supported by the National Natural Science Foundation of China (NSFC,Grant No.12203062)by a CAS Project for Young Scientists in Basic Research (No.YSBR-092)supported by science research grants from the China Manned Space Project with No.CMS-CSST-2021-B01supported by the New Cornerstone Science Foundation through the XPLORER prize。
文摘We develop methods to extract key dark energy information from cosmic distance measurements including the BAO scales and supernova(SN) luminosity distances.Demonstrated using simulated data sets of the complete DESI,LSST and Roman surveys designed for BAO and SN distance measurements,we show that using our method,the dynamical behavior of the energy,pressure,equation of state(with its time derivative) of dark energy and the cosmic deceleration function can all be accurately recovered from high-quality data,which allows for robust diagnostic tests for dark energy models.
基金M.S.thanks DMRC for supportD.S.thanks the compeers of GD Goenka University for continuing assistance.
文摘Gamma-ray bursts(GRBs) are among the brightest objects in the Universe and, hence, can be observed up to a very high redshift. Properly calibrated empirical correlations between intensity and spectral correlations of GRBs can be used to estimate the cosmological parameters. However, the possibility of the evolution of GRBs with redshift is a long-standing puzzle. In this work, we used 162 long-duration GRBs to determine whether GRBs below and above a certain redshift have different properties. The GRBs are split into two groups, and we fit the Amati relation for each group separately. Our findings demonstrate that estimations of the Amati parameters for the two groups are substantially dissimilar. We perform simulations to investigate whether the selection effects could cause the difference. Our analysis shows that the differences may be either intrinsic or due to systematic errors in the data, and the selection effects are not their true origin. However, in-depth analysis with a new data set comprised of 119 long GRBs shows that intrinsic scatter may partly be responsible for such effects.
基金support of the National Key R&D Program of China No. 2022YFF0503404, 2020SKA0110402,MOST-2018YFE0120800,NSFC-11822305, NSFC-11773031,NSFC-11633004, NSFC-11473044, NSFC-11973047the CAS Project for Young Scientists in Basic Research (No. YSBR-092)+1 种基金the Chinese Academy of Sciences grants QYZDJ-SSWSLH017, XDB 23040100, and XDA15020200supported by the science research grants from the China Manned Space Project with NO.CMS-CSST-2021-B01 and CMS-CSST-2021-A01。
文摘A significant excess of the stellar mass density at high redshift has been discovered from the early data release of James Webb Space Telescope(JWST),and it may require a high star formation efficiency.However,this will lead to large number density of ionizing photons in the epoch of reionization(EoR),so that the reionization history will be changed,which can arise tension with the current EoR observations.Warm dark matter(WDM),via the free streaming effect,can suppress the formation of small-scale structure as well as low-mass galaxies.This provides an effective way to decrease the ionizing photons when considering a large star formation efficiency in high-z massive galaxies without altering the cosmic reionization history.On the other hand,the constraints on the properties of WDM can be derived from the JWST observations.In this work,we study WDM as a possible solution to reconcile the JWST stellar mass density of high-z massive galaxies and reionization history.We find that,the JWST high-z comoving cumulative stellar mass density alone has no significant preference for either CDM or WDM model.But using the observational data of other stellar mass density measurements and reionization history,we obtain that the WDM particle mass with mw=0.51_(-0.12)^(+0.22) keV and star formation efficiency parameter f_(*)^(0)> 0.39 in 2σ confidence level can match both the JWST high-z comoving cumulative stellar mass density and the reionization history.
基金the National Key R&D Program of China(Grant No.2018YFE0202900)the National Natural Science Foundation of China(Grant No.11573030)。
文摘Fast Fourier transform based estimators are formulated for measuring momentum power spectra,including the auto power spectra of the momentum,the momentum divergence,and the cross spectrum of density fluctuation and momentum divergence.Algorithms using the third order Bettle-Lemariéscaling function to assign discrete objects to regular grids for fast Fourier transform are proposed to clean alias effects.Numerical experiments prove that the implementation can achieve sub-percent precision till close to the Nyquist frequency.The impact of removing bulk flow on the estimation of momentum power spectra is derived theoretically and verified numerically.Subtracting bulk flow has little effects at large scales but might induce meaningful differences in nonlinear regime,and probably it is not necessary to subtract bulk flow for samples which peculiar velocities are exact or sufficiently accurate.Momentum power spectra of dark matter samples from N-body simulation are measured and discussed.As expected,the prediction of the one loop Eulerian perturbation theory agrees with simulation only slightly better than the linear theory at z=0,but can be applied to higher redshift with improved accuracy.Measurements of simulation data and the one loop Eulerian theory both reveal that the momentum field contains strong rotational part,and there is a large stochastic component in the divergence of momentum which is not correlated with the density field.The three kinds of momentum power spectra have their own characteristics.
基金funded by the National Natural Science Foundation of China(Grant No.11621303)。
文摘The pairwise velocity generating function G has a deep connection with both the pairwise velocity probability distribution function and modeling of redshift space distortion(RSD).Its implementation into RSD modeling is often faciliated by expansion into a series of pairwise velocity moments(v^(n)_(12))-Motivated by the logrithmic transformation of the cosmic density field,we investigate an alternative expansion into series of pairwise velocity cumulants(v^(n)_(12))c.We numerically evaluate the convergence rate of the two expansions,with three 30723 particle simulations of the CosmicGrowth N-body simulation series.(1)We find that the cumulant expansion performs significantly better,for all the halo samples and redshifts investigated.(2)For modeling RSD at k||<O.1h Mpc^(-1),including only the n=1,2 cumulants is sufficient.(3)But for modeling RSD at k||=0.2h Mpc^(-1),we need and only need the n=1,2,3,4 cumulants.These results provide specific requirements on RSD modeling in terms of m-th order statistics of the large-scale structure.
基金the DAAD (German Academic Exchange Service) scholarshipfinancial support from The African Institute for Mathematical Sciences, University of KwaZulu-Natal+1 种基金The Dar Es Salaam University College of Education, Tanzaniasupport from the National Research Foundation of South Africa (Grant Nos. 105925 and 110984)
文摘We forecast the cosmological constraints of the neutral hydrogen(HI) intensity mapping(IM)technique with radio telescopes by assuming 1-year of observational time. The current and future radio telescopes that we consider here are Five-hundred-meter Aperture Spherical radio Telescope(FAST), Baryon acoustic oscillations In Neutral Gas Observations(BINGO), and Square Kilometre Array phase Ⅰ(SKA-Ⅰ) single-dish experiments. We also forecast the combined constraints of the three radio telescopes with Planck. We find that the 1σ errors of(w0, wa) for BINGO, FAST and SKA-Ⅰ with respect to the fiducial values are respectively,(0.9293, 3.5792),(0.4083, 1.5878) and(0.3158, 0.4622). This is equivalent to(56.04%, 55.64%) and(66.02%, 87.09%) improvements in constraining(w0, wa) for FAST and SKA-Ⅰ respectively relative to BINGO. Simulations further show that SKA-Ⅰ will put more stringent constraints than both FAST and BINGO when each of the experiments is combined with Planck measurements. The 1σ errors for(w0, wa), BINGO + Planck, FAST + Planck and SKA-Ⅰ + Planck covariance matrices are respectively(0.0832, 0.3520),(0.0791, 0.3313) and(0.0678, 0.2679) implying there is an improvement in(w0, wa) constraints of(4.93%, 5.88%) for FAST + Planck relative to BINGO + Planck and an improvement of(18.51%, 23.89%) in constraining(w0, wa) for SKA-Ⅰ + Planck relative to BINGO + Planck. We also compared the performance of Planck data plus each single-dish experiment relative to Planck alone,and find that the reduction in(w0, wa) 1σ errors for each experiment plus Planck, respectively, imply the(w0, wa) constraints improvement of(22.96%, 8.45%),(26.76%, 13.84%) and(37.22%, 30.33%) for BINGO + Planck, FAST + Planck and SKA-Ⅰ + Planck relative to Planck alone. For the nine cosmological parameters in consideration, we find that there is a trade-off between SKA-Ⅰ and FAST in constraining cosmological parameters, with each experiment being more superior in constraining a particular set of parameters.
基金supported by NSFC Grant Nos.11675165,11633001 and 11961131007in part by the National Key RD Program of China(2021YFC2203100)。
文摘Based on the field theory of density fiuctuation under Newtonian gravity,we obtain analytically the nonlinear equation of 3-pt correlation functionζof galaxies in a homogeneous,isotropic,static universe.The density fiuctuation has been kept up to second order.By the Fry-Peebles ansatz and the Groth-Peebles ansatz,the equation ofζbecomes closed and differs from the Gaussian approximate equation.Using the boundary condition inferred from the data of SDSS,we obtain the solutionζ(r,u,θ)at fixed u=2,which exhibits a shallow U-shape along the angleθand,nevertheless,decreases monotonously along the radial r.We show its difference with the Gaussian solution.As a direct criterion of non-Gaussianity,the reduced Q(r,u,θ)deviates from the Gaussianity plane Q=1,exhibits a deeper U-shape alongθand varies weakly along r,agreeing with the observed data.
基金supported by NSFC(Grant Nos.11675165,11633001,and 11961131007)in part by the National Key RD Program of China(2021YFC2203100)。
文摘Applying functional differentiation to the density field with Newtonian gravity,we obtain the static,nonlinear equation of the three-point correlation functionζof galaxies to the third order density perturbations.We make the equation closed and perform renormalization of the mass and the Jeans wavenumber.Using the boundary condition inferred from observations,we obtain the third order solutionζ(r,u,θ)at fixed u=2,which is positive,exhibits a Ushape along the angleθ,and decreases monotonously along the radial r up to the range r≤30 h^(-1)Mpc in our computation.The corresponding reduced Q(r,u,θ)deviates from 1 of the Gaussian case,has a deeper U-shape alongθ,and varies non-monotonously along r.The third order solution agrees with the SDSS data of galaxies,quite close to the previous second order solution,especially at large scales.This indicates that the equations of correlation functions with increasing orders of density perturbation provide a stable description of the nonlinear galaxy system.
基金the support from the science research grants from the China Manned Space Project with NO.CMS-CSST-2021-B01supported by the World Premier International Research Center Initiative(WPI),MEXT,Japan+12 种基金the Ontario Research Fund:Research Excellence Program(ORF-RE)Natural Sciences and Engineering Research Council of Canada(NSERC)[funding reference number RGPIN-2019-067,CRD 523638-201,555585-20]Canadian Institute for Advanced Research(CIFAR)Canadian Foundation for Innovation(CFI)the National Natural Science Foundation of China(NSFC,Grant No.11929301)Simons FoundationThoth Technology IncAlexander von Humboldt Foundationthe Niagara supercomputers at the SciNet HPC Consortiumthe Canada Foundation for Innovationthe Government of OntarioOntario Research Fund—Research Excellencethe University of Toronto。
文摘We examine the possibility of applying the baryonic acoustic oscillation reconstruction method to improve the neutrino massΣm_νconstraint.Thanks to the Gaussianization of the process,we demonstrate that the reconstruction algorithm could improve the measurement accuracy by roughly a factor of two.On the other hand,the reconstruction process itself becomes a source of systematic error.While the algorithm is supposed to produce the displacement field from a density distribution,various approximations cause the reconstructed output to deviate on intermediate scales.Nevertheless,it is still possible to benefit from this Gaussianized field,given that we can carefully calibrate the“transfer function”between the reconstruction output and theoretical displacement divergence from simulations.The limitation of this approach is then set by the numerical stability of this transfer function.With an ensemble of simulations,we show that such systematic error could become comparable to statistical uncertainties for a DESI-like survey and be safely neglected for other less ambitious surveys.
基金the support of 2020SKA0110402,MOST-2018YFE0120800National Key R&D Program of China No.2022YFF0503404+5 种基金the National Natural Science Foundation of China(NSFC,Grant Nos.11822305,11773031 and 11633004)support of the National Natural Science Foundation of China(NSFC,Grant Nos.11473044 and 11973047)the Chinese Academy of Sciences grants QYZDJ-SSW-SLH017,XDB23040100,XDA15020200supported by the National Research Foundation of South Africa under Grant Nos.150580,120385 and 120378NIThe CS program“New Insights into Astrophysics and Cosmology with Theoretical Models confronting Observational Data”supported by the science research grants from the China Manned Space Project with NO.CMS-CSST-2021-B01 and CMS-CSST-2021-A01。
文摘Cross-correlating the data on neutral hydrogen(HⅠ)21 cm intensity mapping with galaxy surveys is an effective method to extract astrophysical and cosmological information.In this work,we investigate the cross-correlation of MeerKAT single-dish mode HⅠintensity mapping and China Space Station Telescope(CSST)spectroscopic galaxy surveys.We simulate a survey area of~300 deg~2 of MeerKAT and CSST surveys at z=0.5 using MultiDark N-body simulation.The PC A algorithm is applied to remove the foregrounds of HⅠintensity mapping,and signal compensation is considered to solve the signal loss problem in HⅠ-galaxy cross power spectrum caused by the foreground removal process.We find that from CSST galaxy auto and MeerKAT-CSST cross power spectra,the constraint accuracy of the parameter productΩ_(HⅠ)b_(HⅠ)r_(HⅠ,g)can reach~1%,which is about one order of magnitude higher than the current results.After performing the full MeerKAT HⅠintensity mapping survey with5000 deg~2 survey area,the accuracy can be enhanced to<0.3%.This implies that the MeerKAT-CSST cross-correlation can be a powerful tool to probe the cosmic HⅠproperty and the evolution of galaxies and the Universe.
基金financial support from the SERB,DST,Government of India through the project CRG/2019/001110IUCAA,Pune for providing support through associateship program。
文摘The holographic dark energy models provide an alternative description of dark energy.These models are motivated by the possible application of the holographic principle to the dark energy problem.In this work,we present a theoretical study of the one parameter Li holographic dark energy and the two parameter Barrow holographic dark energy models using configuration entropy of the matter distribution in the universe.The configuration entropy rate exhibits a distinct minimum at a specific scale factor that corresponds to the epoch,beyond which dark energy takes a driving role in the accelerated expansion of the universe.We find that the location of the minimum and magnitude of the entropy rate at the minimum are sensitive to the parameters of the models.We find the best fit relations between these quantities and the parameters of each model.We propose that these relations can be used to constrain the parameters of the holographic dark energy models from future observations such as the SKA.Our study suggests that the signature of a large quantum gravitational effect on the future event horizon can be detected from measurements of the configuration entropy of the matter distribution at multiple redshifts.
基金the support of NSFC-11822305, NSFC-11773031, NSFC-11633004, MOST-2018YFE0120800, MOST-2020SKA0110402, and CAS Interdisciplinary Innovation Teamsupported by the science research grants from the China Manned Space Project with NO.CMSCSST-2021-B01 and CMS-CSST-2021-A01. Z.Y.Z+1 种基金support by the National Natural Science Foundation of China (11773051 and 12022303)the CAS Pioneer Hundred Talents Program。
文摘The China Space Station Telescope(CSST) photometric survey aims to perform a high spatial resolution(~0.″ 15)photometric imaging for the targets that cover a large sky area(~17,500 deg^(2)) and wide wavelength range(from NUV to NIR). It expects to explore the properties of dark matter, dark energy, and other important cosmological and astronomical areas. In this work, we evaluate whether the filter design of the Multi-channel Imager(MCI), one of the five instruments of the CSST, can provide accurate photometric redshift(photoz) measurements with its nine medium-band filters to meet the relevant scientific objectives. We generate the mock data based on the COSMOS photometric redshift catalog with astrophysical and instrumental effects. The application of upper limit information of low signal-to-noise ratio data is adopted in the estimation of photoz. We investigate the dependency of photoz accuracy on the filter parameters, such as band position and width. We find that the current MCI filter design can achieve good photoz measurements with accuracy σ_(z)■ 0.017 and outlier fraction f_(c)■ 2.2%. It can effectively improve the photoz measurements of the main CSST survey using the Survey Camera to an accuracy σ_(z)■ 0.015 and outlier fraction f_(c)■ 1.5%. This indicates that the original MCI filters are proper for the photoz calibration.
文摘We present an analysis of the fluctuation of the local Hubble flow using 350 galaxies in the Local Volume (D 〈 5 Mpc, hereafter LV) with accurate measurements of distances, positions and radial velocities, and compare the results with the theoretical prediction of the local Hubble flow induced by density perturbations. This allows us to set a useful constraint on the local Ω parameters: ΩM - 0.6 and ΩA - 0.7, which may serve as compelling evidence for the existence of dark energy in the local Universe.
基金supported by the National Natural Science Foundation of China(Grant No.11621303)。
文摘We study the connections between the pairwise velocity moment generating function G(k_(‖),r)and redshift space distortion(RSD)modeling.Here k_(‖)is the Fourier wavevector parallel to the line of sight,and r is the pair separation vector.We demonstrate its usage by two examples.(1)Besides the known relations between G and the RSD power spectrum(and the correlation function),we propose a new RSD statistics Ps(k_(‖),r_(丄))whose connection to G is convenient to evaluate numerically.(2)We then develop a fast method to numerically evaluate G,and apply it to a high resolution N-body simulation.We find that G(ln G)shows complicated dependence on k_(‖)beyond the linear and quadratic dependencies.This not only shows inaccuracy in some existing models and identifies sources of inaccuracy but also provides possible ways of improving the RSD modeling.Consequently,more comprehensive investigations on G are needed to fully explore the usage of G in RSD modeling.
基金supported by the project“Understanding Dark Universe Using Large Scale Structure of the Universe”,funded by the Ministry of Science。
文摘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 nonGaussianity 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 theΛCDM prediction.