In this paper we explore the formation of bars and present the bulge and bar properties and their correlations for a sample of lenticular barred(SB0)and lenticular unbarred(S0)galaxies in the central region of the Com...In this paper we explore the formation of bars and present the bulge and bar properties and their correlations for a sample of lenticular barred(SB0)and lenticular unbarred(S0)galaxies in the central region of the Coma Cluster using HST/ACS data.In our sample,we identified bar features using the luminosity profile decomposition software GALFIT.We classified the bulges based on Sérsic index and Kormendy relation.We found that the average mass of the bulge in SB0 galaxies is 1.48×10^(10)M☉whereas the average mass of the bulge in S0 galaxies is 4.3×10^(10)M☉.We observe that SB0 galaxies show lower bulge concentration,low mass and also smaller B/T values compared to S0 galaxies.Using the Kormendy relation,we found that among the lenticular barred galaxies,82%have classical bulges and 18%have pseudo bulges.These classical bulges have low masses compared to the classical bulges of unbarred galaxies.S0,galaxies with massive classical bulges do not host bars.We also found that for all SB0s the bulge effective radius is less than the bar effective radius.SB0 galaxies with classical bulges suggest that the bar may have formed by mergers.展开更多
We study the relationship between isophotal shapes, central light profiles and kinematic properties of early-type galaxies (ETGs) based on a compiled sample of 184 ETGs. These sample galaxies are included in Data Re...We study the relationship between isophotal shapes, central light profiles and kinematic properties of early-type galaxies (ETGs) based on a compiled sample of 184 ETGs. These sample galaxies are included in Data Release 8 of the Sloan Digital Sky Survey and have central light profiles and kinematic properties available from the literature, which were compiled from observations by the Hubble Space Telescope and the ATLAS3D integral-field spectrograph, respectively. We find that there is only a weak correlation between the isophotal shape (a4/a) and the central light profile (within 1 kpc) of ETGs. About two-fifths of "core" galaxies have disky isophotes, and one-third of "power-law" galaxies are boxy. Our statistical results also show that there are weak correlations between galaxy luminosity and dynamical mass with a4/a, but such correlations are tighter with a central light profile. Moreover, no clear link has been found between the isophotal shape and the Sersic index. Comparisons show that there are similar correlations between a4/a and ellipticity, and between a4/a and specific angular momentum ARo/2 for "power-law" ETGs, but there are no such correlations for "core" ETGs. Therefore, we speculate that the bimodal classifications of ETGs are not as simple as previously thought, though we also find that the disky ETGs with highest a4/a are more elongated and fast rotators.展开更多
An optical photometric observation with the Beijing-Arizona-Taiwan- Connecticut (BATC) multicolor system is carried out for A98 (z =0.104), a galaxy cluster with two large enhancements in X-ray surface brightness....An optical photometric observation with the Beijing-Arizona-Taiwan- Connecticut (BATC) multicolor system is carried out for A98 (z =0.104), a galaxy cluster with two large enhancements in X-ray surface brightness. Spectral energy distributions (SEDs) covering 15 intermediate bands are obtained for all sources detected down to V - 20 mag in a field of 58′× 58′. After star-galaxy separation with colorcolor diagrams, a photometric redshift technique is applied to the galaxy sample for further membership determination. The color-magnitude relation is taken as a further restriction of the early-type cluster galaxies. As a result, a list of 198 faint member galaxies is achieved. Based on the newly generated sample of member galaxies, the dynamical substructures, A98N, A98S, and A98W, are investigated in detail. A separate galaxy group, A98X, is also found to the south of the main concentration of A98, which is gravitationally unbound to A98. For 74 spectroscopically confirmed member galaxies, the environmental effect on the star formation history is investigated. The bright galaxies in the core region are found to have shorter time scales of star formation, longer mean stellar ages, and higher interstellar medium metallicities, which can be interpreted in the context of the hierarchical cosmological scenario.展开更多
From photometric observations and star counts, the existence of a bar in the central few kpc of the Galaxy is suggested. It is generally thought that our Galaxy is surrounded by a massive invisible halo. The gravitati...From photometric observations and star counts, the existence of a bar in the central few kpc of the Galaxy is suggested. It is generally thought that our Galaxy is surrounded by a massive invisible halo. The gravitational potential of the Galaxy is therefore made nonaxisymmetric generated by the central triaxial bar, by the outer triaxial halo, and/or by the spiral structures. Selecting nearly 300 open clusters with complete spatial velocity measurements and ages, we were able to construct the rotation curve of the Milky Way within a range of 3 kpc of the Sun. Using a dynamic model for an assumed elliptical disk, a clear weak elliptical potential of the disk with ellipticity of ε(R0) = 0.060 4± 0.012 is detected, the Sun is found to be near the minor axis, displaced by 30°±3°. The motion of the clusters is suggested to be on an oval orbit rather than on a circular one.展开更多
By using the Mixture Model and radial velocity data from CfA redshift catalogue, we resolve the substructures of the Virgo cluster. Distances of three main subclusters are determined by the Tully-Fisher galaxies, they...By using the Mixture Model and radial velocity data from CfA redshift catalogue, we resolve the substructures of the Virgo cluster. Distances of three main subclusters are determined by the Tully-Fisher galaxies, they are 18.0±1.3Mpc, 25.0±2 3Mpc and 30.9±3.1Mpc respectively, which implicate that they are independent clusters, and the Virgo area has a significant depth in the line-of -sight direction.展开更多
An investigation on the possible dynamical models of the core galaxy NGC 1399 is performed.Because early-type galaxies are likely to be formed through merging events, remnant rings are considered in the modeling proce...An investigation on the possible dynamical models of the core galaxy NGC 1399 is performed.Because early-type galaxies are likely to be formed through merging events, remnant rings are considered in the modeling process.A numerical survey over three parameters is employed to obtain the best-fit models that are completely consistent with observations.It is found that the inner slope of the dark matter profile is cuspy for this core galaxy.The existence of remnant rings in best-fit models indicates a merging history.The remnant ring explains the flattened surface brightness and thus could be the physical counterpart of the core structure of NGC 1399.展开更多
We study the dynamical states of the 30 most massive galaxy clusters in the TNG100 simulation at redshift z = 0 using three types of tracers: stars, dark matter particles and satellite galaxies. If the massive galaxy ...We study the dynamical states of the 30 most massive galaxy clusters in the TNG100 simulation at redshift z = 0 using three types of tracers: stars, dark matter particles and satellite galaxies. If the massive galaxy cluster is spherically symmetric and relaxed, we can obtain the underlying total mass distribution accurately from its dynamical tracers using the spherical Jeans equations. Although the three tracers of clusters have very different number densities, velocity dispersions and anisotropies, they still trace the same total mass profile. We obtain the total mass profiles of clusters using these tracers separately and compare them with the true mass distributions. We find that:(1) the kinematics of dark matter trace the total mass of all clusters well and the mass inferred from dark matter are generally consistent with the true mass profiles with relative deviations smaller than ~ 25% at all radii;(2) stars in ~ 60% massive clusters are approaching equilibrium and the total mass of these clusters inferred from stars have relative deviations smaller than ~50% at all radii. Stellar substructures are rich and the mass inferred from stars tend to be over-estimated in the inner region;and(3) satellite galaxies are unrelaxed in the inner region and become more relaxed as the radius increases. The total mass inferred from satellites are under-estimated in all regions.展开更多
Convincing evidence for a past interaction between the two rich clusters A399 and A401 was recently found in the X-ray imaging observations. We examine the structure and dynamics of this pair of galaxy clusters. A mix...Convincing evidence for a past interaction between the two rich clusters A399 and A401 was recently found in the X-ray imaging observations. We examine the structure and dynamics of this pair of galaxy clusters. A mixture-modeling algorithm was applied to obtain a robust partition into two clusters, which allowed us to discuss the virial mass and velocity distribution of each cluster. Assuming that these two clusters follow a linear orbit and they have once experienced a close encounter, we model the binary cluster as a two-body system. As a result, four gravitationally bound solutions are obtained. The recent X-ray observations seem to favor a scenario in which the two clusters with a true separation of 5.4h-1 Mpc are currently expanding at 583 km s-1 along a direction with a projection angle of 67.5°, and they will reach a maximum extent of 5.65 h-1 Mpc in about 1.0 h-1 Gyr.展开更多
We review the long-term survival chances of young massive star clusters (YMCs), hallmarks of intense starburst episodes often associated with Violent galaxy interactions. We address the key question as to whether at...We review the long-term survival chances of young massive star clusters (YMCs), hallmarks of intense starburst episodes often associated with Violent galaxy interactions. We address the key question as to whether at least some of these YMCs can be considered protoglobular clusters (GCs), in which case these would be expected to evolve into counterparts of the ubiquitous old GCs believed to be among the oldest galactic building blocks. In the absence of significant external perturbations, the key factor determining a cluster's long-term survival chances is the shape of its stellar initial mass function (IMF). It is, however, not straightforward to assess the IMF shape in unresolved extragalactic YMCs. We discuss in detail the promise of using high-resolution spectroscopy to make progress towards this goal, as well as the numerous pitfalls associated with this approach. We also discuss the latest progress in worldwide efforts to better understand the evolution of entire cluster systems, the disruption processes they are affected by, and whether we can use recently gained insights to determine the nature of at least some of the YMCs observed in extragalactic starbursts as proto-GCs. We conclude that there is an increasing body of evidence that GC formation appears to be continuing until today; their long-term evolution crucially depends on their environmental conditions, however.展开更多
A cosmological model was developed using the equation of state of photon gas, as well as cosmic time. The primary objective of this model is to see if determining the observed rotation speed of galactic matter is poss...A cosmological model was developed using the equation of state of photon gas, as well as cosmic time. The primary objective of this model is to see if determining the observed rotation speed of galactic matter is possible, without using dark matter (halo) as a parameter. To do so, a numerical application of the evolution of variables in accordance with cosmic time and a new state equation was developed to determine precise, realistic values for a number of cosmological parameters, such as energy of the universe <i>U</i>, cosmological constant <i>E</i><sub>Λ</sub>, curvature of space <i>k</i>, energy density <i>ρ</i><sub>Λ<i>e</i></sub>, age of the universe <i>t</i><sub>Ω</sub> (part 1). That energy of the universe, when taken into consideration during the formation of the first galaxies (<1 [Gy]), provides a relatively adequate explanation of the non-Keplerian rotation of galactic masses (part 2). Indeed, such residual, non-baryonic energy, when considered in Newton’s gravity equation, adds the term <i>F</i><sub>Λ</sub>(<i>r</i>), which can partially explain, without recourse to dark matter, the rotations of some galaxies, such as M33, UGC12591, UGC2885, NGC3198, NGC253, DDO161, UDG44, the MW and the Coma cluster. Today, in the MW, that cosmological gravity force is in the order of 10<sup>26</sup> times smaller than the conventional gravity force. The model predicts an acceleration of the mass in the universe (<i>q</i>~-0.986);the energy associated with curvature <i>E<sub>k</sub></i> is the driving force behind the expansion of the universe, rather than the energy associated with the cosmological constant <i>E</i><sub>Λ</sub>. An equation to determine expansion is obtained using the energy form of the Friedmann equation relative to Planck power <i>P<sub>P</sub></i> and cosmic time or Planck force <i>F<sub>P</sub></i> acting at the frontier of the universe moving at <i>c</i>. This constant Planck force, from unknown sources, acts everywhere to the expansion of the universe as a stretching effect on the volume. Finally, the model partly explains the value a<sub>0</sub> of the MOND theory. Indeed, <i>a</i><sub>0</sub> is not a true constant, but depends on the cosmological constant at the time the great structures were formed (~1 [Gy]), as well as an adjustment of the typical mass and dimension of those great structures, such as galaxies. The constant a<sub>0</sub> is a different expression of the cosmological gravity force <i>F</i><sub>Λ</sub> as expressed by the cosmological constant, Λ, acting through the energy-mass equivalent during the formation of the structures. It does not put in question the value of <i>G</i>.展开更多
Open clusters(OCs)are infrequent survivors of embedded clusters gestated in molecular clouds.Up to now,little is known about the initial conditions for the formation of OCs.Here,we studied this issue using high-precis...Open clusters(OCs)are infrequent survivors of embedded clusters gestated in molecular clouds.Up to now,little is known about the initial conditions for the formation of OCs.Here,we studied this issue using high-precision astrometric parameters provided by Gaia data release 3.The statistics show that the peculiar motion velocities of OCs vary slightly from infancy to old age,providing a remarkable opportunity to use OCs to trace their progenitors.Adopting a dynamical method,we derived the masses of the progenitor clumps where OCs were born,which have statistical characteristics comparable to previously known results for clumps observed in the Galaxy.Moreover,the masses of the progenitor clumps of OCs indicate they should be capable of gestating massive O-type stars.In fact,after inspecting the observed OCs and O-type stars,we found that there are many O-type stars in OCs.The destructive stellar feedback from O-type stars may disintegrate the vast majority of embedded clusters,and only those sufficiently dense ones can survive as OCs.展开更多
The kinematical parameters,spatial shape and structure of the open cluster IC 2391 and the associated stellar stream are studied here using Gaia Data Release 2(GDR2) astrometry data.The apex positions are determined f...The kinematical parameters,spatial shape and structure of the open cluster IC 2391 and the associated stellar stream are studied here using Gaia Data Release 2(GDR2) astrometry data.The apex positions are determined for the open cluster IC 2391(data taken from Cantat-Gaudin et al.) and for the kinematical stream’s stars mentioned in Montes et al.employing both convergent point and AD-diagram methods.The values of apex coordinates are:(A,D)CP=(6.~h17 ± 0.~h004,-6.°88 ± 0.°381;for cluster) and(6.~h07 ± 0.~h007,-5.°00 ± 0.°447;stream),and(A0,D0) =(6.~h12 ± 0.~h004,-3.°4 ± 0.°3;cluster) and(6.~h21 ±0.~h007,-11.°895 ± 0.°290;stream).The results are in good agreement with the previously calculated values.The positions of the stars in the disk and the spatial dispersion velocities are determined.The paths of cluster and associated stream are traced in the disk by orbit calculation back in time to their places of formation.A possible genetic relationship between the cluster and stream has been detected.The approximation of the spatial and kinematical shape of the stream and the cluster is made.According to this study,even though currently the cluster and stream seem to have a spatial difference in their locations,they appear to have formed in the same region of the Galactic disk.展开更多
The age pattern across spiral arms is one of the key observational features utilised to study the dynamic nature of the Galaxy’s spiral structure.With the most updated samples of high-mass star formation region(HMSFR...The age pattern across spiral arms is one of the key observational features utilised to study the dynamic nature of the Galaxy’s spiral structure.With the most updated samples of high-mass star formation region(HMSFR)masers,O stars and open clusters,we investigated their distributions and kinematic properties in the vicinity of the Sun.We found that the Sagittarius-Carina Arm traced by HMSFRs,O stars((?)10 Myr)and young open clusters(<30 Myr)seem to deviate gradually towards the Galactic Anticenter(GAC)direction.The Local Arm traced by HMSFRs,O stars,young clusters and also mediumyoung clusters(30-100 Myr)are inclined to gradually deviate toward the Galactic Center(GC)direction.The properties for the Local Arm are supported by a simplified simulation of cluster motions in the Galaxy.Indications of systematic motions in the circular and radial velocities are noticed for the old open clusters(>200 Myr).These results are consistent with the idea that star formation can be triggered by spiral shocks of density waves,and indicate that the corotation radius of the Galaxy is located between the SagittariusCarina Arm and the Local Arm,close to the Solar circle.展开更多
Fitting parametric models to globular clusters’structural profiles has been essential for the study of stellar dynamics.It provides their important structural parameters,such as the concentrations and core radii of t...Fitting parametric models to globular clusters’structural profiles has been essential for the study of stellar dynamics.It provides their important structural parameters,such as the concentrations and core radii of the clusters.However,existing parametric models can apply only to non-collapsing-core clusters in the early relaxation-evolution stage.Hence,a single parametric model cannot provide globular clusters’structural parameters in both the early and late evolution stages.We have recently found an accurate spectral solution for the self-similar orbit-averaged Fokker-Planck(OAFP)equation to model collapsingcore clusters at the late evolution stage.The present work establishes a new parametric model by combining the self-similar OAFP-and polytropic-models.Although it is a single-mass and isotropic model,the new model applies to at least fifty-five Galactic globular clusters with resolved cores in all the evolution stages.As a main result,we show the characteristics of the relaxation times against the concentrations of the clusters.We also affirm that the structures of low-concentration clusters are polytropic in the Milky Way.展开更多
We present a new determination of the Galactocentric distance by a pure kinematical model. Two subgroups of components from the Galactic thin disk, the O-B5 stars and the Galactic open clusters, were selected for our ...We present a new determination of the Galactocentric distance by a pure kinematical model. Two subgroups of components from the Galactic thin disk, the O-B5 stars and the Galactic open clusters, were selected for our analysis. On the basis of kinematical data of around 1200 O-B5 stars, we obtained an estimated value of Ro=8.25-4-0.79 kpc, while a similar evaluation from 270 Galactic open clusters gives Ro=7.95-4-0.62 kpc. Considering the scatter of Ro given by individual investigators with different methods, our present determinations agree well with the best value proposed by Reid.展开更多
Absolute proper motions and radial velocities of 202 open clusters in the solar neighborhood, which can be used as tracers of the Galactic disk, are used to investigate the kinematics of the Galaxy in the solar vicini...Absolute proper motions and radial velocities of 202 open clusters in the solar neighborhood, which can be used as tracers of the Galactic disk, are used to investigate the kinematics of the Galaxy in the solar vicinity, including the mean heliocentric velocity components (u1, u2, u3) of the open cluster system, the characteristic velocity dispersions (σ1,σ2,σ3), Oort constants (A, B) and the large-scale radial motion parameters (C, D) of the Galaxy. The results derived from the observational data of proper motions and radial velocities of a subgroup of 117 thin disk young open clusters by means of a maximum likelihood algorithm are: (u1,u2,u3) = (-16.1 ± 1.0,-7.9 ±1.4,-10.4±1.5) km·s^-1, (σ1,σ2,σ3) = (17.0±0.7, 12.2±0.9, 8.0±1.3) km·S^-1, (A, B) = (14.8±1.0, - 13.0±2.7) km·s^-1 kpc^-1, and (C, D) = (1.5 ± 0.7, -1.2 ±1.5) km·s^-1 kpc^-1. A discussion on the results and comparisons with what was obtained by other authors is given.展开更多
Abstract We report the discovery of 45 high-velocity extreme horizontal branch (EHB) stars in the globular cluster Omega Centauri (NGC 5139). The tangential ve- locities of these EHB stars are determined to be in ...Abstract We report the discovery of 45 high-velocity extreme horizontal branch (EHB) stars in the globular cluster Omega Centauri (NGC 5139). The tangential ve- locities of these EHB stars are determined to be in the range 93-313 km s^-1, with an average uncertainty of -27 km s^-1. The central escape velocity of the cluster is determined to be in the range 60~105 km s^-1. These EHB stars are significantly more concentrated toward the cluster core compared with other cluster members. The formation mechanisms of these EHB stars are discussed. Our conclusions can be sum- marized as follows: (1) A comparison of the tangential velocities of these EHB stars to the central escape velocity of the cluster shows that most if not all of these EHB stars are unbound to the cluster; (2) These EHB stars obtained high velocities in the central cluster region no longer than - 1 Myr ago and may be subsequently ejected from the cluster in the next -1 Myr; (3) If the progenitors of these EHB stars were single stars, then they may have experienced a fast mass-loss process. If the progen- itors were in close binaries, then they may have formed through disruptions by the intermediate-mass black hole in the cluster center.展开更多
This paper presents multicolor optical photometry of the nearby galaxy cluster Abell 119 (z = 0.0442) with the Beijing-Arizona-Taiwan-Connecticut system of 15 intermediate bands. Within the BATC field of view of 58...This paper presents multicolor optical photometry of the nearby galaxy cluster Abell 119 (z = 0.0442) with the Beijing-Arizona-Taiwan-Connecticut system of 15 intermediate bands. Within the BATC field of view of 58'× 58', there are 368 galaxies with known spectroscopic redshifts, including 238 member galaxies (called sample I). Based on the spectral energy distributions of 1376 galaxies brighter than iBATC ---- 19.5, the photometric redshift technique and the color-magnitude relation of early-type galaxies are applied to select faint member galaxies. As a result, 117 faint galaxies were selected as new member galaxies. Combined with sample I, an enlarged sample (called sample II) of 355 member galaxies is obtained. Spatial distribution and localized velocity structure for two samples demonstrate that A119 is a dynami- cally complex cluster with at least three prominent substructures in the central region within 1 Mpc. A large velocity dispersion for the central clump indicates a merging along the line of sight. No significant evidence for morphology or luminosity segrega- tions is found in either sample. With the PEGASE evolutionary synthesis model, the environmental effect on the properties of star formation is confirmed. Faint galaxies in the low-density region tend to have longer time scales of star formation, smaller mean stellar ages, and lower metallicities in their interstellar medium, which is in agreement with the context of the hierarchical cosmological scenario.展开更多
文摘In this paper we explore the formation of bars and present the bulge and bar properties and their correlations for a sample of lenticular barred(SB0)and lenticular unbarred(S0)galaxies in the central region of the Coma Cluster using HST/ACS data.In our sample,we identified bar features using the luminosity profile decomposition software GALFIT.We classified the bulges based on Sérsic index and Kormendy relation.We found that the average mass of the bulge in SB0 galaxies is 1.48×10^(10)M☉whereas the average mass of the bulge in S0 galaxies is 4.3×10^(10)M☉.We observe that SB0 galaxies show lower bulge concentration,low mass and also smaller B/T values compared to S0 galaxies.Using the Kormendy relation,we found that among the lenticular barred galaxies,82%have classical bulges and 18%have pseudo bulges.These classical bulges have low masses compared to the classical bulges of unbarred galaxies.S0,galaxies with massive classical bulges do not host bars.We also found that for all SB0s the bulge effective radius is less than the bar effective radius.SB0 galaxies with classical bulges suggest that the bar may have formed by mergers.
基金Supported by the National Natural Science Foundation of China
文摘We study the relationship between isophotal shapes, central light profiles and kinematic properties of early-type galaxies (ETGs) based on a compiled sample of 184 ETGs. These sample galaxies are included in Data Release 8 of the Sloan Digital Sky Survey and have central light profiles and kinematic properties available from the literature, which were compiled from observations by the Hubble Space Telescope and the ATLAS3D integral-field spectrograph, respectively. We find that there is only a weak correlation between the isophotal shape (a4/a) and the central light profile (within 1 kpc) of ETGs. About two-fifths of "core" galaxies have disky isophotes, and one-third of "power-law" galaxies are boxy. Our statistical results also show that there are weak correlations between galaxy luminosity and dynamical mass with a4/a, but such correlations are tighter with a central light profile. Moreover, no clear link has been found between the isophotal shape and the Sersic index. Comparisons show that there are similar correlations between a4/a and ellipticity, and between a4/a and specific angular momentum ARo/2 for "power-law" ETGs, but there are no such correlations for "core" ETGs. Therefore, we speculate that the bimodal classifications of ETGs are not as simple as previously thought, though we also find that the disky ETGs with highest a4/a are more elongated and fast rotators.
基金funded by the National Natural Science Foundation of China (NSFC) (Grant Nos. 10778618 and 10633020)the National Basic Research Program of China (973 Program) (Grant No. 2007CB815403)
文摘An optical photometric observation with the Beijing-Arizona-Taiwan- Connecticut (BATC) multicolor system is carried out for A98 (z =0.104), a galaxy cluster with two large enhancements in X-ray surface brightness. Spectral energy distributions (SEDs) covering 15 intermediate bands are obtained for all sources detected down to V - 20 mag in a field of 58′× 58′. After star-galaxy separation with colorcolor diagrams, a photometric redshift technique is applied to the galaxy sample for further membership determination. The color-magnitude relation is taken as a further restriction of the early-type cluster galaxies. As a result, a list of 198 faint member galaxies is achieved. Based on the newly generated sample of member galaxies, the dynamical substructures, A98N, A98S, and A98W, are investigated in detail. A separate galaxy group, A98X, is also found to the south of the main concentration of A98, which is gravitationally unbound to A98. For 74 spectroscopically confirmed member galaxies, the environmental effect on the star formation history is investigated. The bright galaxies in the core region are found to have shorter time scales of star formation, longer mean stellar ages, and higher interstellar medium metallicities, which can be interpreted in the context of the hierarchical cosmological scenario.
基金Supported by the National Natural Science Foundation of China.
文摘From photometric observations and star counts, the existence of a bar in the central few kpc of the Galaxy is suggested. It is generally thought that our Galaxy is surrounded by a massive invisible halo. The gravitational potential of the Galaxy is therefore made nonaxisymmetric generated by the central triaxial bar, by the outer triaxial halo, and/or by the spiral structures. Selecting nearly 300 open clusters with complete spatial velocity measurements and ages, we were able to construct the rotation curve of the Milky Way within a range of 3 kpc of the Sun. Using a dynamic model for an assumed elliptical disk, a clear weak elliptical potential of the disk with ellipticity of ε(R0) = 0.060 4± 0.012 is detected, the Sun is found to be near the minor axis, displaced by 30°±3°. The motion of the clusters is suggested to be on an oval orbit rather than on a circular one.
文摘By using the Mixture Model and radial velocity data from CfA redshift catalogue, we resolve the substructures of the Virgo cluster. Distances of three main subclusters are determined by the Tully-Fisher galaxies, they are 18.0±1.3Mpc, 25.0±2 3Mpc and 30.9±3.1Mpc respectively, which implicate that they are independent clusters, and the Virgo area has a significant depth in the line-of -sight direction.
基金supported in part by the Ministry of Science and Technology, Taiwan, under Li-Chin Yeh’s Grant MOST 106-2115-M-007-014Ing-Guey Jiang’s Grant MOST 106-2112-M-007-006-MY3
文摘An investigation on the possible dynamical models of the core galaxy NGC 1399 is performed.Because early-type galaxies are likely to be formed through merging events, remnant rings are considered in the modeling process.A numerical survey over three parameters is employed to obtain the best-fit models that are completely consistent with observations.It is found that the inner slope of the dark matter profile is cuspy for this core galaxy.The existence of remnant rings in best-fit models indicates a merging history.The remnant ring explains the flattened surface brightness and thus could be the physical counterpart of the core structure of NGC 1399.
基金partly supported by the National Key Research and Development Program of China(No.2018YFA0404501)the National Natural Science Foundation of China(Grant Nos.11821303,11761131004 and 11761141012)。
文摘We study the dynamical states of the 30 most massive galaxy clusters in the TNG100 simulation at redshift z = 0 using three types of tracers: stars, dark matter particles and satellite galaxies. If the massive galaxy cluster is spherically symmetric and relaxed, we can obtain the underlying total mass distribution accurately from its dynamical tracers using the spherical Jeans equations. Although the three tracers of clusters have very different number densities, velocity dispersions and anisotropies, they still trace the same total mass profile. We obtain the total mass profiles of clusters using these tracers separately and compare them with the true mass distributions. We find that:(1) the kinematics of dark matter trace the total mass of all clusters well and the mass inferred from dark matter are generally consistent with the true mass profiles with relative deviations smaller than ~ 25% at all radii;(2) stars in ~ 60% massive clusters are approaching equilibrium and the total mass of these clusters inferred from stars have relative deviations smaller than ~50% at all radii. Stellar substructures are rich and the mass inferred from stars tend to be over-estimated in the inner region;and(3) satellite galaxies are unrelaxed in the inner region and become more relaxed as the radius increases. The total mass inferred from satellites are under-estimated in all regions.
基金the National Natural Science Foundation of China.
文摘Convincing evidence for a past interaction between the two rich clusters A399 and A401 was recently found in the X-ray imaging observations. We examine the structure and dynamics of this pair of galaxy clusters. A mixture-modeling algorithm was applied to obtain a robust partition into two clusters, which allowed us to discuss the virial mass and velocity distribution of each cluster. Assuming that these two clusters follow a linear orbit and they have once experienced a close encounter, we model the binary cluster as a two-body system. As a result, four gravitationally bound solutions are obtained. The recent X-ray observations seem to favor a scenario in which the two clusters with a true separation of 5.4h-1 Mpc are currently expanding at 583 km s-1 along a direction with a projection angle of 67.5°, and they will reach a maximum extent of 5.65 h-1 Mpc in about 1.0 h-1 Gyr.
文摘We review the long-term survival chances of young massive star clusters (YMCs), hallmarks of intense starburst episodes often associated with Violent galaxy interactions. We address the key question as to whether at least some of these YMCs can be considered protoglobular clusters (GCs), in which case these would be expected to evolve into counterparts of the ubiquitous old GCs believed to be among the oldest galactic building blocks. In the absence of significant external perturbations, the key factor determining a cluster's long-term survival chances is the shape of its stellar initial mass function (IMF). It is, however, not straightforward to assess the IMF shape in unresolved extragalactic YMCs. We discuss in detail the promise of using high-resolution spectroscopy to make progress towards this goal, as well as the numerous pitfalls associated with this approach. We also discuss the latest progress in worldwide efforts to better understand the evolution of entire cluster systems, the disruption processes they are affected by, and whether we can use recently gained insights to determine the nature of at least some of the YMCs observed in extragalactic starbursts as proto-GCs. We conclude that there is an increasing body of evidence that GC formation appears to be continuing until today; their long-term evolution crucially depends on their environmental conditions, however.
文摘A cosmological model was developed using the equation of state of photon gas, as well as cosmic time. The primary objective of this model is to see if determining the observed rotation speed of galactic matter is possible, without using dark matter (halo) as a parameter. To do so, a numerical application of the evolution of variables in accordance with cosmic time and a new state equation was developed to determine precise, realistic values for a number of cosmological parameters, such as energy of the universe <i>U</i>, cosmological constant <i>E</i><sub>Λ</sub>, curvature of space <i>k</i>, energy density <i>ρ</i><sub>Λ<i>e</i></sub>, age of the universe <i>t</i><sub>Ω</sub> (part 1). That energy of the universe, when taken into consideration during the formation of the first galaxies (<1 [Gy]), provides a relatively adequate explanation of the non-Keplerian rotation of galactic masses (part 2). Indeed, such residual, non-baryonic energy, when considered in Newton’s gravity equation, adds the term <i>F</i><sub>Λ</sub>(<i>r</i>), which can partially explain, without recourse to dark matter, the rotations of some galaxies, such as M33, UGC12591, UGC2885, NGC3198, NGC253, DDO161, UDG44, the MW and the Coma cluster. Today, in the MW, that cosmological gravity force is in the order of 10<sup>26</sup> times smaller than the conventional gravity force. The model predicts an acceleration of the mass in the universe (<i>q</i>~-0.986);the energy associated with curvature <i>E<sub>k</sub></i> is the driving force behind the expansion of the universe, rather than the energy associated with the cosmological constant <i>E</i><sub>Λ</sub>. An equation to determine expansion is obtained using the energy form of the Friedmann equation relative to Planck power <i>P<sub>P</sub></i> and cosmic time or Planck force <i>F<sub>P</sub></i> acting at the frontier of the universe moving at <i>c</i>. This constant Planck force, from unknown sources, acts everywhere to the expansion of the universe as a stretching effect on the volume. Finally, the model partly explains the value a<sub>0</sub> of the MOND theory. Indeed, <i>a</i><sub>0</sub> is not a true constant, but depends on the cosmological constant at the time the great structures were formed (~1 [Gy]), as well as an adjustment of the typical mass and dimension of those great structures, such as galaxies. The constant a<sub>0</sub> is a different expression of the cosmological gravity force <i>F</i><sub>Λ</sub> as expressed by the cosmological constant, Λ, acting through the energy-mass equivalent during the formation of the structures. It does not put in question the value of <i>G</i>.
基金funded by the National Natural Science Foundation of China(NSFC)Grant No.11933011the Key Laboratory for Radio Astronomy+2 种基金support from the Natural Science Foundation of Jiangsu Province(grant number BK20210999)the Entrepreneurship and Innovation Program of Jiangsu ProvinceNSFC grant No.12203104。
文摘Open clusters(OCs)are infrequent survivors of embedded clusters gestated in molecular clouds.Up to now,little is known about the initial conditions for the formation of OCs.Here,we studied this issue using high-precision astrometric parameters provided by Gaia data release 3.The statistics show that the peculiar motion velocities of OCs vary slightly from infancy to old age,providing a remarkable opportunity to use OCs to trace their progenitors.Adopting a dynamical method,we derived the masses of the progenitor clumps where OCs were born,which have statistical characteristics comparable to previously known results for clumps observed in the Galaxy.Moreover,the masses of the progenitor clumps of OCs indicate they should be capable of gestating massive O-type stars.In fact,after inspecting the observed OCs and O-type stars,we found that there are many O-type stars in OCs.The destructive stellar feedback from O-type stars may disintegrate the vast majority of embedded clusters,and only those sufficiently dense ones can survive as OCs.
基金supported by grants from the Ministry of Science and Technology(MOST),Taiwan(MOST 105-2811-M-007-038,MOST 105-2119-M-007-029-MY3,MOST 106-2112-M-007-006-MY3 and MOST 106-2811-M-007-051)
文摘The kinematical parameters,spatial shape and structure of the open cluster IC 2391 and the associated stellar stream are studied here using Gaia Data Release 2(GDR2) astrometry data.The apex positions are determined for the open cluster IC 2391(data taken from Cantat-Gaudin et al.) and for the kinematical stream’s stars mentioned in Montes et al.employing both convergent point and AD-diagram methods.The values of apex coordinates are:(A,D)CP=(6.~h17 ± 0.~h004,-6.°88 ± 0.°381;for cluster) and(6.~h07 ± 0.~h007,-5.°00 ± 0.°447;stream),and(A0,D0) =(6.~h12 ± 0.~h004,-3.°4 ± 0.°3;cluster) and(6.~h21 ±0.~h007,-11.°895 ± 0.°290;stream).The results are in good agreement with the previously calculated values.The positions of the stars in the disk and the spatial dispersion velocities are determined.The paths of cluster and associated stream are traced in the disk by orbit calculation back in time to their places of formation.A possible genetic relationship between the cluster and stream has been detected.The approximation of the spatial and kinematical shape of the stream and the cluster is made.According to this study,even though currently the cluster and stream seem to have a spatial difference in their locations,they appear to have formed in the same region of the Galactic disk.
基金the National Key Research and Development Program of China(No.2017YFA0402701)the National Natural Science Foundation of China(Grant Nos.11988101,11933011,11833009)support from the Youth Innovation Promotion Association,CAS。
文摘The age pattern across spiral arms is one of the key observational features utilised to study the dynamic nature of the Galaxy’s spiral structure.With the most updated samples of high-mass star formation region(HMSFR)masers,O stars and open clusters,we investigated their distributions and kinematic properties in the vicinity of the Sun.We found that the Sagittarius-Carina Arm traced by HMSFRs,O stars((?)10 Myr)and young open clusters(<30 Myr)seem to deviate gradually towards the Galactic Anticenter(GAC)direction.The Local Arm traced by HMSFRs,O stars,young clusters and also mediumyoung clusters(30-100 Myr)are inclined to gradually deviate toward the Galactic Center(GC)direction.The properties for the Local Arm are supported by a simplified simulation of cluster motions in the Galaxy.Indications of systematic motions in the circular and radial velocities are noticed for the old open clusters(>200 Myr).These results are consistent with the idea that star formation can be triggered by spiral shocks of density waves,and indicate that the corotation radius of the Galaxy is located between the SagittariusCarina Arm and the Local Arm,close to the Solar circle.
文摘Fitting parametric models to globular clusters’structural profiles has been essential for the study of stellar dynamics.It provides their important structural parameters,such as the concentrations and core radii of the clusters.However,existing parametric models can apply only to non-collapsing-core clusters in the early relaxation-evolution stage.Hence,a single parametric model cannot provide globular clusters’structural parameters in both the early and late evolution stages.We have recently found an accurate spectral solution for the self-similar orbit-averaged Fokker-Planck(OAFP)equation to model collapsingcore clusters at the late evolution stage.The present work establishes a new parametric model by combining the self-similar OAFP-and polytropic-models.Although it is a single-mass and isotropic model,the new model applies to at least fifty-five Galactic globular clusters with resolved cores in all the evolution stages.As a main result,we show the characteristics of the relaxation times against the concentrations of the clusters.We also affirm that the structures of low-concentration clusters are polytropic in the Milky Way.
基金Supported by the National Natural Science Foundation of China.
文摘We present a new determination of the Galactocentric distance by a pure kinematical model. Two subgroups of components from the Galactic thin disk, the O-B5 stars and the Galactic open clusters, were selected for our analysis. On the basis of kinematical data of around 1200 O-B5 stars, we obtained an estimated value of Ro=8.25-4-0.79 kpc, while a similar evaluation from 270 Galactic open clusters gives Ro=7.95-4-0.62 kpc. Considering the scatter of Ro given by individual investigators with different methods, our present determinations agree well with the best value proposed by Reid.
基金Supported by the National Natural Science Foundation of China.
文摘Absolute proper motions and radial velocities of 202 open clusters in the solar neighborhood, which can be used as tracers of the Galactic disk, are used to investigate the kinematics of the Galaxy in the solar vicinity, including the mean heliocentric velocity components (u1, u2, u3) of the open cluster system, the characteristic velocity dispersions (σ1,σ2,σ3), Oort constants (A, B) and the large-scale radial motion parameters (C, D) of the Galaxy. The results derived from the observational data of proper motions and radial velocities of a subgroup of 117 thin disk young open clusters by means of a maximum likelihood algorithm are: (u1,u2,u3) = (-16.1 ± 1.0,-7.9 ±1.4,-10.4±1.5) km·s^-1, (σ1,σ2,σ3) = (17.0±0.7, 12.2±0.9, 8.0±1.3) km·S^-1, (A, B) = (14.8±1.0, - 13.0±2.7) km·s^-1 kpc^-1, and (C, D) = (1.5 ± 0.7, -1.2 ±1.5) km·s^-1 kpc^-1. A discussion on the results and comparisons with what was obtained by other authors is given.
基金supported by the National Natural Science Foundation of China(NSFC,Grant No.11403004)the School Foundation of Changzhou University(ZMF1002121)+3 种基金support by the 973 Program(2014CB845702)the Strategic Priority Research Program The Emergence of Cosmological Structures of the Chinese Academy of Sciences(CASgrant XDB09010100)by the NSFC(No.11373054)
文摘Abstract We report the discovery of 45 high-velocity extreme horizontal branch (EHB) stars in the globular cluster Omega Centauri (NGC 5139). The tangential ve- locities of these EHB stars are determined to be in the range 93-313 km s^-1, with an average uncertainty of -27 km s^-1. The central escape velocity of the cluster is determined to be in the range 60~105 km s^-1. These EHB stars are significantly more concentrated toward the cluster core compared with other cluster members. The formation mechanisms of these EHB stars are discussed. Our conclusions can be sum- marized as follows: (1) A comparison of the tangential velocities of these EHB stars to the central escape velocity of the cluster shows that most if not all of these EHB stars are unbound to the cluster; (2) These EHB stars obtained high velocities in the central cluster region no longer than - 1 Myr ago and may be subsequently ejected from the cluster in the next -1 Myr; (3) If the progenitors of these EHB stars were single stars, then they may have experienced a fast mass-loss process. If the progen- itors were in close binaries, then they may have formed through disruptions by the intermediate-mass black hole in the cluster center.
基金funded by the National Natural Science Foundation of China (Grant Nos. 11173016, 10873016, 11073032, 11003021 and 10803007)the National Basic Research Program of China (973 Program Grant No. 2007CB815403)
文摘This paper presents multicolor optical photometry of the nearby galaxy cluster Abell 119 (z = 0.0442) with the Beijing-Arizona-Taiwan-Connecticut system of 15 intermediate bands. Within the BATC field of view of 58'× 58', there are 368 galaxies with known spectroscopic redshifts, including 238 member galaxies (called sample I). Based on the spectral energy distributions of 1376 galaxies brighter than iBATC ---- 19.5, the photometric redshift technique and the color-magnitude relation of early-type galaxies are applied to select faint member galaxies. As a result, 117 faint galaxies were selected as new member galaxies. Combined with sample I, an enlarged sample (called sample II) of 355 member galaxies is obtained. Spatial distribution and localized velocity structure for two samples demonstrate that A119 is a dynami- cally complex cluster with at least three prominent substructures in the central region within 1 Mpc. A large velocity dispersion for the central clump indicates a merging along the line of sight. No significant evidence for morphology or luminosity segrega- tions is found in either sample. With the PEGASE evolutionary synthesis model, the environmental effect on the properties of star formation is confirmed. Faint galaxies in the low-density region tend to have longer time scales of star formation, smaller mean stellar ages, and lower metallicities in their interstellar medium, which is in agreement with the context of the hierarchical cosmological scenario.