AI-enhanced approaches are becoming common in astronomical data analysis,including in the galaxy morphological classification.In this study we develop an approach that enhances galaxy classification by incorporating a...AI-enhanced approaches are becoming common in astronomical data analysis,including in the galaxy morphological classification.In this study we develop an approach that enhances galaxy classification by incorporating an image denoising pre-processing step,utilizing the U-Net Variational Autoencoder(VAE)architecture and effectively mitigating noise in galaxy images and leading to improved classification performance.Our methodology involves training U-Net VAEs on the Extracted Features of Galaxies Images data set.To simulate realistic observational conditions,we introduce artifacts such as projected stars,satellite trails,and diffraction patterns into clean galaxy images.The denoised images generated are evaluated using Peak Signal-to-Noise Ratio and Structural Similarity Index,to quantify the quality improvements.We utilize the denoised images for galaxy classification tasks using models such as DenseNet-201,ResNet50,VGG16 and GCNN.Simulations do reveal that the models trained on denoised images consistently outperform those trained on noisy images,thus demonstrating the efficiency of the used denoising procedure.The developed approach can be used for other astronomical data sets,via refining the VAE architecture and integrating additional pre-processing strategies,e.g.,in revealing of gravitational lenses or cosmic web structures.展开更多
Galaxy morphology detection is a pivotal task for unraveling cosmic evolutionary mechanisms,yet existing models exhibit insufficient detection accuracy for irregular and small-target galaxies.To address this,this pape...Galaxy morphology detection is a pivotal task for unraveling cosmic evolutionary mechanisms,yet existing models exhibit insufficient detection accuracy for irregular and small-target galaxies.To address this,this paper proposes the STAR-YOLO galaxy morphology detection model.The backbone network incorporates the novel Multi-scale Attentive Context Aggregation module,which deeply integrates multi-scale dilated convolution with a progressive spatial-channel attention mechanism to enhance feature extraction for irregular and small galaxies.Meanwhile,we design the lightweight Lightweight Efficient Attention Network module that reduces parameters through channel compression.The proposed Adaptive Focal Spatial-IoU loss function further improves detection performance for small galaxies through dynamic focal mechanisms and scale-invariant optimization.Evaluated on Galaxy Zoo 2 data set,our STAR-YOLO achieves 96.3%mean average precision—a 2.5%improvement over baseline models,with irregular galaxy recognition accuracy notably increasing by 9.3%.Comparative experiments demonstrate superior detection capabilities for multi-target irregular galaxies compared to stateof-the-art models,providing an innovative solution for astronomical image analysis.展开更多
We have investigated the role that different galaxy types have in galaxy-galaxy interactions in compact groups. N-body simulations of 6 galaxies consisting of a differing mixture of galaxy types were run to compare th...We have investigated the role that different galaxy types have in galaxy-galaxy interactions in compact groups. N-body simulations of 6 galaxies consisting of a differing mixture of galaxy types were run to compare the relative importance of galaxy population demographic on evolution. Three different groups with differing galaxy content were tested: all spiral, a single elliptical and 50% elliptical. Tidal interaction strength and duration were recorded to assess the importance of an interaction. A group with an equal number of spiral and elliptical galaxies has some of the longest and strongest interactions with elliptical-elliptical interactions being most significant. These elliptical-elliptical interactions are not dominated by a single large event but consist of multiple interactions. Elliptical galaxies tidally interacting with spiral galaxies, have the next strongest interaction events. For the case when a group only has a single elliptical, the largest magnitude tidal interaction is an elliptical on a spiral. Spirals interact with each other through many small interactions. For a spiral only group, the interactions are the weakest compared to the other group types. These spiral interactions are not dominated by any singular event that might be expected to lead to a merger but are more of an ongoing harassment. These results suggest that within a compact group, early type galaxies will not form via merger out of an assemblage of spiral galaxies but rather that compact groups, in effect form around an early type galaxy.展开更多
I present the results oféchelle spectroscopy of a bright H II region in the irregular galaxy IC 4662 and their comparison with results from long-slit spectroscopy of the same region.All observations were obtained...I present the results oféchelle spectroscopy of a bright H II region in the irregular galaxy IC 4662 and their comparison with results from long-slit spectroscopy of the same region.All observations were obtained with the standard spectrographs of the Southern African Large Telescope:(1)low and medium spectral resolution spectrograph Robert Stobie Spectrograph(R≈800)and(2)échelle spectrograph HRS(R=16,000–1,7000).In both types of data the intensities of most of the emission lines were measured and abundances of oxygen and N Ne,S,Ar,Cl and Fe were determined as well as physical parameters of the H II region.The chemical abundances were obtained from both types of data with the Te-method.Abundances calculated from both types of data agree to within the cited uncertainties.The analysis of theéchelle data revealed three distinct kinematic subsystems within the studied H II region:a narrow component(NC,σ≈12 km s^(-1)),a broad component(BC,σ≈40 km s^(-1)),and a very broad component(VBC,σ≈60–110 km s^(-1),detected only in the brightest emission lines).The elementa abundances for the NC and BC subsystems were determined using the Te-method.The velocity dispersion dependence on the ionization potential of elements showed no correlation for the NC,indicating a well-mixed turbulent medium,while the BC exhibited pronounced stratification,characteristic of an expanding shell.Based on a detailed analysis of the kinematics and chemical composition,it was concluded that the BC is associated with the region surrounding a Wolf-Rayet(WR)star of spectral type WN7-8.The stellar wind from this WR star interacts with a shell ejected during an earlier evolutionary stage(either as a red supergiant or a luminous blue variable LBV),which is enriched in nitrogen.These findings highlight the importance of high spectral resolution for detecting small-scale(25 pc)chemical inhomogeneities and for understanding the feedback mechanisms of massive stars in low-metallicity environments.展开更多
Utilizing a range of techniques including multi-band light curves,softness ratio analysis,structure functions,rms spectra,cross-correlation functions,and ratios of spectra from different intervals,we present a compreh...Utilizing a range of techniques including multi-band light curves,softness ratio analysis,structure functions,rms spectra,cross-correlation functions,and ratios of spectra from different intervals,we present a comprehensive study of the complex X-ray spectral variability in Seyfert 1 galaxy Ark 120,through re-analyzing its six XMMNewton observations taken between 2003 and 2014.We find a clear“softer-when-brighter”trend in the 2-10 keV power-law component over long timescales,with this trend being timescale dependent,as it is much weaker on shorter timescales,similar to that previously detected in NGC 4051.Notably,a rare“harder-when-brighter”trend is observed during one exposure,indicating dynamic changes in the spectral variability behavior of the power-law component.This exceptional exposure,with the spectral variability indeed marked by a power-law pivoting at an unusually low energy of~2 keV,suggests intricate variations in the thermal Comptonization processes within the corona.Furthermore,when the data below 2 keV are included,we identify that the soft excess component adds significant complexity to the spectral variability,such as evidenced by a transition from“harder-when-brighter”to“softer-when-brighter”during another single exposure.Such extra complexity arises because the variability of the soft excess sometimes follows and sometimes does not follow the changes in the power-law component.Our findings underscore the necessity of applying multiple analytic techniques to fully capture the multifaceted spectral variability of AGNs.展开更多
We analyze the deep Chandra data of the nearby IC 1262 group,and find that the bow-shaped structure,located about 17 kpc(25″)east of the X-ray peak,is a cold front moving eastward with a Mach number of M=0.7±0.1...We analyze the deep Chandra data of the nearby IC 1262 group,and find that the bow-shaped structure,located about 17 kpc(25″)east of the X-ray peak,is a cold front moving eastward with a Mach number of M=0.7±0.1.Furthermore,the line-of-sight velocity distribution of the member galaxies is clearly divided into two subgroups.Assuming the same mass-to-light ratio,the group is undergoing a major merger.Since the cooler core of the group as a whole is not destroyed by the merger,and the high-velocity subgroup has a component of eastward movement,it can be naturally explained that the cold front appears on the east side of the group center.展开更多
As massive amounts of image data are generated by large-scale sky survey projects, the importance of research on the morphological classification of galaxy images is growing increasingly. Deep learning, with the capab...As massive amounts of image data are generated by large-scale sky survey projects, the importance of research on the morphological classification of galaxy images is growing increasingly. Deep learning, with the capability of automatic feature extraction, exhibits remarkable performance in image classification algorithms. In the past, most of the excellent algorithm models proposed by astronomers focused on the classification of major categories and often ignored the subtle differences between galaxy categories. For this purpose, based on the DenseNet-121model, this paper attempts to introduce a variety of improvement strategies such as dynamic multi-scale convolution, learnable grouped convolution, and the squeeze-and-excitation module to optimize the performance of the model. After numerous exhaustive experimental comparisons, the DenseNet-SE4 network with excellent performance is proposed. Subsequently, we conduct comparative experiments between this network and multiple advanced convolutional models on the data set consisting of Galaxy10 DECaLS and GZD-5. We select the data of eight galaxy categories with similar morphologies, such as round smooth galaxies and barred spiral galaxies, to comprehensively test the classification ability of the model. The experimental results illustrate that the DenseNetSE4 network achieves an accuracy of 88.96%, a precision of 89.00%, a recall rate of 89.44%, and an F1-score of 89.21% on the test set, thus it has reached the highest level among the eight comparison algorithms. Moreover, the model was tested on data within different redshift intervals, demonstrating good robustness. Finally, the visualization method was employed to further validate the effectiveness and rationality of the DenseNet-SE4 network.展开更多
In the current paper,we present a study of the spatial distribution of luminous blue variables(LBVs)and various LBV candidates(c LBVs)with respect to OB associations in the galaxy M33.The identification of blue star g...In the current paper,we present a study of the spatial distribution of luminous blue variables(LBVs)and various LBV candidates(c LBVs)with respect to OB associations in the galaxy M33.The identification of blue star groups was based on the LGGS data and was carried out by two clustering algorithms with initial parameters determined during simulations of random stellar fields.We have found that the distribution of distances to the nearest OB association obtained for the LBV/c LBV sample is close to that for massive stars with Minit>20 M⊙and WolfRayet stars.This result is in good agreement with the standard assumption that LBVs represent an intermediate stage in the evolution of the most massive stars.However,some objects from the LBV/cLBV sample,particularly Fe II-emission stars,demonstrated severe isolation compared to other massive stars,which,together with certain features of their spectra,implicitly indicates that the nature of these objects and other LBVs/cLBVs may differ radically.展开更多
Based on the undisturbed, finite thickness disk gravitational potential, we carried out 3-D Monte Carlo simulations of normal pulsars. We find that their scale height evolves in a similar way for different velocity di...Based on the undisturbed, finite thickness disk gravitational potential, we carried out 3-D Monte Carlo simulations of normal pulsars. We find that their scale height evolves in a similar way for different velocity dispersions （δv）： it first increases linearly with time, reaches a peak, then gradually decreases, and finally approaches a stable asymptotic value. The initial velocity dispersion has a very large influence on the scale height. The time evolution of the scale height is studied. When the magnetic decay age is used as the time variable, the observed scale height has a similar trend as the simulated results in the linear stage, from which we derive velocity dispersions in the range 70 - 178km s^-1, which are near the statistical result of 90 - 270km s^-1 for 92 pulsars with known transverse velocities. If the characteristic age is used as the time variable, then the observed and theoretical curves roughly agree for t 〉 10^8 yr only if av 〈 25km s^-1.展开更多
The root-mean-square of non-relativistic warm dark matter particle velocities scales as v<sub>hrms</sub>(a)=v<sub>hrms</sub>(1)/a , where a is the expansion parameter of the universe. This velo...The root-mean-square of non-relativistic warm dark matter particle velocities scales as v<sub>hrms</sub>(a)=v<sub>hrms</sub>(1)/a , where a is the expansion parameter of the universe. This velocity dispersion results in a cut-off of the power spectrum of density fluctuations due to dark matter free-streaming. Let k<sub>fs </sub>(t<sub>eq</sub>) be the free-streaming comoving cut-off wavenumber at the time of equal densities of radiation and matter. We obtain , and , at 68% confidence, from the observed distributions of galaxy stellar masses and rest frame ultra-violet luminosities. This result is consistent with reionization. From the velocity dispersion cut-off mass we obtain the limits v<sub>hrms</sub>(1)k<sub>fs </sub>(t<sub>eq</sub>) >1.5 Mpc<sup>-1</sup>. These results are in agreement with previous measurements based on spiral galaxy rotation curves, and on the formation of first galaxies and reionization. These measured parameters determine the temperature-to-mass ratio of warm dark matter. This ratio happens to be in agreement with the no freeze-in and no freeze-out warm dark matter scenario of spin 0 dark matter particles decoupling early on from the standard model sector. Spin 1/2 and spin 1 dark matter are disfavored if nature has chosen the no freeze-in and no freeze-out scenario. An extension of the standard model of quarks and leptons, with scalar dark matter that couples to the Higgs boson that is in agreement with all current measurements, is briefly reviewed. Discrepancies with limits on dark matter particle mass that can be found in the literature are addressed.展开更多
We investigated the dependence of the parameters of the segments of spiral arms of the Galaxy on the age of classical Cepheids.The catalog of Cepheids(Mel’nik et al.)was divided into two samples—relatively young(P&g...We investigated the dependence of the parameters of the segments of spiral arms of the Galaxy on the age of classical Cepheids.The catalog of Cepheids(Mel’nik et al.)was divided into two samples—relatively young(P>9d)and relatively old(P<9d)objects.The parameters of the spiral structure were determined both for two samples separately and jointly for the combination of two systems of segments traced by young and old objects.For most of the segments,their parameters for young and old objects differ significantly.Taking into account the difference between the two segment systems,we obtained the estimate R0 equal to 7.23^+0.19/-0.18 kpc,which in the modern Large Magellanic Cloud(LMC)calibration corresponds to the value of R0=8.08^+0.2/-10.20|stat.^+0.38/-0.36|cal.kpc.It is shown that the displacement between the segments is not reduced to the effect of differential rotation only.To interpret this displacement for objects of Perseus and Sagittarius-2 segments,we carried out a dynamic modeling of the change in the position of the segment points when moving in the smooth gravitational field of the Galaxy.At the angular velocity of rotation of the spiral pattern Ωp=25.2±0.5 km s 1 kpc 1(Dambis et al.)the observed displacement between segments on young and old objects can be explained by the amplitude of spiral perturbations of the radial velocity of u=10±1.5 km s 1.For the constructed double system of spiral segments,it is demonstrated that the assumption of constancy of the pitch angles within each segment and the assumption that the pole of the spiral pattern is in the direction of the nominal center of the Galaxy do not contradict the data within the range of uncertainty.展开更多
This paper modifies the Farnes’ unifying theory of dark energy and dark matter which are negative-mass, created continuously from the negative-mass universe in the positive-negative mass universe pair. The first modi...This paper modifies the Farnes’ unifying theory of dark energy and dark matter which are negative-mass, created continuously from the negative-mass universe in the positive-negative mass universe pair. The first modification explains that observed dark energy is 68.6%, greater than 50% for the symmetrical positive-negative mass universe pair. This paper starts with the proposed positive-negative-mass 11D universe pair (without kinetic energy) which is transformed into the positive-negative mass 10D universe pair and the external dual gravities as in the Randall-Sundrum model, resulting in the four equal and separate universes consisting of the positive-mass 10D universe, the positive-mass massive external gravity, the negative-mass 10D universe and the negative-mass massive external gravity. The positive-mass 10D universe is transformed into 4D universe (home universe) with kinetic energy through the inflation and the Big Bang to create positive-mass dark matter which is five times of positive-mass baryonic matter. The other three universes without kinetic energy oscillate between 10D and 10D through 4D, resulting in the hidden universes when D > 4 and dark energy when D = 4, which is created continuously to our 4D home universe with the maximum dark energy = 3/4 = 75%. In the second modification to explain dark matter in the CMB, dark matter initially is not repulsive. The condensed baryonic gas at the critical surface density induces dark matter repulsive force to transform dark matter in the region into repulsive dark matter repulsing one another. The calculated percentages of dark energy, dark matter, and baryonic matter are 68.6 (as an input from the observation), 26 and 5.2, respectively, in agreement with observed 68.6, 26.5 and 4.9, respectively, and dark energy started in 4.33 billion years ago in agreement with the observed 4.71 <span style="white-space:nowrap;">±</span> 0.98 billion years ago. In conclusion, the modified Farnes’ unifying theory reinterprets the Farnes’ equations, and is a unifying theory of dark energy, dark matter, and baryonic matter in the positive-negative mass universe pair. The unifying theory explains protogalaxy and galaxy evolutions in agreement with the observations.展开更多
The nature of the principle of equivalence is explored. The path of gravitons is analyzed in an accelerating system equivalent to a gravitating system. The finite speed of the graviton results in a delay of the gravit...The nature of the principle of equivalence is explored. The path of gravitons is analyzed in an accelerating system equivalent to a gravitating system. The finite speed of the graviton results in a delay of the gravitational interaction with a particle mass. From the aberration found in the path of the graviton we derive the standard expression for the advancement of the periastron of the orbit of the mass around a star. In a similar way, by analysing the aberrations of the graviton and light paths in an accelerating reference frame, the expression for the deflection of light by a massive body is obtained identically to the standard result. We also examine the binary star system and calculate the decay in its orbital period. The decay is attributed to the redshift of the graviton frequency relative to the accelerating system. Here too, we obtain good agreement with experimental measurements. Also, hypothesizing that gravitons behave like photons, we determine the temperature of the gravitons in a binary star system and form the Bose-Einstein distribution. Finally, we show how the redshift of gravitons may be the source of dark matter, dark energy and flat line spiral galaxy rotation curves.展开更多
Based on the s-process nucleosynthesis model with the 13C（α, n）16O reaction occurring under radiative conditions in the interpulse phases, we investigate the characteristics of the distribution of neutron exposure ...Based on the s-process nucleosynthesis model with the 13C（α, n）16O reaction occurring under radiative conditions in the interpulse phases, we investigate the characteristics of the distribution of neutron exposure in low-mass Asymptotic Giant Branch （AGB） stars. We introduce a new concept, the distribution of neutron exposures of the Galaxy （NEG）, to study the chemical evolution characteristics of the Galaxy for s-process elements. Using a chemical evolution model of the Galaxy, we develop a model for the NEG and obtain the evolution results of the NEG in different epochs. The present results appear to reasonably reproduce the distribution of neutron exposures of the solar system （hereafter NES）. The main component and the strong component in the NES are built up in different epochs. The strong component of the s-process is mainly synthesised in the low-mass and metal-poor AGB stars, and the main component is produced by the s-process in the low-mass AGB stars with higher metallicities.展开更多
Understanding galaxy formation is one of the most pressing issues in cos- mology. We review the current status of galaxy formation from both an observational and a theoretical perspective, and summarize the prospects ...Understanding galaxy formation is one of the most pressing issues in cos- mology. We review the current status of galaxy formation from both an observational and a theoretical perspective, and summarize the prospects for future advances.展开更多
文摘AI-enhanced approaches are becoming common in astronomical data analysis,including in the galaxy morphological classification.In this study we develop an approach that enhances galaxy classification by incorporating an image denoising pre-processing step,utilizing the U-Net Variational Autoencoder(VAE)architecture and effectively mitigating noise in galaxy images and leading to improved classification performance.Our methodology involves training U-Net VAEs on the Extracted Features of Galaxies Images data set.To simulate realistic observational conditions,we introduce artifacts such as projected stars,satellite trails,and diffraction patterns into clean galaxy images.The denoised images generated are evaluated using Peak Signal-to-Noise Ratio and Structural Similarity Index,to quantify the quality improvements.We utilize the denoised images for galaxy classification tasks using models such as DenseNet-201,ResNet50,VGG16 and GCNN.Simulations do reveal that the models trained on denoised images consistently outperform those trained on noisy images,thus demonstrating the efficiency of the used denoising procedure.The developed approach can be used for other astronomical data sets,via refining the VAE architecture and integrating additional pre-processing strategies,e.g.,in revealing of gravitational lenses or cosmic web structures.
文摘Galaxy morphology detection is a pivotal task for unraveling cosmic evolutionary mechanisms,yet existing models exhibit insufficient detection accuracy for irregular and small-target galaxies.To address this,this paper proposes the STAR-YOLO galaxy morphology detection model.The backbone network incorporates the novel Multi-scale Attentive Context Aggregation module,which deeply integrates multi-scale dilated convolution with a progressive spatial-channel attention mechanism to enhance feature extraction for irregular and small galaxies.Meanwhile,we design the lightweight Lightweight Efficient Attention Network module that reduces parameters through channel compression.The proposed Adaptive Focal Spatial-IoU loss function further improves detection performance for small galaxies through dynamic focal mechanisms and scale-invariant optimization.Evaluated on Galaxy Zoo 2 data set,our STAR-YOLO achieves 96.3%mean average precision—a 2.5%improvement over baseline models,with irregular galaxy recognition accuracy notably increasing by 9.3%.Comparative experiments demonstrate superior detection capabilities for multi-target irregular galaxies compared to stateof-the-art models,providing an innovative solution for astronomical image analysis.
文摘We have investigated the role that different galaxy types have in galaxy-galaxy interactions in compact groups. N-body simulations of 6 galaxies consisting of a differing mixture of galaxy types were run to compare the relative importance of galaxy population demographic on evolution. Three different groups with differing galaxy content were tested: all spiral, a single elliptical and 50% elliptical. Tidal interaction strength and duration were recorded to assess the importance of an interaction. A group with an equal number of spiral and elliptical galaxies has some of the longest and strongest interactions with elliptical-elliptical interactions being most significant. These elliptical-elliptical interactions are not dominated by a single large event but consist of multiple interactions. Elliptical galaxies tidally interacting with spiral galaxies, have the next strongest interaction events. For the case when a group only has a single elliptical, the largest magnitude tidal interaction is an elliptical on a spiral. Spirals interact with each other through many small interactions. For a spiral only group, the interactions are the weakest compared to the other group types. These spiral interactions are not dominated by any singular event that might be expected to lead to a merger but are more of an ongoing harassment. These results suggest that within a compact group, early type galaxies will not form via merger out of an assemblage of spiral galaxies but rather that compact groups, in effect form around an early type galaxy.
基金support from the National Research Foundation(NRF)of South Africa。
文摘I present the results oféchelle spectroscopy of a bright H II region in the irregular galaxy IC 4662 and their comparison with results from long-slit spectroscopy of the same region.All observations were obtained with the standard spectrographs of the Southern African Large Telescope:(1)low and medium spectral resolution spectrograph Robert Stobie Spectrograph(R≈800)and(2)échelle spectrograph HRS(R=16,000–1,7000).In both types of data the intensities of most of the emission lines were measured and abundances of oxygen and N Ne,S,Ar,Cl and Fe were determined as well as physical parameters of the H II region.The chemical abundances were obtained from both types of data with the Te-method.Abundances calculated from both types of data agree to within the cited uncertainties.The analysis of theéchelle data revealed three distinct kinematic subsystems within the studied H II region:a narrow component(NC,σ≈12 km s^(-1)),a broad component(BC,σ≈40 km s^(-1)),and a very broad component(VBC,σ≈60–110 km s^(-1),detected only in the brightest emission lines).The elementa abundances for the NC and BC subsystems were determined using the Te-method.The velocity dispersion dependence on the ionization potential of elements showed no correlation for the NC,indicating a well-mixed turbulent medium,while the BC exhibited pronounced stratification,characteristic of an expanding shell.Based on a detailed analysis of the kinematics and chemical composition,it was concluded that the BC is associated with the region surrounding a Wolf-Rayet(WR)star of spectral type WN7-8.The stellar wind from this WR star interacts with a shell ejected during an earlier evolutionary stage(either as a red supergiant or a luminous blue variable LBV),which is enriched in nitrogen.These findings highlight the importance of high spectral resolution for detecting small-scale(25 pc)chemical inhomogeneities and for understanding the feedback mechanisms of massive stars in low-metallicity environments.
基金supported by the National Natural Science Foundation of China (NSFC,grant Nos.12033006,12192221,and 123B2042)the Cyrus Chun Ying Tang Foundationsfunded by ESA Member States and NASA
文摘Utilizing a range of techniques including multi-band light curves,softness ratio analysis,structure functions,rms spectra,cross-correlation functions,and ratios of spectra from different intervals,we present a comprehensive study of the complex X-ray spectral variability in Seyfert 1 galaxy Ark 120,through re-analyzing its six XMMNewton observations taken between 2003 and 2014.We find a clear“softer-when-brighter”trend in the 2-10 keV power-law component over long timescales,with this trend being timescale dependent,as it is much weaker on shorter timescales,similar to that previously detected in NGC 4051.Notably,a rare“harder-when-brighter”trend is observed during one exposure,indicating dynamic changes in the spectral variability behavior of the power-law component.This exceptional exposure,with the spectral variability indeed marked by a power-law pivoting at an unusually low energy of~2 keV,suggests intricate variations in the thermal Comptonization processes within the corona.Furthermore,when the data below 2 keV are included,we identify that the soft excess component adds significant complexity to the spectral variability,such as evidenced by a transition from“harder-when-brighter”to“softer-when-brighter”during another single exposure.Such extra complexity arises because the variability of the soft excess sometimes follows and sometimes does not follow the changes in the power-law component.Our findings underscore the necessity of applying multiple analytic techniques to fully capture the multifaceted spectral variability of AGNs.
基金supported by the National Natural Science Foundation of China(grant Nos.11103057 and 12003014).
文摘We analyze the deep Chandra data of the nearby IC 1262 group,and find that the bow-shaped structure,located about 17 kpc(25″)east of the X-ray peak,is a cold front moving eastward with a Mach number of M=0.7±0.1.Furthermore,the line-of-sight velocity distribution of the member galaxies is clearly divided into two subgroups.Assuming the same mass-to-light ratio,the group is undergoing a major merger.Since the cooler core of the group as a whole is not destroyed by the merger,and the high-velocity subgroup has a component of eastward movement,it can be naturally explained that the cold front appears on the east side of the group center.
基金supported by the National Natural Science Foundation of China(NSFC,grant No.U1731128).
文摘As massive amounts of image data are generated by large-scale sky survey projects, the importance of research on the morphological classification of galaxy images is growing increasingly. Deep learning, with the capability of automatic feature extraction, exhibits remarkable performance in image classification algorithms. In the past, most of the excellent algorithm models proposed by astronomers focused on the classification of major categories and often ignored the subtle differences between galaxy categories. For this purpose, based on the DenseNet-121model, this paper attempts to introduce a variety of improvement strategies such as dynamic multi-scale convolution, learnable grouped convolution, and the squeeze-and-excitation module to optimize the performance of the model. After numerous exhaustive experimental comparisons, the DenseNet-SE4 network with excellent performance is proposed. Subsequently, we conduct comparative experiments between this network and multiple advanced convolutional models on the data set consisting of Galaxy10 DECaLS and GZD-5. We select the data of eight galaxy categories with similar morphologies, such as round smooth galaxies and barred spiral galaxies, to comprehensively test the classification ability of the model. The experimental results illustrate that the DenseNetSE4 network achieves an accuracy of 88.96%, a precision of 89.00%, a recall rate of 89.44%, and an F1-score of 89.21% on the test set, thus it has reached the highest level among the eight comparison algorithms. Moreover, the model was tested on data within different redshift intervals, demonstrating good robustness. Finally, the visualization method was employed to further validate the effectiveness and rationality of the DenseNet-SE4 network.
文摘In the current paper,we present a study of the spatial distribution of luminous blue variables(LBVs)and various LBV candidates(c LBVs)with respect to OB associations in the galaxy M33.The identification of blue star groups was based on the LGGS data and was carried out by two clustering algorithms with initial parameters determined during simulations of random stellar fields.We have found that the distribution of distances to the nearest OB association obtained for the LBV/c LBV sample is close to that for massive stars with Minit>20 M⊙and WolfRayet stars.This result is in good agreement with the standard assumption that LBVs represent an intermediate stage in the evolution of the most massive stars.However,some objects from the LBV/cLBV sample,particularly Fe II-emission stars,demonstrated severe isolation compared to other massive stars,which,together with certain features of their spectra,implicitly indicates that the nature of these objects and other LBVs/cLBVs may differ radically.
基金Supported by the National Natural Science Foundation of China.
文摘Based on the undisturbed, finite thickness disk gravitational potential, we carried out 3-D Monte Carlo simulations of normal pulsars. We find that their scale height evolves in a similar way for different velocity dispersions （δv）： it first increases linearly with time, reaches a peak, then gradually decreases, and finally approaches a stable asymptotic value. The initial velocity dispersion has a very large influence on the scale height. The time evolution of the scale height is studied. When the magnetic decay age is used as the time variable, the observed scale height has a similar trend as the simulated results in the linear stage, from which we derive velocity dispersions in the range 70 - 178km s^-1, which are near the statistical result of 90 - 270km s^-1 for 92 pulsars with known transverse velocities. If the characteristic age is used as the time variable, then the observed and theoretical curves roughly agree for t 〉 10^8 yr only if av 〈 25km s^-1.
文摘The root-mean-square of non-relativistic warm dark matter particle velocities scales as v<sub>hrms</sub>(a)=v<sub>hrms</sub>(1)/a , where a is the expansion parameter of the universe. This velocity dispersion results in a cut-off of the power spectrum of density fluctuations due to dark matter free-streaming. Let k<sub>fs </sub>(t<sub>eq</sub>) be the free-streaming comoving cut-off wavenumber at the time of equal densities of radiation and matter. We obtain , and , at 68% confidence, from the observed distributions of galaxy stellar masses and rest frame ultra-violet luminosities. This result is consistent with reionization. From the velocity dispersion cut-off mass we obtain the limits v<sub>hrms</sub>(1)k<sub>fs </sub>(t<sub>eq</sub>) >1.5 Mpc<sup>-1</sup>. These results are in agreement with previous measurements based on spiral galaxy rotation curves, and on the formation of first galaxies and reionization. These measured parameters determine the temperature-to-mass ratio of warm dark matter. This ratio happens to be in agreement with the no freeze-in and no freeze-out warm dark matter scenario of spin 0 dark matter particles decoupling early on from the standard model sector. Spin 1/2 and spin 1 dark matter are disfavored if nature has chosen the no freeze-in and no freeze-out scenario. An extension of the standard model of quarks and leptons, with scalar dark matter that couples to the Higgs boson that is in agreement with all current measurements, is briefly reviewed. Discrepancies with limits on dark matter particle mass that can be found in the literature are addressed.
基金support from the Russian Science Foundation,Grant No.18-12-00050。
文摘We investigated the dependence of the parameters of the segments of spiral arms of the Galaxy on the age of classical Cepheids.The catalog of Cepheids(Mel’nik et al.)was divided into two samples—relatively young(P>9d)and relatively old(P<9d)objects.The parameters of the spiral structure were determined both for two samples separately and jointly for the combination of two systems of segments traced by young and old objects.For most of the segments,their parameters for young and old objects differ significantly.Taking into account the difference between the two segment systems,we obtained the estimate R0 equal to 7.23^+0.19/-0.18 kpc,which in the modern Large Magellanic Cloud(LMC)calibration corresponds to the value of R0=8.08^+0.2/-10.20|stat.^+0.38/-0.36|cal.kpc.It is shown that the displacement between the segments is not reduced to the effect of differential rotation only.To interpret this displacement for objects of Perseus and Sagittarius-2 segments,we carried out a dynamic modeling of the change in the position of the segment points when moving in the smooth gravitational field of the Galaxy.At the angular velocity of rotation of the spiral pattern Ωp=25.2±0.5 km s 1 kpc 1(Dambis et al.)the observed displacement between segments on young and old objects can be explained by the amplitude of spiral perturbations of the radial velocity of u=10±1.5 km s 1.For the constructed double system of spiral segments,it is demonstrated that the assumption of constancy of the pitch angles within each segment and the assumption that the pole of the spiral pattern is in the direction of the nominal center of the Galaxy do not contradict the data within the range of uncertainty.
文摘This paper modifies the Farnes’ unifying theory of dark energy and dark matter which are negative-mass, created continuously from the negative-mass universe in the positive-negative mass universe pair. The first modification explains that observed dark energy is 68.6%, greater than 50% for the symmetrical positive-negative mass universe pair. This paper starts with the proposed positive-negative-mass 11D universe pair (without kinetic energy) which is transformed into the positive-negative mass 10D universe pair and the external dual gravities as in the Randall-Sundrum model, resulting in the four equal and separate universes consisting of the positive-mass 10D universe, the positive-mass massive external gravity, the negative-mass 10D universe and the negative-mass massive external gravity. The positive-mass 10D universe is transformed into 4D universe (home universe) with kinetic energy through the inflation and the Big Bang to create positive-mass dark matter which is five times of positive-mass baryonic matter. The other three universes without kinetic energy oscillate between 10D and 10D through 4D, resulting in the hidden universes when D > 4 and dark energy when D = 4, which is created continuously to our 4D home universe with the maximum dark energy = 3/4 = 75%. In the second modification to explain dark matter in the CMB, dark matter initially is not repulsive. The condensed baryonic gas at the critical surface density induces dark matter repulsive force to transform dark matter in the region into repulsive dark matter repulsing one another. The calculated percentages of dark energy, dark matter, and baryonic matter are 68.6 (as an input from the observation), 26 and 5.2, respectively, in agreement with observed 68.6, 26.5 and 4.9, respectively, and dark energy started in 4.33 billion years ago in agreement with the observed 4.71 <span style="white-space:nowrap;">±</span> 0.98 billion years ago. In conclusion, the modified Farnes’ unifying theory reinterprets the Farnes’ equations, and is a unifying theory of dark energy, dark matter, and baryonic matter in the positive-negative mass universe pair. The unifying theory explains protogalaxy and galaxy evolutions in agreement with the observations.
文摘The nature of the principle of equivalence is explored. The path of gravitons is analyzed in an accelerating system equivalent to a gravitating system. The finite speed of the graviton results in a delay of the gravitational interaction with a particle mass. From the aberration found in the path of the graviton we derive the standard expression for the advancement of the periastron of the orbit of the mass around a star. In a similar way, by analysing the aberrations of the graviton and light paths in an accelerating reference frame, the expression for the deflection of light by a massive body is obtained identically to the standard result. We also examine the binary star system and calculate the decay in its orbital period. The decay is attributed to the redshift of the graviton frequency relative to the accelerating system. Here too, we obtain good agreement with experimental measurements. Also, hypothesizing that gravitons behave like photons, we determine the temperature of the gravitons in a binary star system and form the Bose-Einstein distribution. Finally, we show how the redshift of gravitons may be the source of dark matter, dark energy and flat line spiral galaxy rotation curves.
基金Supported by the National Natural Science Foundation of China.
文摘Based on the s-process nucleosynthesis model with the 13C（α, n）16O reaction occurring under radiative conditions in the interpulse phases, we investigate the characteristics of the distribution of neutron exposure in low-mass Asymptotic Giant Branch （AGB） stars. We introduce a new concept, the distribution of neutron exposures of the Galaxy （NEG）, to study the chemical evolution characteristics of the Galaxy for s-process elements. Using a chemical evolution model of the Galaxy, we develop a model for the NEG and obtain the evolution results of the NEG in different epochs. The present results appear to reasonably reproduce the distribution of neutron exposures of the solar system （hereafter NES）. The main component and the strong component in the NES are built up in different epochs. The strong component of the s-process is mainly synthesised in the low-mass and metal-poor AGB stars, and the main component is produced by the s-process in the low-mass AGB stars with higher metallicities.
文摘Understanding galaxy formation is one of the most pressing issues in cos- mology. We review the current status of galaxy formation from both an observational and a theoretical perspective, and summarize the prospects for future advances.
