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
We revisit the epoch of cosmic speed-up characterized by the redshift of transition from a decelerated to an accelerated phase.This redshift is termed the transition redshift(z_(t)).We use the spatially flat and non-f...We revisit the epoch of cosmic speed-up characterized by the redshift of transition from a decelerated to an accelerated phase.This redshift is termed the transition redshift(z_(t)).We use the spatially flat and non-flat variants of the most commonΛCDM and XCDM models to put constraints on the transition redshift along with the other model parameters.The data for this analysis come from the recent and updated Pantheon+supernova(SN)data set and the Hubble parameter measurements obtained from Cosmic Chronometers.We consider both data sets with their respective covariance matrices incorporating all statistical and systematic uncertainties.We observe that using the combined data sets of H(z)and SNe,the best fit value of transition redshift lies in the range 0.61<z_(t)<0.79 for all four dark energy models.Incidentally,we observe a positive curvature for the non-flat models,correlations between several model parameters and a strong degeneracy between the curvature and the equation of state parameter.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
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.
文摘We revisit the epoch of cosmic speed-up characterized by the redshift of transition from a decelerated to an accelerated phase.This redshift is termed the transition redshift(z_(t)).We use the spatially flat and non-flat variants of the most commonΛCDM and XCDM models to put constraints on the transition redshift along with the other model parameters.The data for this analysis come from the recent and updated Pantheon+supernova(SN)data set and the Hubble parameter measurements obtained from Cosmic Chronometers.We consider both data sets with their respective covariance matrices incorporating all statistical and systematic uncertainties.We observe that using the combined data sets of H(z)and SNe,the best fit value of transition redshift lies in the range 0.61<z_(t)<0.79 for all four dark energy models.Incidentally,we observe a positive curvature for the non-flat models,correlations between several model parameters and a strong degeneracy between the curvature and the equation of state parameter.
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.
