There continues to be good reason to believe that dark matter particles,which only"feel"the gravitational force,influence the local and distant Universe,despite drawing a complete blank in the search for suc...There continues to be good reason to believe that dark matter particles,which only"feel"the gravitational force,influence the local and distant Universe,despite drawing a complete blank in the search for such a particle.The expansion rate of the Universe is defined by the Hubble constant h.Measurements of the Hubble constant at different wavelengths produce different results,differing well beyond their errors.Here it is shown that the two precise but different values for the Hubble constant can be used to derive the mass of a weakly interacting massive particle(WIMP).An approximate mass of 1022 eV is determined with indications of why,so far,it has not been found and what is required to get positive confirmation of its presence.This result also indicates that the Hubble constant is the sum of more than one contribution with suggestions for experimental tests to determine,more precisely,the level of these contributions.展开更多
Dark energy can be studied by its influence on the expansion of the Universe.We investigate current constraints on early dark energy（EDE） achievable by the combined observational data from type Ia supernovae（557）,...Dark energy can be studied by its influence on the expansion of the Universe.We investigate current constraints on early dark energy（EDE） achievable by the combined observational data from type Ia supernovae（557）,baryon acoustic oscillations,the current cosmic microwave background and the observed Hubble pa-rameter.We find that combining these data sets provides powerful constraints on early dark energy and the best fit values of the parameters in 68% and 95% confidence-level regions are：Ωm0=0.2897 ＋0.0149＋0.0207 -0.0138-0.0194,Ωe=0.0129 ＋0.0272＋0.0381 -0.0129-0.0129,w0= -1.0415＋0.0891＋0.1182 -0.109-0.1604,and h=0.6988＋0.0059＋0.0083 -0.0058-0.0081.展开更多
We consider different observational effects to test a modified gravity approach involving the cosmological constant in the common description of dark matter and dark energy.We obtain upper limits for the cosmological ...We consider different observational effects to test a modified gravity approach involving the cosmological constant in the common description of dark matter and dark energy.We obtain upper limits for the cosmological constant by studying the scaling relations for 12 nearby galaxy clusters,the radiated power from gravitational waves and the Tully-Fisher relation for super spiral galaxies.Our estimations reveal that,for all these cases,the upper limits forΛare consistent with its actual value predicted by cosmological observations.展开更多
This work uses a combination of a variational auto-encoder and generative adversarial network to compare different dark energy models in light of observations, e.g., the distance modulus from type Ia supernovae. The n...This work uses a combination of a variational auto-encoder and generative adversarial network to compare different dark energy models in light of observations, e.g., the distance modulus from type Ia supernovae. The network finds an analytical variational approximation to the true posterior of the latent parameters in the models, yielding consistent model comparison results with those derived by the standard Bayesian method, which suffers from a computationally expensive integral over the parameters in the product of the likelihood and the prior. The parallel computational nature of the network together with the stochastic gradient descent optimization technique leads to an efficient way to compare the physical models given a set of observations. The converged network also provides interpolation for a dataset, which is useful for data reconstruction.展开更多
Physical processes involving baryons could leave a non-negligible imprint on the distribution of cosmic matter.A series of simulated data sets at high resolution with identical initial conditions are employed for coun...Physical processes involving baryons could leave a non-negligible imprint on the distribution of cosmic matter.A series of simulated data sets at high resolution with identical initial conditions are employed for count-in-cell analysis,including one N-body pure dark matter run,one with only adiabatic gas and one with dissipative processes.Variances and higher order cumulants Sn of dark matter and gas are estimated.It is found that physical processes with baryons mainly affect distributions of dark matter at scales less than 1 h-1 Mpc.In comparison with the pure dark matter run,adiabatic processes alone strengthen the variance of dark matter by～10%at a scale of 0.1 h-1 Mpc,while the Sn parameters of dark matter only mildly deviate by a few percent.The dissipative gas run does not differ much from the adiabatic run in terms of variance for dark matter,but renders significantly different Sn parameters describing the dark matter,bringing about a more than 10%enhancement to S3 at 0.1 h-1 Mpc and z=0 and being even larger at a higher redshift.Distribution patterns of gas in two hydrodynamical simulations are quite different.Variance of gas at z=0 decreases by～30%in the adiabatic simulation but by～60%in the nonadiabatic simulation at 0.1 h-1 Mpc.The attenuation is weaker at larger scales but is still obvious at～10 h-1 Mpc.Sn parameters of gas are biased upward at scales 〈～4 h-1 Mpc,and dissipative processes show an～84%promotion at z=0 to S3 at 0.1 h-1 Mpc in contrast with the～7%change in the adiabatic run.The segregation in clustering between gas and dark matter could have dramatic implications on modeling distributions of galaxies and relevant cosmological applications demanding fine details of matter distribution in a strongly nonlinear regime.展开更多
We present a novel method to reconstruct the temporal evolution of the speed of light c(z) in a flat Friedmann-Robertson-Walker(FRW) Universe using astronomical observations. After validating our pipeline with mock da...We present a novel method to reconstruct the temporal evolution of the speed of light c(z) in a flat Friedmann-Robertson-Walker(FRW) Universe using astronomical observations. After validating our pipeline with mock datasets, we apply our method to the latest baryon acoustic oscillations(BAO) and supernovae observations, and reconstruct c(z) in the redshift range of z ∈[0, 1.5]. We find no evidence of a varying speed of light, although we see some interesting features of △c(z), the fractional difference between c(z) and c0(the speed of light in the International System of Units), e.g.,△c(z)< 0 and △c(z)> 0 at 0.2≤z≤0.5 and 0.8≤z≤1.3, respectively, although the significance of these features is currently far below statistical importance.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
In the warm dark matter scenario, the Press-Schechter formalism is valid only for galaxy masses greater than the “velocity dispersion cut-off”. In this work we extend the predictions to masses below the velocity dis...In the warm dark matter scenario, the Press-Schechter formalism is valid only for galaxy masses greater than the “velocity dispersion cut-off”. In this work we extend the predictions to masses below the velocity dispersion cut-off, and thereby address the “Missing Satellites Problem” of the cold dark matter ΛCDM scenario, and the rest-frame ultra-violet luminosity cut-off required to not exceed the measured reionization optical depth. For warm dark matter we find agreement between predictions and observations of these two phenomena. As a by-product, we obtain the empirical Tully-Fisher relation from first principles.展开更多
In this paper we have searched for the existence of Lyra’s cosmology in a hybrid universe with minimal interaction between dark energy and normal matter using Bianchi-V space-time. To derive the exact solution, the a...In this paper we have searched for the existence of Lyra’s cosmology in a hybrid universe with minimal interaction between dark energy and normal matter using Bianchi-V space-time. To derive the exact solution, the average scale factor is taken as a =(t~nekt)1/m which describes the hybrid nature of the scale factor and generates a model of the transitioning universe from the early deceleration phase to the present acceleration phase. The quintessence model makes the matter content of the derived universe remarkably able to satisfy the null, dominant and strong energy condition. It has been found that the time varying displacement β(t) co-relates with the nature of cosmological constant Λ(t). We also discuss some physical and geometrical features of the universe.展开更多
Observations show that Type Ia supernovae （SNe Ia） are dimmer than ex- pected from a matter dominated Universe. It has been suggested that this observed phenomenon can also be explained using light absorption instea...Observations show that Type Ia supernovae （SNe Ia） are dimmer than ex- pected from a matter dominated Universe. It has been suggested that this observed phenomenon can also be explained using light absorption instead of dark energy. However, there is a serious degeneracy between the cosmic absorption parameter and the present matter density parameter Ωm when one tries to place constraints on the cosmic opacity using SNe Ia data. We combine the latest baryon acoustic oscillation （BAO） and Union2 SNe Ia data in order to break this degeneracy. Assuming a fiat ACDM model, we find that, although an opaque Universe is favored by SNe Ia＋BAO since the best fit value of the cosmic absorption parameter is larger than zero, fire = 1 is ruled out at the 99.7% confidence level. Thus, cosmic opacity is not sufficient to account for the present observations and dark energy or modified gravity is still re- quired.展开更多
We calculate the gravitational lensing probabilities by cold dark matter (CDM) halos with different density profiles, and compare them with current observations from the Cosmic Lens All-Sky Survey (CLASS) and the Jodr...We calculate the gravitational lensing probabilities by cold dark matter (CDM) halos with different density profiles, and compare them with current observations from the Cosmic Lens All-Sky Survey (CLASS) and the Jodrell-Bank VLA Astrometric Survey (JVAS). We find that the lensing probability is dramatically sensitive to the clumping of the dark matter, or quantitatively, the concentration parameter. We also find that our predicted lensing probabilities in most cases show inconsistency with the observations. It is argued that high lensing probability may not be an effective tool for probing the statistical properties of inner structures of dark matter halos.展开更多
Clusters of galaxies are the most massive objects in the Universe and precise knowledge of their mass structure is important to understand the history of structure formation and constrain still unknown types of dark c...Clusters of galaxies are the most massive objects in the Universe and precise knowledge of their mass structure is important to understand the history of structure formation and constrain still unknown types of dark contents of the Universe. X-ray spectroscopy of galaxy clusters provides rich information about the physical state of hot intracluster gas and the underlying potential structure. In this paper, starting from the basic description of clusters under equilibrium conditions, we review properties of clusters revealed primarily through X-ray observations considering their thermal and dynamical evolutions. The future prospects of cluster studies using upcoming X-ray missions are also mentioned.展开更多
Arising from gravitational deflections of light rays by large-scale struc- tures in the Universe, weak-lensing effects have been recognized as one of the most important probes in cosmological studies. In this paper, w...Arising from gravitational deflections of light rays by large-scale struc- tures in the Universe, weak-lensing effects have been recognized as one of the most important probes in cosmological studies. In this paper, we review the main progress in weak-lensing analyses, and discuss the challenges in future investigations aiming to understand the dark side of the Universe with unprecedented precisions.展开更多
When a satellite galaxy falls into a massive dark matter halo, it suffers from the dynamical friction force which drags it into the halo＇s center, where it finally merges with the central galaxy. The time interval be...When a satellite galaxy falls into a massive dark matter halo, it suffers from the dynamical friction force which drags it into the halo＇s center, where it finally merges with the central galaxy. The time interval between entry and merger is called the dynamical friction timescale （Tdf）. Many studies have been dedicated to deriving Tdf using analytical models or N-body simulations. These studies have obtained qualitative agreements on how Zdf depends on the orbital parameters, and the mass ratio between the satellite and the host＇s halo. However, there are still disagreements on deriving an accurate form for Tdf. We present a semi-analytical model to predict Tdf and we focus on interpreting the discrepancies among different studies. We find that the treatment of mass loss from the satellite by tidal stripping dominates the behavior of Tdf. We also identify other model parameters which affect the predicted Tdf.展开更多
We use controlled N-body simulation to investigate the dynamical processes(dynamical friction, tidal truncation, etc.) involved in the merging of small satellites into biggerhalos. We confirm the validity of some anal...We use controlled N-body simulation to investigate the dynamical processes(dynamical friction, tidal truncation, etc.) involved in the merging of small satellites into biggerhalos. We confirm the validity of some analytic formulae proposed earlier based on simplearguments. For rigid satellites represented by softened point masses, the merging time scale dependson both the orbital shape and concentration of the satellite. The dependence on orbital ellipticityis roughly a power law, as suggested by Lacey & Cole, and the dependence on satellite concentrationis similar to that proposed by White. When merging satellites are represented by non-rigid objects,Tidal effects must be considered. We found that material beyond the tidal radius are stripped off.The decrease in the satellite mass might mean an increase in the merging time scale, but in fact,the merging time is decreased, because the stripped-off material carries away a proportionatelylarger amount of of orbital energy and angular momentum.展开更多
Axion-like particles(ALPs) are a promising kind of dark matter candidate particle that are predicted to couple with photons in the presence of magnetic fields. The oscillations between photons and ALPs traveling in th...Axion-like particles(ALPs) are a promising kind of dark matter candidate particle that are predicted to couple with photons in the presence of magnetic fields. The oscillations between photons and ALPs traveling in the magnetic fields have been used to constrain ALP properties. In this work, we obtain some new constraints on the ALP mass ma and the photon-ALP coupling constant g with two different magnetic field models through TeV photons from PKS 2155–304. The first is the discrete-Φ model in which the magnetic field has the orientation angle Φ that changes discretely and randomly from one coherent domain to the next, and the second is the linearly-continuous-Φ model in which the magnetic field orientation angle Φ varies continuously across neighboring coherent domains. For the discrete-Φ model, we can obtain the best constraints on the ALP mass m1 = ma/(1 neV)= 0.1 and on the photon-ALP coupling constant g11= g/(10^-11 GeV^-1)= 5. The reasonable range of the ALP mass m1 is 0.08 ~ 0.2 when g11 = 5,and the only reasonable value of the photon-ALP coupling constant is g11 = 5 when m1 = 0.1. For the linearly-continuous-Φ model, we can obtain the best constraints on the ALP mass m1 = 0.1 and on the photon-ALP coupling constant g11 = 0.7. The reasonable range of the ALP mass m1 is 0.05 ~ 0.4 when g11= 0.7, and the reasonable range of the photon-ALP coupling constant g11 is 0.5 ~ 1 when m1 = 0.1.All of the results are consistent with the upper bound(g < 6.6 × 10^-11 GeV^-1, i.e., g11 < 6.6) set by the CAST experiment.展开更多
基金the support given by the Fred Hoyle Cosmology Club。
文摘There continues to be good reason to believe that dark matter particles,which only"feel"the gravitational force,influence the local and distant Universe,despite drawing a complete blank in the search for such a particle.The expansion rate of the Universe is defined by the Hubble constant h.Measurements of the Hubble constant at different wavelengths produce different results,differing well beyond their errors.Here it is shown that the two precise but different values for the Hubble constant can be used to derive the mass of a weakly interacting massive particle(WIMP).An approximate mass of 1022 eV is determined with indications of why,so far,it has not been found and what is required to get positive confirmation of its presence.This result also indicates that the Hubble constant is the sum of more than one contribution with suggestions for experimental tests to determine,more precisely,the level of these contributions.
文摘Dark energy can be studied by its influence on the expansion of the Universe.We investigate current constraints on early dark energy（EDE） achievable by the combined observational data from type Ia supernovae（557）,baryon acoustic oscillations,the current cosmic microwave background and the observed Hubble pa-rameter.We find that combining these data sets provides powerful constraints on early dark energy and the best fit values of the parameters in 68% and 95% confidence-level regions are：Ωm0=0.2897 ＋0.0149＋0.0207 -0.0138-0.0194,Ωe=0.0129 ＋0.0272＋0.0381 -0.0129-0.0129,w0= -1.0415＋0.0891＋0.1182 -0.109-0.1604,and h=0.6988＋0.0059＋0.0083 -0.0058-0.0081.
文摘We consider different observational effects to test a modified gravity approach involving the cosmological constant in the common description of dark matter and dark energy.We obtain upper limits for the cosmological constant by studying the scaling relations for 12 nearby galaxy clusters,the radiated power from gravitational waves and the Tully-Fisher relation for super spiral galaxies.Our estimations reveal that,for all these cases,the upper limits forΛare consistent with its actual value predicted by cosmological observations.
基金funded by the National Natural Science Foundation of China (Grant Nos. 11573006 and 11528306)the National Key R&D Program of China (2017YFA0402600)the 13th Five-year Informatization Plan of Chinese Academy of Sciences (XXH13505-04)
文摘This work uses a combination of a variational auto-encoder and generative adversarial network to compare different dark energy models in light of observations, e.g., the distance modulus from type Ia supernovae. The network finds an analytical variational approximation to the true posterior of the latent parameters in the models, yielding consistent model comparison results with those derived by the standard Bayesian method, which suffers from a computationally expensive integral over the parameters in the product of the likelihood and the prior. The parallel computational nature of the network together with the stochastic gradient descent optimization technique leads to an efficient way to compare the physical models given a set of observations. The converged network also provides interpolation for a dataset, which is useful for data reconstruction.
基金supported by the National Natural Science Foundation of China(Grant Nos.10873035 and 11133003)JP acknowledges the One-Hundred-Talent fellowship of CASthe Shanghai Supercomputer Center with support from the National High Technology Research and Development Program of China(863 project,No.2006AA01A125)
文摘Physical processes involving baryons could leave a non-negligible imprint on the distribution of cosmic matter.A series of simulated data sets at high resolution with identical initial conditions are employed for count-in-cell analysis,including one N-body pure dark matter run,one with only adiabatic gas and one with dissipative processes.Variances and higher order cumulants Sn of dark matter and gas are estimated.It is found that physical processes with baryons mainly affect distributions of dark matter at scales less than 1 h-1 Mpc.In comparison with the pure dark matter run,adiabatic processes alone strengthen the variance of dark matter by～10%at a scale of 0.1 h-1 Mpc,while the Sn parameters of dark matter only mildly deviate by a few percent.The dissipative gas run does not differ much from the adiabatic run in terms of variance for dark matter,but renders significantly different Sn parameters describing the dark matter,bringing about a more than 10%enhancement to S3 at 0.1 h-1 Mpc and z=0 and being even larger at a higher redshift.Distribution patterns of gas in two hydrodynamical simulations are quite different.Variance of gas at z=0 decreases by～30%in the adiabatic simulation but by～60%in the nonadiabatic simulation at 0.1 h-1 Mpc.The attenuation is weaker at larger scales but is still obvious at～10 h-1 Mpc.Sn parameters of gas are biased upward at scales 〈～4 h-1 Mpc,and dissipative processes show an～84%promotion at z=0 to S3 at 0.1 h-1 Mpc in contrast with the～7%change in the adiabatic run.The segregation in clustering between gas and dark matter could have dramatic implications on modeling distributions of galaxies and relevant cosmological applications demanding fine details of matter distribution in a strongly nonlinear regime.
基金supported by the National Key Basic Research and Development Program of China (2018YFA0404503)the National Basic Research Program of China (973 Program, 2015CB857004)the National Natural Science Foundation
文摘We present a novel method to reconstruct the temporal evolution of the speed of light c(z) in a flat Friedmann-Robertson-Walker(FRW) Universe using astronomical observations. After validating our pipeline with mock datasets, we apply our method to the latest baryon acoustic oscillations(BAO) and supernovae observations, and reconstruct c(z) in the redshift range of z ∈[0, 1.5]. We find no evidence of a varying speed of light, although we see some interesting features of △c(z), the fractional difference between c(z) and c0(the speed of light in the International System of Units), e.g.,△c(z)< 0 and △c(z)> 0 at 0.2≤z≤0.5 and 0.8≤z≤1.3, respectively, although the significance of these features is currently far below statistical importance.
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In the warm dark matter scenario, the Press-Schechter formalism is valid only for galaxy masses greater than the “velocity dispersion cut-off”. In this work we extend the predictions to masses below the velocity dispersion cut-off, and thereby address the “Missing Satellites Problem” of the cold dark matter ΛCDM scenario, and the rest-frame ultra-violet luminosity cut-off required to not exceed the measured reionization optical depth. For warm dark matter we find agreement between predictions and observations of these two phenomena. As a by-product, we obtain the empirical Tully-Fisher relation from first principles.
文摘利用Union2 557个Ia型超新星数据限制宇宙学参数qo、jo和so,在红移z≤1.4范围内校准5个γ暴(gamma-ray burst,GRB)光度关系.假设γ暴光度关系不随红移演化,得到66个高红移γ暴的距离模数.最后综合利用宇宙微波背景(Cosmic Microwave Background,CMB)辐射观测数据、重子声波震荡(Baryon AcousticOscillations,BAO)观测数据与116个具有红移的γ暴数据限制几个常见的暗能量模型.根据贝叶斯判据(Bayesian Information Criterion,BIC),发现ACDM模型是最好的模型;根据Akaike判据(Akaike Information Criterion,AIC),发现JBP模型是最好的模型.
文摘In this paper we have searched for the existence of Lyra’s cosmology in a hybrid universe with minimal interaction between dark energy and normal matter using Bianchi-V space-time. To derive the exact solution, the average scale factor is taken as a =(t~nekt)1/m which describes the hybrid nature of the scale factor and generates a model of the transitioning universe from the early deceleration phase to the present acceleration phase. The quintessence model makes the matter content of the derived universe remarkably able to satisfy the null, dominant and strong energy condition. It has been found that the time varying displacement β(t) co-relates with the nature of cosmological constant Λ(t). We also discuss some physical and geometrical features of the universe.
基金supported by the National Natural Science Foundation of China(Grant Nos. 10935013, 11175093, 11222545 and 11075083)Zhejiang Provincial Natural Science Foundation of China (Grant Nos. Z6100077 and R6110518)+6 种基金the Foundation for the Author of National Excellent Doctoral Dissertation of PR China (FANEDD, Grant No. 200922)the National Basic Research Program of China (973 program, Grant No. 2010CB832803)the Program for New Century Excellent Talents in University (NCET, Grant No. 09-0144)the Program for Changjiang Scholars and Innovative Research Team in University (PCSIRT, Grant No. IRT0964)Hunan Provincial Natural Science Foundation of China (Grant No. 11JJ7001)the Specialized Research Fund for the Doctoral Program of Higher Education (SRFDP, Grant No. 20124306110001)the Program for the Key Discipline in Hunan Province
文摘Observations show that Type Ia supernovae （SNe Ia） are dimmer than ex- pected from a matter dominated Universe. It has been suggested that this observed phenomenon can also be explained using light absorption instead of dark energy. However, there is a serious degeneracy between the cosmic absorption parameter and the present matter density parameter Ωm when one tries to place constraints on the cosmic opacity using SNe Ia data. We combine the latest baryon acoustic oscillation （BAO） and Union2 SNe Ia data in order to break this degeneracy. Assuming a fiat ACDM model, we find that, although an opaque Universe is favored by SNe Ia＋BAO since the best fit value of the cosmic absorption parameter is larger than zero, fire = 1 is ruled out at the 99.7% confidence level. Thus, cosmic opacity is not sufficient to account for the present observations and dark energy or modified gravity is still re- quired.
基金This work was partially supported by the National Natural Science Foundation of China under Grant No. 10003002.
文摘We calculate the gravitational lensing probabilities by cold dark matter (CDM) halos with different density profiles, and compare them with current observations from the Cosmic Lens All-Sky Survey (CLASS) and the Jodrell-Bank VLA Astrometric Survey (JVAS). We find that the lensing probability is dramatically sensitive to the clumping of the dark matter, or quantitatively, the concentration parameter. We also find that our predicted lensing probabilities in most cases show inconsistency with the observations. It is argued that high lensing probability may not be an effective tool for probing the statistical properties of inner structures of dark matter halos.
文摘Clusters of galaxies are the most massive objects in the Universe and precise knowledge of their mass structure is important to understand the history of structure formation and constrain still unknown types of dark contents of the Universe. X-ray spectroscopy of galaxy clusters provides rich information about the physical state of hot intracluster gas and the underlying potential structure. In this paper, starting from the basic description of clusters under equilibrium conditions, we review properties of clusters revealed primarily through X-ray observations considering their thermal and dynamical evolutions. The future prospects of cluster studies using upcoming X-ray missions are also mentioned.
基金Supported by the National Natural Science Foundation of China
文摘Arising from gravitational deflections of light rays by large-scale struc- tures in the Universe, weak-lensing effects have been recognized as one of the most important probes in cosmological studies. In this paper, we review the main progress in weak-lensing analyses, and discuss the challenges in future investigations aiming to understand the dark side of the Universe with unprecedented precisions.
基金funded by the National Natural Science Foundation of China (Grant No. 10573028)the Key Project (Grant No. 10833005)+4 种基金the Group Innovation Project (Grant No. 10821302)the National Basic Research Program of China (973 ProgramNo. 2007CB815402)supported by the One Hundred Talents Project of the Chinese Academy of Sciencesthe foundation for the authors of CAS excellent doctoral dissertations
文摘When a satellite galaxy falls into a massive dark matter halo, it suffers from the dynamical friction force which drags it into the halo＇s center, where it finally merges with the central galaxy. The time interval between entry and merger is called the dynamical friction timescale （Tdf）. Many studies have been dedicated to deriving Tdf using analytical models or N-body simulations. These studies have obtained qualitative agreements on how Zdf depends on the orbital parameters, and the mass ratio between the satellite and the host＇s halo. However, there are still disagreements on deriving an accurate form for Tdf. We present a semi-analytical model to predict Tdf and we focus on interpreting the discrepancies among different studies. We find that the treatment of mass loss from the satellite by tidal stripping dominates the behavior of Tdf. We also identify other model parameters which affect the predicted Tdf.
基金Supported by the National Natural Science Foundation of China
文摘We use controlled N-body simulation to investigate the dynamical processes(dynamical friction, tidal truncation, etc.) involved in the merging of small satellites into biggerhalos. We confirm the validity of some analytic formulae proposed earlier based on simplearguments. For rigid satellites represented by softened point masses, the merging time scale dependson both the orbital shape and concentration of the satellite. The dependence on orbital ellipticityis roughly a power law, as suggested by Lacey & Cole, and the dependence on satellite concentrationis similar to that proposed by White. When merging satellites are represented by non-rigid objects,Tidal effects must be considered. We found that material beyond the tidal radius are stripped off.The decrease in the satellite mass might mean an increase in the merging time scale, but in fact,the merging time is decreased, because the stripped-off material carries away a proportionatelylarger amount of of orbital energy and angular momentum.
文摘Axion-like particles(ALPs) are a promising kind of dark matter candidate particle that are predicted to couple with photons in the presence of magnetic fields. The oscillations between photons and ALPs traveling in the magnetic fields have been used to constrain ALP properties. In this work, we obtain some new constraints on the ALP mass ma and the photon-ALP coupling constant g with two different magnetic field models through TeV photons from PKS 2155–304. The first is the discrete-Φ model in which the magnetic field has the orientation angle Φ that changes discretely and randomly from one coherent domain to the next, and the second is the linearly-continuous-Φ model in which the magnetic field orientation angle Φ varies continuously across neighboring coherent domains. For the discrete-Φ model, we can obtain the best constraints on the ALP mass m1 = ma/(1 neV)= 0.1 and on the photon-ALP coupling constant g11= g/(10^-11 GeV^-1)= 5. The reasonable range of the ALP mass m1 is 0.08 ~ 0.2 when g11 = 5,and the only reasonable value of the photon-ALP coupling constant is g11 = 5 when m1 = 0.1. For the linearly-continuous-Φ model, we can obtain the best constraints on the ALP mass m1 = 0.1 and on the photon-ALP coupling constant g11 = 0.7. The reasonable range of the ALP mass m1 is 0.05 ~ 0.4 when g11= 0.7, and the reasonable range of the photon-ALP coupling constant g11 is 0.5 ~ 1 when m1 = 0.1.All of the results are consistent with the upper bound(g < 6.6 × 10^-11 GeV^-1, i.e., g11 < 6.6) set by the CAST experiment.
