In this paper, we utilize recent observational data from gamma-ray bursts(GRBs) and Pantheon+ supernovae Ia(SNe Ia) samples to explore the interacting dark energy(IDE) model in a phenomenological scenario. Results fro...In this paper, we utilize recent observational data from gamma-ray bursts(GRBs) and Pantheon+ supernovae Ia(SNe Ia) samples to explore the interacting dark energy(IDE) model in a phenomenological scenario. Results from GRBs alone, SNe Ia and GRBs+SNe Ia indicate that the energy is transferred from dark energy to dark matter and the coincidence problem is alleviated. The value of H0from GRBs+SNe Ia in the IDE scenario shows agreement with the SH0ES measurement. Considering the age estimate of the quasar APM 08279+5255 at z = 3.91, we find that the phenomenological IDE scenario can predict a cosmic age greater than that of the ΛCDM model, thus the cosmic age problem can be alleviated.展开更多
It was hypothesized in the literature that some physical parameters may be time-evolving and the astrophysical data can serve as a probe.Recently,the James Webb Space Telescope(JWST)released its early observations.In ...It was hypothesized in the literature that some physical parameters may be time-evolving and the astrophysical data can serve as a probe.Recently,the James Webb Space Telescope(JWST)released its early observations.In this work,we select the JWST spectroscopic observations of the high redshift(z>7.1)galaxies with strong[O III](λ=4959?and 5007?in the rest frame)emission lines to constraint the evolution of the fine structure constant(α).With the spectra from two galaxies at redshifts of 7.19 and 8.47,the deviation ofαfrom its fiducial value is found to be as small as 0.44_(-8.3-1.7)^(8.4+1.7)×10^(-4)and-10.0_(-18-1.5)^(+18+1.5)×10^(-4)respectively(the first error is statistical and the latter is systematic).The combination of our results with the previous data reveals that 1/αdα/dt=0.30_(-4.5)^(+4.5)×10^(-17)yr^(-1).Clearly,there is no evidence for a cosmic evolution ofα.The prospect of further constraining the time evolution ofαis also discussed.The scalar field of dark energy is hypothesized to drive the acceleration of the universe’s expansion through an interaction with the electromagnetic field.By integrating the observational data of the fine-structure constant variation,△α/α(z),we have established a stringent upper limit on the coupling strength between dark energy and electromagnetism.Our analysis yieldsζ≤3.92×10^(-7)at the 95%confidence level,representing the most stringent bound to date.展开更多
A great challenge for 21 cm intensity mapping experiments is the strong foreground radiation which is orders of magnitude brighter than the 21 cm signal.Removal of the foreground takes advantage of the fact that its f...A great challenge for 21 cm intensity mapping experiments is the strong foreground radiation which is orders of magnitude brighter than the 21 cm signal.Removal of the foreground takes advantage of the fact that its frequency spectrum is smooth while the redshifted 21 cm signal spectrum is stochastic.However,a complication is the nonsmoothness of the instrument response.This paper describes the electromagnetic simulation of the Tianlai cylinder array,a pathfinder for 21 cm intensity mapping experiments.Due to the vast scales involved,a direct simulation requires a large amount of computing resources.We have made the simulation practical by using a combination of methods:first simulate a single feed,then an array of feed units,finally with the feed array and a cylindrical reflector together,obtain the response for a single cylinder.We studied its radiation pattern,bandpass response and the effects of mutual coupling between feed units,and compared the results with observation.Many features seen in the measurement result are reproduced well in the simulation,especially the oscillatory features which are associated with the standing waves on the reflector.The mutual coupling between feed units is quantified with Sparameters,which decrease as the distance between the two feeds increases.Based on the simulated S-parameters,we estimate the correlated noise which has been seen in the visibility data,and the results show very good agreement with the data in both magnitude and frequency structures.These results provide useful insights on the problem of 21 cm signal extraction for real instruments.展开更多
We have investigated late time acceleration for a spatially fiat dust filled Universe in Brans- Dicke theory in the presence of a positive cosmological constant A. Expressions for Hubble＇s constant, luminosity distan...We have investigated late time acceleration for a spatially fiat dust filled Universe in Brans- Dicke theory in the presence of a positive cosmological constant A. Expressions for Hubble＇s constant, luminosity distance and apparent magnitude have been obtained for our model. The theoretical results are compared with observed values of the latest 287 high redshift （0.3 ≤ z ≤1.4） Type Ia supernova data taken from the Union 2.1 compilation to estimate present values of matter and dark energy parame- ters, （Ωm）0 and （ΩA）0. We have also estimated the present value of Hubble＇s constant H0 in light of an updated sample of Hubble parameter measurements including 19 independent data points. The results are found to be in good agreement with recent astrophysical observations. We also calculated various physical parameters such as matter and dark energy densities, present age of the Universe and decelera- tion parameter. The value for Brans-Dicke-coupling constant ω is set to be 40 000 based on accuracy of solar system tests and recent experimental evidence.展开更多
We build a sample of 298 spectroscopically-confirmed galaxies at redshift z - 2, selected in the z850-band from the GOODS-MUSIC catalog. By utilizing the rest frame 8 p.m luminosity as a proxy of the star formation ra...We build a sample of 298 spectroscopically-confirmed galaxies at redshift z - 2, selected in the z850-band from the GOODS-MUSIC catalog. By utilizing the rest frame 8 p.m luminosity as a proxy of the star formation rate （SFR）, we check the accuracy of the standard SED-fitting technique, finding it is not accurate enough to provide reliable estimates of the physical parameters of galaxies. We then develop a new SED-fitting method that includes the IR luminosity as a prior and a generalized Calzetti law with a variable Rv. Then we exploit the new method to re-analyze our galaxy sample, and to robustly determine SFRs, stellar masses and ages. We find that there is a general trend of increasing attenuation with the SFR. Moreover, we find that the SFRs range between a few to 103 M~ yr-1, the masses from 109 to 4 ~ 1011 Mo, and the ages from a few tens of Myr to more than 1 Gyr. We discuss how individual age measurements of highly attenuated objects indicate that dust must have formed within a few tens of Myr and already been copious at 〈 100 Myr. In addition, we find that low luminosity galaxies harbor, on average, significantly older stellar populations and are also less massive than brighter ones; we discuss how these findings and the well known ＇downsizing＇ scenario are consistent in a framework where less massive galaxies form first, but their star formation lasts longer. Finally, we find that the near-IR attenuation is not scarce for luminous objects, contrary to what is customarily assumed; we discuss how this affects the interpretation of the observed M,/L ratios.展开更多
基金supported by the Guizhou Provincial Science and Technology Foundations (QKHJC-ZK[2021] Key 020 and QKHJC-ZK [2024] general 443)。
文摘In this paper, we utilize recent observational data from gamma-ray bursts(GRBs) and Pantheon+ supernovae Ia(SNe Ia) samples to explore the interacting dark energy(IDE) model in a phenomenological scenario. Results from GRBs alone, SNe Ia and GRBs+SNe Ia indicate that the energy is transferred from dark energy to dark matter and the coincidence problem is alleviated. The value of H0from GRBs+SNe Ia in the IDE scenario shows agreement with the SH0ES measurement. Considering the age estimate of the quasar APM 08279+5255 at z = 3.91, we find that the phenomenological IDE scenario can predict a cosmic age greater than that of the ΛCDM model, thus the cosmic age problem can be alleviated.
基金the National Natural Science Foundation of China(NSFC,Grant Nos.11921003,12233011,and 12373002)。
文摘It was hypothesized in the literature that some physical parameters may be time-evolving and the astrophysical data can serve as a probe.Recently,the James Webb Space Telescope(JWST)released its early observations.In this work,we select the JWST spectroscopic observations of the high redshift(z>7.1)galaxies with strong[O III](λ=4959?and 5007?in the rest frame)emission lines to constraint the evolution of the fine structure constant(α).With the spectra from two galaxies at redshifts of 7.19 and 8.47,the deviation ofαfrom its fiducial value is found to be as small as 0.44_(-8.3-1.7)^(8.4+1.7)×10^(-4)and-10.0_(-18-1.5)^(+18+1.5)×10^(-4)respectively(the first error is statistical and the latter is systematic).The combination of our results with the previous data reveals that 1/αdα/dt=0.30_(-4.5)^(+4.5)×10^(-17)yr^(-1).Clearly,there is no evidence for a cosmic evolution ofα.The prospect of further constraining the time evolution ofαis also discussed.The scalar field of dark energy is hypothesized to drive the acceleration of the universe’s expansion through an interaction with the electromagnetic field.By integrating the observational data of the fine-structure constant variation,△α/α(z),we have established a stringent upper limit on the coupling strength between dark energy and electromagnetism.Our analysis yieldsζ≤3.92×10^(-7)at the 95%confidence level,representing the most stringent bound to date.
基金supported by the Ministry of Science and Technology(MOST)-BRICS Flagship Project 2018YFE0120800National SKA Program of China No.2020SKA0110401+6 种基金the National Key R&D Program 2017YFA0402603the National Natural Science Foundation of China(NSFC,Grant Nos.11973047,11633004 and U1631118)the Chinese Academy of Sciences(CAS)Strategic Priority Research Program XDA15020200the CAS Frontier Science Key Project QYZDJ–SSW–SLH017the CAS Inter-disciplinary Innovation Team(JCTD-2019-05)the CAS Key Instruments project ZDKYYQ20200008the Hebei Key Laboratory of Radio Astronomy Technology(HKLRAT)。
文摘A great challenge for 21 cm intensity mapping experiments is the strong foreground radiation which is orders of magnitude brighter than the 21 cm signal.Removal of the foreground takes advantage of the fact that its frequency spectrum is smooth while the redshifted 21 cm signal spectrum is stochastic.However,a complication is the nonsmoothness of the instrument response.This paper describes the electromagnetic simulation of the Tianlai cylinder array,a pathfinder for 21 cm intensity mapping experiments.Due to the vast scales involved,a direct simulation requires a large amount of computing resources.We have made the simulation practical by using a combination of methods:first simulate a single feed,then an array of feed units,finally with the feed array and a cylindrical reflector together,obtain the response for a single cylinder.We studied its radiation pattern,bandpass response and the effects of mutual coupling between feed units,and compared the results with observation.Many features seen in the measurement result are reproduced well in the simulation,especially the oscillatory features which are associated with the standing waves on the reflector.The mutual coupling between feed units is quantified with Sparameters,which decrease as the distance between the two feeds increases.Based on the simulated S-parameters,we estimate the correlated noise which has been seen in the visibility data,and the results show very good agreement with the data in both magnitude and frequency structures.These results provide useful insights on the problem of 21 cm signal extraction for real instruments.
基金supported by the CGCOST Research Project 789/CGCOST/MRP/14
文摘We have investigated late time acceleration for a spatially fiat dust filled Universe in Brans- Dicke theory in the presence of a positive cosmological constant A. Expressions for Hubble＇s constant, luminosity distance and apparent magnitude have been obtained for our model. The theoretical results are compared with observed values of the latest 287 high redshift （0.3 ≤ z ≤1.4） Type Ia supernova data taken from the Union 2.1 compilation to estimate present values of matter and dark energy parame- ters, （Ωm）0 and （ΩA）0. We have also estimated the present value of Hubble＇s constant H0 in light of an updated sample of Hubble parameter measurements including 19 independent data points. The results are found to be in good agreement with recent astrophysical observations. We also calculated various physical parameters such as matter and dark energy densities, present age of the Universe and decelera- tion parameter. The value for Brans-Dicke-coupling constant ω is set to be 40 000 based on accuracy of solar system tests and recent experimental evidence.
基金Supported by the National Natural Science Foundation of China
文摘We build a sample of 298 spectroscopically-confirmed galaxies at redshift z - 2, selected in the z850-band from the GOODS-MUSIC catalog. By utilizing the rest frame 8 p.m luminosity as a proxy of the star formation rate （SFR）, we check the accuracy of the standard SED-fitting technique, finding it is not accurate enough to provide reliable estimates of the physical parameters of galaxies. We then develop a new SED-fitting method that includes the IR luminosity as a prior and a generalized Calzetti law with a variable Rv. Then we exploit the new method to re-analyze our galaxy sample, and to robustly determine SFRs, stellar masses and ages. We find that there is a general trend of increasing attenuation with the SFR. Moreover, we find that the SFRs range between a few to 103 M~ yr-1, the masses from 109 to 4 ~ 1011 Mo, and the ages from a few tens of Myr to more than 1 Gyr. We discuss how individual age measurements of highly attenuated objects indicate that dust must have formed within a few tens of Myr and already been copious at 〈 100 Myr. In addition, we find that low luminosity galaxies harbor, on average, significantly older stellar populations and are also less massive than brighter ones; we discuss how these findings and the well known ＇downsizing＇ scenario are consistent in a framework where less massive galaxies form first, but their star formation lasts longer. Finally, we find that the near-IR attenuation is not scarce for luminous objects, contrary to what is customarily assumed; we discuss how this affects the interpretation of the observed M,/L ratios.
