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 structural and dynamical properties of A209 based on Chandra and XMM-Newton observations.We obtain detailed temperature,pressure,and entropy maps with the contour binning method,and find a hot region in t...We study the structural and dynamical properties of A209 based on Chandra and XMM-Newton observations.We obtain detailed temperature,pressure,and entropy maps with the contour binning method,and find a hot region in the NW direction.The X-ray brightness residual map and corresponding temperature profiles reveal a possible shock front in the NW direction and a cold front feature in the SE direction.Combined with the galaxy luminosity density map we propose a weak merger scenario.A young sub-cluster passing from the SE to NW direction could explain the optical subpeak,the intracluster medium temperature map,the X-ray surface brightness excess,and the X-ray peak offset together.展开更多
Open clusters(OCs) are common in the Milky Way, but most of them remain undiscovered. There are numerous techniques, including some machine-learning algorithms, available for the exploration of OCs. However, each meth...Open clusters(OCs) are common in the Milky Way, but most of them remain undiscovered. There are numerous techniques, including some machine-learning algorithms, available for the exploration of OCs. However, each method has its limitations and therefore, different approaches to discovering OCs hold significant values. We develop a comprehensive approach method to automatically explore the data space and identify potential OC candidates with relatively reliable membership determination. This approach combines the techniques of Hierarchical Density-Based Spatial Clustering of Applications with Noise, Gaussian mixture model, and a novel cluster member identification technique, color excess constraint. The new method exhibits efficiency in detecting OCs while ensuring precise determination of cluster memberships. Because the main feature of this technique is to add an extra constraint(EC) for the members of cluster candidates using the homogeneity of color excess,compared to typical blind search codes, it is called Blind Search-Extra Constraint(BSEC) method. It is successfully applied to the Gaia Data Release 3, and 83 new OCs are found, whose color–magnitude diagrams(CMDs) are fitted well to the isochrones. In addition, this study reports 621 new OC candidates with discernible main sequence or red giant branch. It is shown that BSEC technique can discard some false negatives of previous works, which takes about three percentage of known clusters. It shows that as an EC, the color excess(or twocolor) constraint is useful for removing fake cluster member stars from the clusters that are identified from the positions and proper motions of stars, and getting more precise CMDs, when differential reddening of member stars of a cluster is not large(e.g., ΔE(G_(BP)-G_(RP)) < 0.5 mag). It makes the CMDs of 15% clusters clearer(in particular for the region near turnoff) and therefore is helpful for CMD and stellar population studies. Our result suggests that the color excess constraint is more appropriate for clusters with small differential reddening, such as globular clusters or older OCs, and clusters that the distances of member stars cannot be determined accurately.展开更多
Using archival Fermi-LAT data with a time span of~12 yr,we study the population of Millisecond Pulsars(MSPs)in Globular Clusters(GlCs)and investigate their dependence on cluster dynamical evolution in the Milky Way.We...Using archival Fermi-LAT data with a time span of~12 yr,we study the population of Millisecond Pulsars(MSPs)in Globular Clusters(GlCs)and investigate their dependence on cluster dynamical evolution in the Milky Way.We show that theγ-ray luminosity(L_(γ))and emissivity(i.e.,ε_(γ)=L_(γ)/M,with M the cluster mass)are good indicators of the population and abundance of MSPs in GlCs,and they are highly dependent on the dynamical evolution history of the host clusters.Specifically speaking,the dynamically older GlCs with more compact structures are more likely to have larger L_(γ)andε_(γ),and these trends can be summarized as strong correlations with cluster stellar encounter rateΓand the specific encounter rate(Λ=Γ/M),with L_(γ)∝Γ^(0.7±0.11)andε_(γ)∝Λ^(0.73±0.13)for dynamically normal GlCs.However,as GlCs evolve into deep core collapse,these trends are found to be reversed,implying that strong encounters may have lead to the disruption of Low-Mass X-ray Binaries and ejection of MSPs from core-collapsed systems.Besides,the GlCs are found to exhibit largerε_(γ)with increasing stellar mass function slope(ε_(γ)∝10^((0.52±0.1)α)),decreasing tidal radius(ε_(γ)∝R_(t)^(-10±0.22))and distances from the Galactic Center(GC,ε_(γ)∝R_(gc)^(-1.13±0.21)).These correlations indicate that,as GlCs losing kinetic energy and spiral in toward the GC,tidal stripping and mass segregation have a preference in leading to the loss of normal stars from GlCs,while MSPs are more likely to concentrate to cluster center and be deposited into the GC.Moreover,we gaugeε_(γ)of GlCs is~10-1000 times larger than the Galactic bulge,the latter is thought to reside thousands of unresolved MSPs and may be responsible for the GC 7-ray excess,which supports that GlCs are generous contributors to the population of MSPs in the GC.展开更多
We fit various color–magnitude diagrams(CMDs) of the high-latitude Galactic globular clusters NGC 5024(M53),NGC 5053,NGC 5272(M3),NGC 5466,and NGC 7099(M30) by isochrones from the Dartmouth Stellar Evolution Database...We fit various color–magnitude diagrams(CMDs) of the high-latitude Galactic globular clusters NGC 5024(M53),NGC 5053,NGC 5272(M3),NGC 5466,and NGC 7099(M30) by isochrones from the Dartmouth Stellar Evolution Database and Bag of Stellar Tracks and Isochrones for α–enrichment [α/Fe] = +0.4.For the CMDs,we use data sets from Hubble Space Telescope,Gaia,and other sources utilizing,at least,25 photometric filters for each cluster.We obtain the following characteristics with their statistical uncertainties for NGC 5024,NGC 5053,NGC 5272,NGC 5466,and NGC 7099,respectively:metallicities [Fe/H] =-1.93 ± 0.02,-2.08 ± 0.03,-1.60 ± 0.02,-1.95 ± 0.02,and-2.07 ± 0.04 dex with their systematic uncertainty 0.1 dex;ages 13.00 ± 0.11,12.70 ± 0.11,11.63 ± 0.07,12.15 ± 0.11,and 12.80 ± 0.17 Gyr with their systematic uncertainty 0.8 Gyr;distances(systematic uncertainty added) 18.22 ± 0.06 ± 0.60,16.99 ± 0.06 ± 0.56,10.08 ± 0.04 ± 0.33,15.59 ±0.03 ± 0.51,and 8.29 ± 0.03 ± 0.27 kpc;reddenings E(B-V) = 0.023 ± 0.004,0.017 ± 0.004,0.023 ± 0.004,0.023 ± 0.003,and 0.045 ± 0.002 mag with their systematic uncertainty 0.01 mag;extinctions AV= 0.08 ± 0.01,0.06 ± 0.01,0.08 ± 0.01,0.08 ± 0.01,and 0.16 ± 0.01 mag with their systematic uncertainty 0.03 mag,which suggest the total Galactic extinction AV= 0.08 across the whole Galactic dust to extragalactic objects at the North Galactic Pole.The horizontal branch morphology difference of these clusters is explained by their different metallicity,age,mass-loss efficiency,and loss of low-mass members in the evolution of the core-collapse cluster NGC 7099 and loose clusters NGC 5053 and NGC 5466.展开更多
Open clusters are the basic building blocks that serve as a laboratory for the study of young stellar populations in the Milky Way.Variable stars in open clusters provide a unique way to accurately probe the internal ...Open clusters are the basic building blocks that serve as a laboratory for the study of young stellar populations in the Milky Way.Variable stars in open clusters provide a unique way to accurately probe the internal structure,temporal and dynamical evolutionary stages of individual stars and the host cluster.The most powerful tool for such studies is time-domain photometric observations.This paper follows the route of our previous work,concentrating on a photometric search for variable stars in NGC 884.The target cluster is the companion of NGC869,forming the well-known double cluster system that is gravitationally bound.From the observation run in 2016 November,a total of 9247 B-band CCD images and 8218Ⅴ-band CCD images were obtained.We detected a total of 15 stars with variability in visual brightness,including five Be stars,three eclipsing binaries,and seven of unknown types.Two new variable stars were discovered in this work.We also compared the variable star content of NGC 884 with its companion NGC 869.展开更多
Recent studies indicate that some Galactic open clusters(OCs)exhibit extended main-sequence turnoff(eMSTO)in their color–magnitude diagrams(CMDs).However,the number of Galactic OCs with eMSTO structures detected so f...Recent studies indicate that some Galactic open clusters(OCs)exhibit extended main-sequence turnoff(eMSTO)in their color–magnitude diagrams(CMDs).However,the number of Galactic OCs with eMSTO structures detected so far is limited,and the reasons for their formation are still unclear.This work identifies 26 Galactic OCs with undiscovered eMSTOs and investigates the causes of these features.Stellar population types and fundamental parameters of cluster samples are acquired using CMD fitting methods.Among them,the results of 11 OCs are reliable as the observed CMDs are well-reproduced.We propose the crucial role of stellar binarity and confirm the importance of stellar rotation in reproducing eMSTO morphologies.The results also show that the impact of age spread is important,as it can adequately explain the structure of young OCs and fit the observed CMDs of intermediate-age OCs better.展开更多
Recently, a new radio millisecond pulsar(MSP) J1740-5340B, hosted in the globular cluster(GC) NGC 6397,was reported with a 5.78 ms spin period in an eclipsing binary system with a 1.97 days orbital period. Based on a ...Recently, a new radio millisecond pulsar(MSP) J1740-5340B, hosted in the globular cluster(GC) NGC 6397,was reported with a 5.78 ms spin period in an eclipsing binary system with a 1.97 days orbital period. Based on a modified radio ephemeris updated by tool tempo2, we analyze the ~15 yr γ-ray data obtained from the Large Area Telescope on board the Fermi Gamma-ray Space Telescope and detect PSR J1740-5340B's γ-ray pulsation at a confidence level of ~4σ with a weighted H-test value of ~26. By performing a phase-resolved analysis, the γ-ray luminosity in on-pulse interval of PSR J1740-5340B is L_(γ)~ 3.8 × 10^(33) erg s^(-1) using NGC 6397's distance of 2.48 kpc. And γ-rays from the on-pulse part of PSR J1740-5340B contribute ~90% of the total observed γ-ray emissions from NGC 6397. No significant γ-ray pulsation of another MSP J1740-5340A in the GC is detected.Considering that the previous four cases of MSPs in GCs, more data in γ-ray, X-ray, and radio are encouraged to finally confirm the γ-ray emissions from MSP J1740-5340B, especially starving for a precise ephemeris.展开更多
This paper develops the Dark Matter by Quantum Gravitation theory, DMbQG theory hereafter, in clusters of galaxies in the cosmologic model ΛCDM of the Universe. Originally this theory was developed by the author for ...This paper develops the Dark Matter by Quantum Gravitation theory, DMbQG theory hereafter, in clusters of galaxies in the cosmologic model ΛCDM of the Universe. Originally this theory was developed by the author for galaxies, especially using MW and M31 rotation curves. An important result got by the DMbQG theory is that the total mass associated to a galactic halo depend on the square root of radius, being its dominion unbounded. Apparently, this result would be absurd because of divergence of the total mass. As the DE is negligible at galactic scale, it is needed to extend the theory to clusters in order to study the capacity of DE to counterbalance to DM. Thanks this property, the DMbQG theory finds unexpected theoretical results. In this work, it is defined, the total mass as baryonic matter plus DM and the gravitating mass as the addition of the total mass plus the negative mass associated to dark energy. In clusters it is defined the zero gravity radius (RZG hereafter) as the radius needed by the dark energy to counterbalance the total mass. It has been found that the ratio RZG/RVIRIAL ≈ 7.3 and its Total mass associated at RZG is ≈2.7 MVIRIAL. In addition, it has been calculated that the sphere with the extended halo radius RE = 1.85 RZG has a ratio DM density versus DE density equal to 3/7 and its total mass associated at RE is ≈3.6 MVIRIAL. This works postulates that the factor 3.6 may equilibrate perfectly the strong imbalance between the Local mater density parameter (0.08) versus the current Global matter density one (0.3). Currently, this fact is a big conundrum in cosmology, see chapter 7. Also it has been found that the zero velocity radius, RZV hereafter, i.e. the cluster border because of the Hubble flow, is ≈0.6 RZG and its gravitating mass is ≈ 1.5 MVIR. By derivation of gravitating mass function, it is calculated that at 0.49 RZG, this function reaches its maximum whose value is ≈1.57 MVIR. Throughout the paper, some of these results have been validated with recent data published for the Virgo cluster. As Virgo is the nearest big cluster, it is the perfect benchmark to validate any new theory about DM and DE. These new theoretical findings offer to scientific community a wide number of tests to validate or reject the theory. The validation of DMbQG theory would mean to know the nature of DM that at the present, it is an important challenge for the astrophysics science.展开更多
We develop a theoretical formulation for the large-scale dynamics of galaxy clusters involving two spherical 'isothermal fluids' coupled by their mutual gravity and derive asymptotic similarity solutions analy...We develop a theoretical formulation for the large-scale dynamics of galaxy clusters involving two spherical 'isothermal fluids' coupled by their mutual gravity and derive asymptotic similarity solutions analytically. One of the fluids roughly approximates the massive dark matter halo, while the other describes the hot gas, the relatively small mass contribution from the galaxies being subsumed in the gas. By properly choosing the self-similar variables, it is possible to consistently transform the set of time-dependent two-fluid equations of spherical symmetry with self-gravity into a set of coupled nonlinear ordinary differential equations (ODEs). We focus on the analytical analysis and discuss applications of the solutions to galaxy clusters.展开更多
Clusters of galaxies are the most massive objects in the Universe and precise knowledge of their mass structure is important to understand the history of structure formation and constrain still unknown types of dark c...Clusters of galaxies are the most massive objects in the Universe and precise knowledge of their mass structure is important to understand the history of structure formation and constrain still unknown types of dark contents of the Universe. X-ray spectroscopy of galaxy clusters provides rich information about the physical state of hot intracluster gas and the underlying potential structure. In this paper, starting from the basic description of clusters under equilibrium conditions, we review properties of clusters revealed primarily through X-ray observations considering their thermal and dynamical evolutions. The future prospects of cluster studies using upcoming X-ray missions are also mentioned.展开更多
We present an analysis of the winding sense(S and Z-shapes) of 1 621 field galaxies that have radial velocity between 3 000 km s-1 and 5 000 km s-1.The preferred alignments of S-and Z-shaped galaxies are studied usi...We present an analysis of the winding sense(S and Z-shapes) of 1 621 field galaxies that have radial velocity between 3 000 km s-1 and 5 000 km s-1.The preferred alignments of S-and Z-shaped galaxies are studied using chi-square,autocorrelation and Fourier series tests.We classify all the galaxies into 32 subsamples and notice a good agreement between the position angle(PA) distribution of the S-and Zshaped galaxies.The homogeneous distribution of the S-and Z-shaped galaxies is more noticeable for the late-type spirals(Sc,Scd,Sd and Sm) than for the early-types(Sa,Sab,Sb and Sbc) .A significant dominance of S-mode galaxies is apparent in the barred spirals.A random alignment is evident in the PA-distribution of Z-and S-mode spirals.In addition,a homogeneous distribution of the S-and Z-shaped galaxies is found to be invariant under global expansion.The PA-distribution of the total S-mode galaxies is found to be random,whereas a preferred alignment is clear for all the Zmode galaxies.It is found that the galactic planes of Z-mode galaxies tend to lie in the equatorial plane.展开更多
We create mock X-ray observations of hot gas in galaxy clusters with a new extension of the L-Galaxies semianalytic model of galaxy formation,which includes the radial distribution of hot gas in each halo.Based on the...We create mock X-ray observations of hot gas in galaxy clusters with a new extension of the L-Galaxies semianalytic model of galaxy formation,which includes the radial distribution of hot gas in each halo.Based on the model outputs,we first build some mock light cones,then generate mock spectra with the SOXS package and derive the mock images in the light cones.Using the mock data,we simulate mock X-ray spectra for the ROSAT all-sky survey,and compare the mock spectra with the observational results.Then,we consider the design parameters of the HUBS mission and simulate the observation of the halo hot gas for HUBS as an important application of our mock work.We find:(1)our mock data match the observations by current X-ray telescopes.(2)The survey of hot baryons in resolved clusters by HUBS is effective below redshift 0.5,and the observations of the emission lines in point-like sources at z>0.5 by HUBS help us understand the hot baryons in the early universe.(3)By taking advantage of the large simulation box and flexibility in semi-analytic models,our mock X-ray observations provide the opportunity to select targets and observation strategies for forthcoming X-ray facilities.展开更多
As groups of coeval stars born from the same molecular cloud,an open cluster(OC)is an ideal laboratory for studying the structure and dynamical evolution of the Milky Way.The release of high-precision Gaia Early Data ...As groups of coeval stars born from the same molecular cloud,an open cluster(OC)is an ideal laboratory for studying the structure and dynamical evolution of the Milky Way.The release of high-precision Gaia Early Data Release 3(Gaia EDR3)and modern machine-learning methods offer unprecedented opportunities to identify OCs.In this study,we extended conventional HDBSCAN(e-HDBSCAN)for searching for new OCs in Gaia EDR3.A pipeline was developed based on the parallel computing technique to blindly search for OCs from Gaia EDR3within Galactic latitudes∣b∣<25°.As a result,we obtained 3787 star clusters,of which 83 new OCs were reported after cross-match and visual inspection.At the same time,the main star cluster parameters are estimated by color-magnitude diagram fitting.The study significantly increases the sample size and physical parameters of OCs in the catalog of OCs.It shows the incompleteness of the census of OCs across our Galaxy.展开更多
We combine the kinematics of 159 globular clusters(GCs) provided by the Gaia Early Data Release 3(EDR3) with other observational data to classify the GCs,and to estimate the mass of the Milky Way(MW).We use the agemet...We combine the kinematics of 159 globular clusters(GCs) provided by the Gaia Early Data Release 3(EDR3) with other observational data to classify the GCs,and to estimate the mass of the Milky Way(MW).We use the agemetallicity relation,integrals of motion,action space and the GC orbits to identify the GCs as either formed in situ(Bulge and Disk) or ex situ(via accretion).We find that 45.3% have formed in situ,while 38.4% may be related to known merger events:Gaia-Sausage-Enceladus,the Sagittarius dwarf galaxy,the Helmi streams,the Sequoia galaxy and the Kraken galaxy.We also further identify three new sub-structures associated with the Gaia-Sausage-Enceladus.The remaining 16.3% of GCs are unrelated to the known mergers and thought to be from small accretion events.We select 46 GCs which have radii 8.0 <r<37.3 kpc and obtain the anisotropy parameter β=0.315_(-0.049)^(+0.055),which is lower than the recent result using the sample of GCs in Gaia Data Release 2,but still in agreement with it by considering the error bar.By using the same sample,we obtain the MW mass inside the outermost GC as M(<37.3 kpc)=0.423_(-0.02)^(+0.02)×10^(12)M_(⊙),and the corresponding M_(200)=1.11_(-0.18)^(+0.25)×10^(12)M_(⊙).The estimated mass is consistent with the results in many recent studies.We also find that the estimated β and mass depend on the selected sample of GCs.However,it is difficult to determine whether a GC fully traces the potential of the MW.展开更多
Up to 2022 November,267 pulsars had been discovered in 36 globular clusters(GCs).In this paper,we present our studies on the distribution of GC pulsar parameters and the detection efficiency.The power law relation bet...Up to 2022 November,267 pulsars had been discovered in 36 globular clusters(GCs).In this paper,we present our studies on the distribution of GC pulsar parameters and the detection efficiency.The power law relation between average dispersion measure(■)and dispersion measure difference(ΔDM)of known pulsars in GCs is lgΔDM∝1.52lg■.The sensitivity could be the key to finding more pulsars.As a result,several years after the construction of a large radio telescope facility,the number of known GC pulsars will likely be increased accordingly.We suggest that currently GCs in the southern hemisphere could have higher possibilities for finding new pulsars.展开更多
The binary population in field stars and star clusters contributes to the formation of gravitational wave(GW)sources.However,the fraction of compact-object binaries(CBs),which is an important feature parameter of bina...The binary population in field stars and star clusters contributes to the formation of gravitational wave(GW)sources.However,the fraction of compact-object binaries(CBs),which is an important feature parameter of binary populations,is still difficult to measure and very uncertain.This paper predicts the fractions of important CBs and semi-compact object binaries(SCBs) making use of an advanced stellar population synthesis technique.A comparison with the result of N-body simulation is also presented.It is found that most CBs are formed within about 500 Myr after the starburst.The fractions of CBs and SCBs are demonstrated to correlate with stellar metallicity.The higher the metallicity becomes,the smaller the fraction of black hole binaries(BHBs),neutron star binaries(NSBs) and SCBs.This suggests that the GW sources of BHBs and NSBs are more likely to form in metal-poor environments.However,the fraction of black hole-neutron star binaries is shown to be larger for metalrich populations on average.展开更多
The China Space Station Telescope(CSST)is a 2 m space-based optical-UV telescope.Its primary goal is to carry out a high-resolution photometric imaging survey of a 17,500 square degree sky area using the on board Surv...The China Space Station Telescope(CSST)is a 2 m space-based optical-UV telescope.Its primary goal is to carry out a high-resolution photometric imaging survey of a 17,500 square degree sky area using the on board Survey Camera.With its wide field of view(1.1 square degrees)and a mosaic imager containing 640 million pixels,studying the different populations of stars within star clusters is highly feasible.The aim of this study is to assess the CSST's ability to distinguish between stellar populations with varying helium abundance levels,with the help of Modules for Experiments in Stellar Astrophysics.The results of the CSST's photometry for these different populations are presented by transferring the models into the CSST Survey Camera photometric system.The findings confirm that helium-enriched stellar populations will have unique patterns in the color-magnitude diagrams under the CSST photometric system,compared to normal stellar populations.The CSST,with its filters and wide field of view of the Survey Camera,provides a new avenue for the study of multiple populations in star clusters.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
We revisit the γ-ray emission above 300 Me V towards the massive star-forming region of Orion B by adopting14 yr observations with the Fermi Large Area Telescope and utilizing the updated software tools.The extended ...We revisit the γ-ray emission above 300 Me V towards the massive star-forming region of Orion B by adopting14 yr observations with the Fermi Large Area Telescope and utilizing the updated software tools.The extended γ-ray emission region around Orion B is resolved into two components(region Ⅰ and region Ⅱ).The γ-ray spectrum of region I agrees with the predicted γ-ray spectrum assuming the cosmic ray(CR)density is the same as that of Alpha Magnetic Spectrometer(AMS-02)measured locally.Theγ-ray emissivity of region II appears to be deficit at low energy band(E<3 GeV).Through modeling we find that CR densities exhibit a significant deficit below 20 Ge V,which may be caused by a slow diffusion inside the dense region.This is probably caused by an increased magnetic field whose strength increases with the gas density.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(grant Nos.U2038104 and 11703014)the Bureau of International Cooperation,Chinese Academy of Sciences(GJHZ1864)。
文摘We study the structural and dynamical properties of A209 based on Chandra and XMM-Newton observations.We obtain detailed temperature,pressure,and entropy maps with the contour binning method,and find a hot region in the NW direction.The X-ray brightness residual map and corresponding temperature profiles reveal a possible shock front in the NW direction and a cold front feature in the SE direction.Combined with the galaxy luminosity density map we propose a weak merger scenario.A young sub-cluster passing from the SE to NW direction could explain the optical subpeak,the intracluster medium temperature map,the X-ray surface brightness excess,and the X-ray peak offset together.
基金supported by Yunnan Academician Workstation of Wang Jingxiu(202005AF150025)China Manned Space Project(NO.CMS-CSST-2021-A08)Guanghe project(ghfund202302019167)。
文摘Open clusters(OCs) are common in the Milky Way, but most of them remain undiscovered. There are numerous techniques, including some machine-learning algorithms, available for the exploration of OCs. However, each method has its limitations and therefore, different approaches to discovering OCs hold significant values. We develop a comprehensive approach method to automatically explore the data space and identify potential OC candidates with relatively reliable membership determination. This approach combines the techniques of Hierarchical Density-Based Spatial Clustering of Applications with Noise, Gaussian mixture model, and a novel cluster member identification technique, color excess constraint. The new method exhibits efficiency in detecting OCs while ensuring precise determination of cluster memberships. Because the main feature of this technique is to add an extra constraint(EC) for the members of cluster candidates using the homogeneity of color excess,compared to typical blind search codes, it is called Blind Search-Extra Constraint(BSEC) method. It is successfully applied to the Gaia Data Release 3, and 83 new OCs are found, whose color–magnitude diagrams(CMDs) are fitted well to the isochrones. In addition, this study reports 621 new OC candidates with discernible main sequence or red giant branch. It is shown that BSEC technique can discard some false negatives of previous works, which takes about three percentage of known clusters. It shows that as an EC, the color excess(or twocolor) constraint is useful for removing fake cluster member stars from the clusters that are identified from the positions and proper motions of stars, and getting more precise CMDs, when differential reddening of member stars of a cluster is not large(e.g., ΔE(G_(BP)-G_(RP)) < 0.5 mag). It makes the CMDs of 15% clusters clearer(in particular for the region near turnoff) and therefore is helpful for CMD and stellar population studies. Our result suggests that the color excess constraint is more appropriate for clusters with small differential reddening, such as globular clusters or older OCs, and clusters that the distances of member stars cannot be determined accurately.
基金supported by the Youth Program of the National Natural Science Foundation of China No.12003017。
文摘Using archival Fermi-LAT data with a time span of~12 yr,we study the population of Millisecond Pulsars(MSPs)in Globular Clusters(GlCs)and investigate their dependence on cluster dynamical evolution in the Milky Way.We show that theγ-ray luminosity(L_(γ))and emissivity(i.e.,ε_(γ)=L_(γ)/M,with M the cluster mass)are good indicators of the population and abundance of MSPs in GlCs,and they are highly dependent on the dynamical evolution history of the host clusters.Specifically speaking,the dynamically older GlCs with more compact structures are more likely to have larger L_(γ)andε_(γ),and these trends can be summarized as strong correlations with cluster stellar encounter rateΓand the specific encounter rate(Λ=Γ/M),with L_(γ)∝Γ^(0.7±0.11)andε_(γ)∝Λ^(0.73±0.13)for dynamically normal GlCs.However,as GlCs evolve into deep core collapse,these trends are found to be reversed,implying that strong encounters may have lead to the disruption of Low-Mass X-ray Binaries and ejection of MSPs from core-collapsed systems.Besides,the GlCs are found to exhibit largerε_(γ)with increasing stellar mass function slope(ε_(γ)∝10^((0.52±0.1)α)),decreasing tidal radius(ε_(γ)∝R_(t)^(-10±0.22))and distances from the Galactic Center(GC,ε_(γ)∝R_(gc)^(-1.13±0.21)).These correlations indicate that,as GlCs losing kinetic energy and spiral in toward the GC,tidal stripping and mass segregation have a preference in leading to the loss of normal stars from GlCs,while MSPs are more likely to concentrate to cluster center and be deposited into the GC.Moreover,we gaugeε_(γ)of GlCs is~10-1000 times larger than the Galactic bulge,the latter is thought to reside thousands of unresolved MSPs and may be responsible for the GC 7-ray excess,which supports that GlCs are generous contributors to the population of MSPs in the GC.
基金financial support from the Russian Science Foundation (grant No.20-72-10052)。
文摘We fit various color–magnitude diagrams(CMDs) of the high-latitude Galactic globular clusters NGC 5024(M53),NGC 5053,NGC 5272(M3),NGC 5466,and NGC 7099(M30) by isochrones from the Dartmouth Stellar Evolution Database and Bag of Stellar Tracks and Isochrones for α–enrichment [α/Fe] = +0.4.For the CMDs,we use data sets from Hubble Space Telescope,Gaia,and other sources utilizing,at least,25 photometric filters for each cluster.We obtain the following characteristics with their statistical uncertainties for NGC 5024,NGC 5053,NGC 5272,NGC 5466,and NGC 7099,respectively:metallicities [Fe/H] =-1.93 ± 0.02,-2.08 ± 0.03,-1.60 ± 0.02,-1.95 ± 0.02,and-2.07 ± 0.04 dex with their systematic uncertainty 0.1 dex;ages 13.00 ± 0.11,12.70 ± 0.11,11.63 ± 0.07,12.15 ± 0.11,and 12.80 ± 0.17 Gyr with their systematic uncertainty 0.8 Gyr;distances(systematic uncertainty added) 18.22 ± 0.06 ± 0.60,16.99 ± 0.06 ± 0.56,10.08 ± 0.04 ± 0.33,15.59 ±0.03 ± 0.51,and 8.29 ± 0.03 ± 0.27 kpc;reddenings E(B-V) = 0.023 ± 0.004,0.017 ± 0.004,0.023 ± 0.004,0.023 ± 0.003,and 0.045 ± 0.002 mag with their systematic uncertainty 0.01 mag;extinctions AV= 0.08 ± 0.01,0.06 ± 0.01,0.08 ± 0.01,0.08 ± 0.01,and 0.16 ± 0.01 mag with their systematic uncertainty 0.03 mag,which suggest the total Galactic extinction AV= 0.08 across the whole Galactic dust to extragalactic objects at the North Galactic Pole.The horizontal branch morphology difference of these clusters is explained by their different metallicity,age,mass-loss efficiency,and loss of low-mass members in the evolution of the core-collapse cluster NGC 7099 and loose clusters NGC 5053 and NGC 5466.
基金the National Natural Science Foundation of China(NSFC)through grants 12003022,12373035,12233009 and 12173047support from the Youth Innovation Promotion Association of the CAS(grant No.2022055)。
文摘Open clusters are the basic building blocks that serve as a laboratory for the study of young stellar populations in the Milky Way.Variable stars in open clusters provide a unique way to accurately probe the internal structure,temporal and dynamical evolutionary stages of individual stars and the host cluster.The most powerful tool for such studies is time-domain photometric observations.This paper follows the route of our previous work,concentrating on a photometric search for variable stars in NGC 884.The target cluster is the companion of NGC869,forming the well-known double cluster system that is gravitationally bound.From the observation run in 2016 November,a total of 9247 B-band CCD images and 8218Ⅴ-band CCD images were obtained.We detected a total of 15 stars with variability in visual brightness,including five Be stars,three eclipsing binaries,and seven of unknown types.Two new variable stars were discovered in this work.We also compared the variable star content of NGC 884 with its companion NGC 869.
基金supported by Yunnan Academician Workstation of Wang Jingxiu(202005AF150025)China Manned Space Project(NO.CMSCSST-2021-A08)+1 种基金Guanghe project(ghfund202302019167)the Natural Science Foundation of Yunnan Province(No.202201BC070003)。
文摘Recent studies indicate that some Galactic open clusters(OCs)exhibit extended main-sequence turnoff(eMSTO)in their color–magnitude diagrams(CMDs).However,the number of Galactic OCs with eMSTO structures detected so far is limited,and the reasons for their formation are still unclear.This work identifies 26 Galactic OCs with undiscovered eMSTOs and investigates the causes of these features.Stellar population types and fundamental parameters of cluster samples are acquired using CMD fitting methods.Among them,the results of 11 OCs are reliable as the observed CMDs are well-reproduced.We propose the crucial role of stellar binarity and confirm the importance of stellar rotation in reproducing eMSTO morphologies.The results also show that the impact of age spread is important,as it can adequately explain the structure of young OCs and fit the observed CMDs of intermediate-age OCs better.
基金supported in part by the National Natural Science Foundation of China Nos. 12163006 and 12233006the Basic Research Program of Yunnan Province No. 202201AT070137+1 种基金the joint foundation of Department of Science and Technology of Yunnan Province and Yunnan University No. 202201BF070001-020support by the Xingdian Talent Support Plan-Youth Project。
文摘Recently, a new radio millisecond pulsar(MSP) J1740-5340B, hosted in the globular cluster(GC) NGC 6397,was reported with a 5.78 ms spin period in an eclipsing binary system with a 1.97 days orbital period. Based on a modified radio ephemeris updated by tool tempo2, we analyze the ~15 yr γ-ray data obtained from the Large Area Telescope on board the Fermi Gamma-ray Space Telescope and detect PSR J1740-5340B's γ-ray pulsation at a confidence level of ~4σ with a weighted H-test value of ~26. By performing a phase-resolved analysis, the γ-ray luminosity in on-pulse interval of PSR J1740-5340B is L_(γ)~ 3.8 × 10^(33) erg s^(-1) using NGC 6397's distance of 2.48 kpc. And γ-rays from the on-pulse part of PSR J1740-5340B contribute ~90% of the total observed γ-ray emissions from NGC 6397. No significant γ-ray pulsation of another MSP J1740-5340A in the GC is detected.Considering that the previous four cases of MSPs in GCs, more data in γ-ray, X-ray, and radio are encouraged to finally confirm the γ-ray emissions from MSP J1740-5340B, especially starving for a precise ephemeris.
文摘This paper develops the Dark Matter by Quantum Gravitation theory, DMbQG theory hereafter, in clusters of galaxies in the cosmologic model ΛCDM of the Universe. Originally this theory was developed by the author for galaxies, especially using MW and M31 rotation curves. An important result got by the DMbQG theory is that the total mass associated to a galactic halo depend on the square root of radius, being its dominion unbounded. Apparently, this result would be absurd because of divergence of the total mass. As the DE is negligible at galactic scale, it is needed to extend the theory to clusters in order to study the capacity of DE to counterbalance to DM. Thanks this property, the DMbQG theory finds unexpected theoretical results. In this work, it is defined, the total mass as baryonic matter plus DM and the gravitating mass as the addition of the total mass plus the negative mass associated to dark energy. In clusters it is defined the zero gravity radius (RZG hereafter) as the radius needed by the dark energy to counterbalance the total mass. It has been found that the ratio RZG/RVIRIAL ≈ 7.3 and its Total mass associated at RZG is ≈2.7 MVIRIAL. In addition, it has been calculated that the sphere with the extended halo radius RE = 1.85 RZG has a ratio DM density versus DE density equal to 3/7 and its total mass associated at RE is ≈3.6 MVIRIAL. This works postulates that the factor 3.6 may equilibrate perfectly the strong imbalance between the Local mater density parameter (0.08) versus the current Global matter density one (0.3). Currently, this fact is a big conundrum in cosmology, see chapter 7. Also it has been found that the zero velocity radius, RZV hereafter, i.e. the cluster border because of the Hubble flow, is ≈0.6 RZG and its gravitating mass is ≈ 1.5 MVIR. By derivation of gravitating mass function, it is calculated that at 0.49 RZG, this function reaches its maximum whose value is ≈1.57 MVIR. Throughout the paper, some of these results have been validated with recent data published for the Virgo cluster. As Virgo is the nearest big cluster, it is the perfect benchmark to validate any new theory about DM and DE. These new theoretical findings offer to scientific community a wide number of tests to validate or reject the theory. The validation of DMbQG theory would mean to know the nature of DM that at the present, it is an important challenge for the astrophysics science.
文摘We develop a theoretical formulation for the large-scale dynamics of galaxy clusters involving two spherical 'isothermal fluids' coupled by their mutual gravity and derive asymptotic similarity solutions analytically. One of the fluids roughly approximates the massive dark matter halo, while the other describes the hot gas, the relatively small mass contribution from the galaxies being subsumed in the gas. By properly choosing the self-similar variables, it is possible to consistently transform the set of time-dependent two-fluid equations of spherical symmetry with self-gravity into a set of coupled nonlinear ordinary differential equations (ODEs). We focus on the analytical analysis and discuss applications of the solutions to galaxy clusters.
文摘Clusters of galaxies are the most massive objects in the Universe and precise knowledge of their mass structure is important to understand the history of structure formation and constrain still unknown types of dark contents of the Universe. X-ray spectroscopy of galaxy clusters provides rich information about the physical state of hot intracluster gas and the underlying potential structure. In this paper, starting from the basic description of clusters under equilibrium conditions, we review properties of clusters revealed primarily through X-ray observations considering their thermal and dynamical evolutions. The future prospects of cluster studies using upcoming X-ray missions are also mentioned.
文摘We present an analysis of the winding sense(S and Z-shapes) of 1 621 field galaxies that have radial velocity between 3 000 km s-1 and 5 000 km s-1.The preferred alignments of S-and Z-shaped galaxies are studied using chi-square,autocorrelation and Fourier series tests.We classify all the galaxies into 32 subsamples and notice a good agreement between the position angle(PA) distribution of the S-and Zshaped galaxies.The homogeneous distribution of the S-and Z-shaped galaxies is more noticeable for the late-type spirals(Sc,Scd,Sd and Sm) than for the early-types(Sa,Sab,Sb and Sbc) .A significant dominance of S-mode galaxies is apparent in the barred spirals.A random alignment is evident in the PA-distribution of Z-and S-mode spirals.In addition,a homogeneous distribution of the S-and Z-shaped galaxies is found to be invariant under global expansion.The PA-distribution of the total S-mode galaxies is found to be random,whereas a preferred alignment is clear for all the Zmode galaxies.It is found that the galactic planes of Z-mode galaxies tend to lie in the equatorial plane.
基金the support from the National SKA Program of China No.2020SKA0110102the fund for key programs of Shanghai Astronomical Observatory(Grants E195121009 and E297091002)+1 种基金Shanghai Committee of Science and Technology Grant No.19ZR1466700supported in part by the Natural Science Foundation of China(Grants 12133008,12192220,and 12192223)。
文摘We create mock X-ray observations of hot gas in galaxy clusters with a new extension of the L-Galaxies semianalytic model of galaxy formation,which includes the radial distribution of hot gas in each halo.Based on the model outputs,we first build some mock light cones,then generate mock spectra with the SOXS package and derive the mock images in the light cones.Using the mock data,we simulate mock X-ray spectra for the ROSAT all-sky survey,and compare the mock spectra with the observational results.Then,we consider the design parameters of the HUBS mission and simulate the observation of the halo hot gas for HUBS as an important application of our mock work.We find:(1)our mock data match the observations by current X-ray telescopes.(2)The survey of hot baryons in resolved clusters by HUBS is effective below redshift 0.5,and the observations of the emission lines in point-like sources at z>0.5 by HUBS help us understand the hot baryons in the early universe.(3)By taking advantage of the large simulation box and flexibility in semi-analytic models,our mock X-ray observations provide the opportunity to select targets and observation strategies for forthcoming X-ray facilities.
基金supported by the National SKA Program of China No.2020SKA0110300Joint Research Fund in Astronomy(U1831204)under cooperative agreement between the National Natural Science Foundation of China(NSFC)+5 种基金the Chinese Academy of Sciences(CAS)the National Key Research and Development Program of China(2018YFA0404603)the NSFC(Nos.11863002 and 11961141001)supported by the Yunnan Academician Workstation of Wang Jingxiu(No.202005AF150025)China Manned Space Project with NO.CMS-CSST-2021-A08Sino-German Cooperation Project(No.GZ 1284)。
文摘As groups of coeval stars born from the same molecular cloud,an open cluster(OC)is an ideal laboratory for studying the structure and dynamical evolution of the Milky Way.The release of high-precision Gaia Early Data Release 3(Gaia EDR3)and modern machine-learning methods offer unprecedented opportunities to identify OCs.In this study,we extended conventional HDBSCAN(e-HDBSCAN)for searching for new OCs in Gaia EDR3.A pipeline was developed based on the parallel computing technique to blindly search for OCs from Gaia EDR3within Galactic latitudes∣b∣<25°.As a result,we obtained 3787 star clusters,of which 83 new OCs were reported after cross-match and visual inspection.At the same time,the main star cluster parameters are estimated by color-magnitude diagram fitting.The study significantly increases the sample size and physical parameters of OCs in the catalog of OCs.It shows the incompleteness of the census of OCs across our Galaxy.
基金support by the National Key R&D Program(No.2017YFA0402603)the Inter-government cooperation Flagship program(Grant No.2018YFE0120800)+2 种基金the National Natural Science Foundation of China(NSFC,Grant Nos.11773034 and 11633004)the Chinese Academy of Sciences(CAS)Strategic Priority Research Program XDA15020200the CAS Interdisciplinary Innovation Team(JCTD-2019-05)。
文摘We combine the kinematics of 159 globular clusters(GCs) provided by the Gaia Early Data Release 3(EDR3) with other observational data to classify the GCs,and to estimate the mass of the Milky Way(MW).We use the agemetallicity relation,integrals of motion,action space and the GC orbits to identify the GCs as either formed in situ(Bulge and Disk) or ex situ(via accretion).We find that 45.3% have formed in situ,while 38.4% may be related to known merger events:Gaia-Sausage-Enceladus,the Sagittarius dwarf galaxy,the Helmi streams,the Sequoia galaxy and the Kraken galaxy.We also further identify three new sub-structures associated with the Gaia-Sausage-Enceladus.The remaining 16.3% of GCs are unrelated to the known mergers and thought to be from small accretion events.We select 46 GCs which have radii 8.0 <r<37.3 kpc and obtain the anisotropy parameter β=0.315_(-0.049)^(+0.055),which is lower than the recent result using the sample of GCs in Gaia Data Release 2,but still in agreement with it by considering the error bar.By using the same sample,we obtain the MW mass inside the outermost GC as M(<37.3 kpc)=0.423_(-0.02)^(+0.02)×10^(12)M_(⊙),and the corresponding M_(200)=1.11_(-0.18)^(+0.25)×10^(12)M_(⊙).The estimated mass is consistent with the results in many recent studies.We also find that the estimated β and mass depend on the selected sample of GCs.However,it is difficult to determine whether a GC fully traces the potential of the MW.
基金supported by the National SKA Program of China No.2020SKA0120100the National Natural Science Foundation of China(NSFC,Grant Nos.11963002,11703047,11773041,U2031119,12173052,12003047 and 12173053)+7 种基金the fostering project of Guizhou University with No.201911Cultivation Project for FAST Scientific Payoff and Research Achievement of CAMS-CASsupported by the Specialized Research Fund for State Key Laboratoriessupported by the CAS“Light of West China”Programthe Youth Innovation Promotion Association of CAS(id 2023064)supported by the Youth Innovation Promotion Association of CAS(id.2018075 and Y2022027)supported by Guizhou Provincial Basic Research Program(Natural Science)(ZK[2023]039)Key Technology R&D Program([2023]352)。
文摘Up to 2022 November,267 pulsars had been discovered in 36 globular clusters(GCs).In this paper,we present our studies on the distribution of GC pulsar parameters and the detection efficiency.The power law relation between average dispersion measure(■)and dispersion measure difference(ΔDM)of known pulsars in GCs is lgΔDM∝1.52lg■.The sensitivity could be the key to finding more pulsars.As a result,several years after the construction of a large radio telescope facility,the number of known GC pulsars will likely be increased accordingly.We suggest that currently GCs in the southern hemisphere could have higher possibilities for finding new pulsars.
基金supported by the National Natural Science Foundation of China(NSFC,Grant Nos.11863002 and 11673032)Yunnan Academician Workstation of Wang Jingxiu(202005AF150025)+7 种基金China Manned Space Project with No.CMS-CSST-2021-A08Sino-German Cooperation Project(No.GZ 1284)supported by the Volkswagen Foundation under the special stipend No.9B870(2022)the support within the grant No.AP14869395 of the Science Committee of the Ministry of Science,Higher Education of Kazakhstan(“Triune model of Galactic center dynamical evolution on cosmological timescale”)Ministry of Education and Science of Ukraine under the collaborative grant M/32-23.05.2022the National Academy of Sciences of Ukraine under the Main Astronomical Observatory GPU computing cluster project No.13.2021.MMsupported by the Deutsche Forschungsgemeinschaft(DFG,German Research Foundation)-ProjectID 138713538—SFB 881(“The Milky Way System”)by the Volkswagen Foundation under the Trilateral Partnerships grant Nos.90411 and 97778。
文摘The binary population in field stars and star clusters contributes to the formation of gravitational wave(GW)sources.However,the fraction of compact-object binaries(CBs),which is an important feature parameter of binary populations,is still difficult to measure and very uncertain.This paper predicts the fractions of important CBs and semi-compact object binaries(SCBs) making use of an advanced stellar population synthesis technique.A comparison with the result of N-body simulation is also presented.It is found that most CBs are formed within about 500 Myr after the starburst.The fractions of CBs and SCBs are demonstrated to correlate with stellar metallicity.The higher the metallicity becomes,the smaller the fraction of black hole binaries(BHBs),neutron star binaries(NSBs) and SCBs.This suggests that the GW sources of BHBs and NSBs are more likely to form in metal-poor environments.However,the fraction of black hole-neutron star binaries is shown to be larger for metalrich populations on average.
基金supported in part by China Manned Space Project with NO.CMS-CSST-2021-A08the National Natural Science Foundation of China(NSFC,Grants Nos.12233009,12233013,12073090 and 12003001)。
文摘The China Space Station Telescope(CSST)is a 2 m space-based optical-UV telescope.Its primary goal is to carry out a high-resolution photometric imaging survey of a 17,500 square degree sky area using the on board Survey Camera.With its wide field of view(1.1 square degrees)and a mosaic imager containing 640 million pixels,studying the different populations of stars within star clusters is highly feasible.The aim of this study is to assess the CSST's ability to distinguish between stellar populations with varying helium abundance levels,with the help of Modules for Experiments in Stellar Astrophysics.The results of the CSST's photometry for these different populations are presented by transferring the models into the CSST Survey Camera photometric system.The findings confirm that helium-enriched stellar populations will have unique patterns in the color-magnitude diagrams under the CSST photometric system,compared to normal stellar populations.The CSST,with its filters and wide field of view of the Survey Camera,provides a new avenue for the study of multiple populations in star clusters.
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 National Key R&D Program of China(grant No.2023YFE0117200)the National Natural Science Foundation of China(NSFC,grant Nos.12133003,12103011)+2 种基金R-Z.Y.is supported by the NSFC under grants 11421303,12041305Science and Technology Program of Guangxi(grant Nos.AD 21220075 and 2024GXNSFBA010375)the national youth thousand talents program in China。
文摘We revisit the γ-ray emission above 300 Me V towards the massive star-forming region of Orion B by adopting14 yr observations with the Fermi Large Area Telescope and utilizing the updated software tools.The extended γ-ray emission region around Orion B is resolved into two components(region Ⅰ and region Ⅱ).The γ-ray spectrum of region I agrees with the predicted γ-ray spectrum assuming the cosmic ray(CR)density is the same as that of Alpha Magnetic Spectrometer(AMS-02)measured locally.Theγ-ray emissivity of region II appears to be deficit at low energy band(E<3 GeV).Through modeling we find that CR densities exhibit a significant deficit below 20 Ge V,which may be caused by a slow diffusion inside the dense region.This is probably caused by an increased magnetic field whose strength increases with the gas density.