In this work,we investigate a joint fitting approach based on theoretical models of power spectra associated with density-field reconstruction.Specifically,we consider the matter auto-power spectra before and after ba...In this work,we investigate a joint fitting approach based on theoretical models of power spectra associated with density-field reconstruction.Specifically,we consider the matter auto-power spectra before and after baryon acoustic oscillations(BAO)reconstruction,as well as the cross-power spectrum between the pre-and post-reconstructed density fields.We present redshift-space models for these three power spectra at the one-loop level within the framework of standard perturbation theory,and perform a joint analysis using three types of power spectra,and quantify their impact on parameter constraints.When restricting the analysis to wavenumbers k≤0.2 h Mpc^(−1)and adopting a smoothing scale of R_(s)=15 h^(−1)Mpc,we find that incorporating all three power spectra improves parameter constraints by approximately 11%–16%compared to using only the post-reconstruction power spectrum,with the Figure of Merit increasing by 10.5%.These results highlight the advantages of leveraging multiple power spectra in BAO reconstruction,ultimately enabling more precise cosmological parameter estimation.展开更多
In observational cosmology,a supernova la is used as a standard candle in order to extend the Hubble diagram to a higher redshift range.Astrophysicists found that the observed brightness of high redshift supernovae la...In observational cosmology,a supernova la is used as a standard candle in order to extend the Hubble diagram to a higher redshift range.Astrophysicists found that the observed brightness of high redshift supernovae la is dimmer than expected.This dimming effect is considered observational evidence for the existence of dark energy in the universe.It should be noted that this conclusion is based on an assumption that the mass density of the cosmic plasma is very small.Therefore,the dimming effect caused by the Compton scattering of free electrons in cosmic plasma can be neglected.X-ray observations suggest that the mass density of the cosmic plasma may be very large.In theory,the observed dimming effect of high redshift supernovae Ia may be caused by the Compton scattering of free electrons in the cosmic plasma.In this paper it will be shown that this idea is reasonable.Therefore,there is no need to introduce the confusing concept of dark energy into cosmology.展开更多
This study presents results on detecting neutral atomic hydrogen(H I)21 cm absorption in the spectrum of PKS PKS1413+13 at redshift z=0.24670041.The observation was conducted by FAST,with a spectral resolution of10 Hz...This study presents results on detecting neutral atomic hydrogen(H I)21 cm absorption in the spectrum of PKS PKS1413+13 at redshift z=0.24670041.The observation was conducted by FAST,with a spectral resolution of10 Hz,using 10 minutes of observing time.The global spectral profile is examined by modeling the absorption line using a single Gaussian function with a resolution of 10 kHz within a 2 MHz bandwidth.The goal is to determine the rate of the latest cosmic acceleration by directly measuring the redshift evolution of the H I 21 cm absorption line with Hubble flow toward a common background quasar over a decade or longer time span.This will serve as a detectable signal generated by the accelerated expansion of the Universe at redshift z<1,referred to as redshift drift z(5)or the SL effect.The measured H I gas column density in this DLA system is approximately equivalent to the initial observation value,considering uncertainties of the spin temperature of a spiral host galaxy.The high signal-to-noise ratio of 57,obtained at a 10 kHz resolution,strongly supports the feasibility of using the H I 21 cm absorption line in DLA systems to accurately measure the redshift drift rate at a precision level of around 10~(-10)per decade.展开更多
The f(R)modified gravity theory can explain the accelerating expansion of the late Universe without introducing dark energy.In this study,we predict the constraint strength on the f(R)theory using the mock data genera...The f(R)modified gravity theory can explain the accelerating expansion of the late Universe without introducing dark energy.In this study,we predict the constraint strength on the f(R)theory using the mock data generated from the Chinese Space Station Telescope(CSST)Ultra-Deep Field Type Ia supernova(SN Ia)survey and wide-field slitless spectroscopic baryon acoustic oscillation(BAO)survey.We explore three popular f(R)models and introduce a parameter b to characterize the deviation of the f(R)theory from theΛCDM theory.The Markov Chain Monte Carlo method is employed to constrain the parameters in the f(R)models,and the nuisance parameters and systematic uncertainties are also considered in the model fitting process.Besides,we also perform model comparisons between the f(R)models and theΛCDM model.We find that the constraint accuracy using the CSST SN Ia+BAO data set alone is comparable to or even better than the result given by the combination of the current relevant observations,and the CSST SN Ia+BAO survey can distinguish the f(R)models from theΛCDM model.This indicates that the CSST SN Ia and BAO surveys can effectively constrain and test the f(R)theory.展开更多
The baryon acoustic oscillations (BAO) reconstruction plays a crucial role in cosmological analysis for spectroscopic galaxy surveys because it can make the density field effectively more linear and more Gaussian.The ...The baryon acoustic oscillations (BAO) reconstruction plays a crucial role in cosmological analysis for spectroscopic galaxy surveys because it can make the density field effectively more linear and more Gaussian.The combination of the power spectra before and after the BAO reconstruction helps break degeneracies among parameters,then improves the constraints on cosmological parameters.It is therefore important to estimate the covariance matrix between pre-and post-reconstructed power spectra.In this work,we use perturbation theory to estimate the covariance matrix of the related power spectra multipoles,and check the accuracy of the derived covariance model using a large suite of dark matter halo catalogs at z=0.5.We find that the diagonal part of the auto covariance is well described by the Gaussian prediction,while the cross covariance deviates from the Gaussian prediction quickly when k>0.1 h Mpc^(-1).Additionally,we find the non-Gaussian effect in the nondiagonal part of the cross covariance is comparable to,or even stronger than,the pre-reconstruction covariance.By adding the non-Gaussian contribution,we obtain good agreement between analytical and numerical covariance matrices in the non-diagonal part up to k■0.15 h Mpc^(-1).The agreement in the diagonal part is also improved,bu still under-predicts the correlation in the cross covariance block.展开更多
基金supported by the National Natural Science Foundation of China(NSFC,Grant No.12525301)supported by the Science and Technology Facilities Council(STFC)under Grant ST/W001225/1+6 种基金supported by JSPS KAKENHI grant Nos.JP22H00130 and JP20H05855further acknowledges support form the National Key R&D Program of China No.(2022YFF0503404,2023YFA1607800,2023YFA1607803)the National Natural Science Foundation of China(NSFC,Grant Nos.12273048 and 12422301)the CAS Project for Young Scientists in Basic Research(No.YSBR-092)support from the CAS Project for Young Scientists in Basic Research(No.YSBR092)the China Manned Space Projectthe New Cornerstone Science Foundation through the XPLORER Prize.
文摘In this work,we investigate a joint fitting approach based on theoretical models of power spectra associated with density-field reconstruction.Specifically,we consider the matter auto-power spectra before and after baryon acoustic oscillations(BAO)reconstruction,as well as the cross-power spectrum between the pre-and post-reconstructed density fields.We present redshift-space models for these three power spectra at the one-loop level within the framework of standard perturbation theory,and perform a joint analysis using three types of power spectra,and quantify their impact on parameter constraints.When restricting the analysis to wavenumbers k≤0.2 h Mpc^(−1)and adopting a smoothing scale of R_(s)=15 h^(−1)Mpc,we find that incorporating all three power spectra improves parameter constraints by approximately 11%–16%compared to using only the post-reconstruction power spectrum,with the Figure of Merit increasing by 10.5%.These results highlight the advantages of leveraging multiple power spectra in BAO reconstruction,ultimately enabling more precise cosmological parameter estimation.
文摘In observational cosmology,a supernova la is used as a standard candle in order to extend the Hubble diagram to a higher redshift range.Astrophysicists found that the observed brightness of high redshift supernovae la is dimmer than expected.This dimming effect is considered observational evidence for the existence of dark energy in the universe.It should be noted that this conclusion is based on an assumption that the mass density of the cosmic plasma is very small.Therefore,the dimming effect caused by the Compton scattering of free electrons in cosmic plasma can be neglected.X-ray observations suggest that the mass density of the cosmic plasma may be very large.In theory,the observed dimming effect of high redshift supernovae Ia may be caused by the Compton scattering of free electrons in the cosmic plasma.In this paper it will be shown that this idea is reasonable.Therefore,there is no need to introduce the confusing concept of dark energy into cosmology.
基金supported by the National SKA Program of China(2022SKA0110202)the National Natural Science Foundation of China(grants No.11929301)。
文摘This study presents results on detecting neutral atomic hydrogen(H I)21 cm absorption in the spectrum of PKS PKS1413+13 at redshift z=0.24670041.The observation was conducted by FAST,with a spectral resolution of10 Hz,using 10 minutes of observing time.The global spectral profile is examined by modeling the absorption line using a single Gaussian function with a resolution of 10 kHz within a 2 MHz bandwidth.The goal is to determine the rate of the latest cosmic acceleration by directly measuring the redshift evolution of the H I 21 cm absorption line with Hubble flow toward a common background quasar over a decade or longer time span.This will serve as a detectable signal generated by the accelerated expansion of the Universe at redshift z<1,referred to as redshift drift z(5)or the SL effect.The measured H I gas column density in this DLA system is approximately equivalent to the initial observation value,considering uncertainties of the spin temperature of a spiral host galaxy.The high signal-to-noise ratio of 57,obtained at a 10 kHz resolution,strongly supports the feasibility of using the H I 21 cm absorption line in DLA systems to accurately measure the redshift drift rate at a precision level of around 10~(-10)per decade.
基金support from the National Key R&D Program of China grant Nos.2022YFF0503404,2020SKA0110402the CAS Project for Young Scientists in Basic Research(No.YSBR092)+2 种基金the support of the National Natural Science Foundation of China(NSFC,grant Nos.11473044 and 11973047)the Chinese Academy of Science grants ZDKYYQ20200008,QYZDJ-SSW-SLH017,XDB 23040100,and XDA15020200supported by science research grants from the China Manned Space Project with grant Nos.CMS-CSST-2021-B01 and CMS-CSST-2021-A01。
文摘The f(R)modified gravity theory can explain the accelerating expansion of the late Universe without introducing dark energy.In this study,we predict the constraint strength on the f(R)theory using the mock data generated from the Chinese Space Station Telescope(CSST)Ultra-Deep Field Type Ia supernova(SN Ia)survey and wide-field slitless spectroscopic baryon acoustic oscillation(BAO)survey.We explore three popular f(R)models and introduce a parameter b to characterize the deviation of the f(R)theory from theΛCDM theory.The Markov Chain Monte Carlo method is employed to constrain the parameters in the f(R)models,and the nuisance parameters and systematic uncertainties are also considered in the model fitting process.Besides,we also perform model comparisons between the f(R)models and theΛCDM model.We find that the constraint accuracy using the CSST SN Ia+BAO data set alone is comparable to or even better than the result given by the combination of the current relevant observations,and the CSST SN Ia+BAO survey can distinguish the f(R)models from theΛCDM model.This indicates that the CSST SN Ia and BAO surveys can effectively constrain and test the f(R)theory.
基金supported by National Key R&D Program of China No.2023YFA1607803National Natural Science Foundation of China (NSFC,grant No.11925303)+9 种基金by the CAS Project for Young Scientists in Basic Research (No.YSBR-092)supported by the Chinese Scholarship Council (CSC) and the University of Portsmouthsupported by the STFC grant ST/W001225/1.Y.W.supported by National Natural Science Foundation of China (NSFC,grant Nos.12273048 and 12422301)by National Key R&D Program of China No.2022YFF0503404by the Youth Innovation Promotion Association CASby the Nebula Talents Program of NAOC.G.B.Z.supported by science research grants from the China Manned Space Project with No.CMS-CSST-2021-B01the New Cornerstone Science Foundation through the XPLORER prizesupported by the ICG,SEPNet and the University of Portsmouth。
文摘The baryon acoustic oscillations (BAO) reconstruction plays a crucial role in cosmological analysis for spectroscopic galaxy surveys because it can make the density field effectively more linear and more Gaussian.The combination of the power spectra before and after the BAO reconstruction helps break degeneracies among parameters,then improves the constraints on cosmological parameters.It is therefore important to estimate the covariance matrix between pre-and post-reconstructed power spectra.In this work,we use perturbation theory to estimate the covariance matrix of the related power spectra multipoles,and check the accuracy of the derived covariance model using a large suite of dark matter halo catalogs at z=0.5.We find that the diagonal part of the auto covariance is well described by the Gaussian prediction,while the cross covariance deviates from the Gaussian prediction quickly when k>0.1 h Mpc^(-1).Additionally,we find the non-Gaussian effect in the nondiagonal part of the cross covariance is comparable to,or even stronger than,the pre-reconstruction covariance.By adding the non-Gaussian contribution,we obtain good agreement between analytical and numerical covariance matrices in the non-diagonal part up to k■0.15 h Mpc^(-1).The agreement in the diagonal part is also improved,bu still under-predicts the correlation in the cross covariance block.
