Much of the research in supernova cosmology is based on an assumption that the peak luminosity of type Ia supernovae(SNe Ia),after a standardization process,is independent of the galactic environment.A series of recen...Much of the research in supernova cosmology is based on an assumption that the peak luminosity of type Ia supernovae(SNe Ia),after a standardization process,is independent of the galactic environment.A series of recent studies suggested that there is a significant correlation between the standardized luminosity and the progenitor age of SNe Ia.The correlation found in the most recent work by Lee et al.[Mon.Not.R.Astron.Soc.517,2697(2022)]is strong enough to explain the extra dimming of distant SNe Ia and therefore casts doubts on the direct evidence of cosmic acceleration.The present work incorporates the uncertainties of progenitor ages,which were ignored in Lee et al.,into a fully Bayesian inference framework.We find a weaker dependence of supernova standardized luminosity on the progenitor age,but the detection of correlation remains significant(3.5σ).Assuming that such correlation can be extended to high redshift and applying it to the Pantheon SN Ia data set,we confirm that when the Hubble residual does not include intrinsic scatter,the age-bias could be the primary cause of the observed extra dimming of distant SNe Ia.Furthermore,we use the PAge formalism,which is a good approximation to many dark energy and modified gravity models,to do a model comparison.We find that if intrinsic scatter is included in the Hubble residual,the Lambda cold dark matter model remains a good fit.However,in a scenario without intrinsic scatter,the Lambda cold dark matter model faces a challenge.展开更多
The community assembly rules and species coexistence have always been interested by ecologists. The community phylogenetic structure is the consequence of the interaction process between the organisms and the abiotic ...The community assembly rules and species coexistence have always been interested by ecologists. The community phylogenetic structure is the consequence of the interaction process between the organisms and the abiotic environment and has been used to explain the relative impact of abiotic and biotic factors on species co-existence. In recent years, grassland degradation and biodiversity loss have become increasingly severe on the Mongolian Plateau, while the drivers for these changes are not clearly explored, especially whether climate change is a main factor is debated in academia. In this study, we examined the phylogenetic structure of grassland communities along five transects of climate aridity on the Mongolian Plateau, and analyzed their relations with environmental factors, with the aims to understand the formation mechanism of the grassland communities and the role of climatic factors. We surveyed grassland communities at 81 sites along the five transects, and calculated their net relatedness index(NRI) at two different quadrat scales(small scale of 1 m2 and large scale of 5 m2) to characterize the community phylogenetic structure and analyze its relationship with the key 11 environmental factors. We also calculated the generalized UniFrac distance(GUniFrac) among the grassland communities to quantify the influence of spatial distance and environmental distance on the phylogenetic β diversity. The results indicated that plant community survey using the large scale quadrat contained sufficient species to represent community compositions. The community phylogenetic structure of grasslands was significantly overdispersed at both the small and large scales, and the degree of overdispersion was greater at the large scale than at the small scale, suggesting that competitive exclusion instead of habitat filtering played a major role in determination of community composition. Altitude was the main factor affecting the community phylogenetic structure, whereas climatic factors, such as precipitation and temperatur展开更多
基金supported by the National SKA Program of China(Grant No.2020SKA0110402)the National Natural Science Foundation of China(Grant No.12073088)+1 种基金the National Key R&D Program of China(Grant No.2020YFC2201600)the Guangdong Major Project of Basic and Applied Basic Research(Grant No.2019B030302001)。
文摘Much of the research in supernova cosmology is based on an assumption that the peak luminosity of type Ia supernovae(SNe Ia),after a standardization process,is independent of the galactic environment.A series of recent studies suggested that there is a significant correlation between the standardized luminosity and the progenitor age of SNe Ia.The correlation found in the most recent work by Lee et al.[Mon.Not.R.Astron.Soc.517,2697(2022)]is strong enough to explain the extra dimming of distant SNe Ia and therefore casts doubts on the direct evidence of cosmic acceleration.The present work incorporates the uncertainties of progenitor ages,which were ignored in Lee et al.,into a fully Bayesian inference framework.We find a weaker dependence of supernova standardized luminosity on the progenitor age,but the detection of correlation remains significant(3.5σ).Assuming that such correlation can be extended to high redshift and applying it to the Pantheon SN Ia data set,we confirm that when the Hubble residual does not include intrinsic scatter,the age-bias could be the primary cause of the observed extra dimming of distant SNe Ia.Furthermore,we use the PAge formalism,which is a good approximation to many dark energy and modified gravity models,to do a model comparison.We find that if intrinsic scatter is included in the Hubble residual,the Lambda cold dark matter model remains a good fit.However,in a scenario without intrinsic scatter,the Lambda cold dark matter model faces a challenge.
基金supported by the National Key Research and Development Program of China (2016YFC0500503)the Science and Technology Program of Inner Mongolia Autonomous Region of China (20140409, 201503001)
文摘The community assembly rules and species coexistence have always been interested by ecologists. The community phylogenetic structure is the consequence of the interaction process between the organisms and the abiotic environment and has been used to explain the relative impact of abiotic and biotic factors on species co-existence. In recent years, grassland degradation and biodiversity loss have become increasingly severe on the Mongolian Plateau, while the drivers for these changes are not clearly explored, especially whether climate change is a main factor is debated in academia. In this study, we examined the phylogenetic structure of grassland communities along five transects of climate aridity on the Mongolian Plateau, and analyzed their relations with environmental factors, with the aims to understand the formation mechanism of the grassland communities and the role of climatic factors. We surveyed grassland communities at 81 sites along the five transects, and calculated their net relatedness index(NRI) at two different quadrat scales(small scale of 1 m2 and large scale of 5 m2) to characterize the community phylogenetic structure and analyze its relationship with the key 11 environmental factors. We also calculated the generalized UniFrac distance(GUniFrac) among the grassland communities to quantify the influence of spatial distance and environmental distance on the phylogenetic β diversity. The results indicated that plant community survey using the large scale quadrat contained sufficient species to represent community compositions. The community phylogenetic structure of grasslands was significantly overdispersed at both the small and large scales, and the degree of overdispersion was greater at the large scale than at the small scale, suggesting that competitive exclusion instead of habitat filtering played a major role in determination of community composition. Altitude was the main factor affecting the community phylogenetic structure, whereas climatic factors, such as precipitation and temperatur
