We used multi-component profiles to model the HE and [O Ⅲ]λλ4959,5007 lines of SDSS J143030.22-001115.1, a narrow-line Seyfert 1 galaxy （NLS1） in a sample of 150 NLS1 candidates selected from the Sloan Digital Sk...We used multi-component profiles to model the HE and [O Ⅲ]λλ4959,5007 lines of SDSS J143030.22-001115.1, a narrow-line Seyfert 1 galaxy （NLS1） in a sample of 150 NLS1 candidates selected from the Sloan Digital Sky Survey （SDSS）, Early Data Release （EDR）. After subtracting the HE contribution from narrow line regions （NLRs）, we found that its full width half maximum （FWHM） of broad H/3 line is nearly 2900km s^-1, significantly larger than the customarily adopted criterion of 2000 km s^-1. With its weak Fe II multiples, we believe that SDSS J143030.22-001115.1 should not be classified as a genuine NLS1. When we calculate the virial black hole masses of NLSls, we should use the Hβ linewidth after subtracting the NLR component.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
Recently, Sun et al. published new Galactic 3D-models of magnetic fields in the disk and halo of the Milky Way and the distribution of cosmic-ray electron density by taking into account the thermal electron density mo...Recently, Sun et al. published new Galactic 3D-models of magnetic fields in the disk and halo of the Milky Way and the distribution of cosmic-ray electron density by taking into account the thermal electron density model NE2001 by Cordes ＆ Lazio. The models successfully reproduce observed continuum and polarization all-sky maps and the distribution of rotation measures of extragalactic sources across the sky. However, the model parameters obtained for the Galactic halo, although reproducing the observations, seem physically unreasonable： the magnetic field needs to be significantly stronger in the Galactic halo than in the plane and the cosmic-ray distribution must be truncated at about 1 kpc to avoid excessive synchrotron emission from the halo. The reason for these unrealistic parameters was the low scale-height of the warm thermal gas of about 1 kpc adopted in the NE2001 model. However, this scale- height seemed reasonable and was well studied by numerous investigations. Recently, the scale-height of the warm gas in the Galaxy was revised by Gaensler et al. to about 1.8 kpc, by showing that the 1 kpc scale-height results from a systematic bias in the analysis of pulsar data. This implies a higher thermal electron density in the Galactic halo, which in turn reduces the halo magnetic field strength to account for the observed rotation measures of extragalactic sources. We slightly modified the NE2001 model according to the new scale-height and revised the Sun et al. model parameters accordingly： the strength of the regular halo magnetic field is now 2 μG or lower, and the physically unrealistic cutoff in z for the cosmic-ray electron density is removed. The simulations based on the revised 3D-models reproduce all-sky observations as before.展开更多
We aim to retrieve ghost streams under the assumption that all the globular clusters in our Galaxy were formed in very early merge events. Our results are based on two speculations： that the specific energy and angul...We aim to retrieve ghost streams under the assumption that all the globular clusters in our Galaxy were formed in very early merge events. Our results are based on two speculations： that the specific energy and angular momentum of the globular clusters after merge are not changed in the course of evolution and that the globular clusters with a common origin would stay in the same orbit plane as the parent galaxy. After taking into account the apogalacticum distance of the orbits, we suggest with some Confidence five possible streams. The number of streams is consistent with the previous results. Three of the four well established members of the Sagittadus stream were found to be in one of our streams. Several other globular clusters in our result were also thought to come from accretion by previous researchers. The orbital parameters of the streams are derived, which provide a way to test whether these streams are true with the help of more accurate measurement of proper motions of the globular clusters.展开更多
We report on our research on the UV, optical line parameters and the infrared through UV to soft X-ray continuum parameters for a composite sample of narrow line and normal Seyfert 1 galaxies. The strong correlations ...We report on our research on the UV, optical line parameters and the infrared through UV to soft X-ray continuum parameters for a composite sample of narrow line and normal Seyfert 1 galaxies. The strong correlations among the line width of HB, optical line strength of Fell and the soft X-ray slope are confirmed. We found no correlations between the UV line parameters, the equivalent widths of Lya and CIV and their ratio on one hand and the optical line parameters on the other. The UV and X-ray luminosities strongly correlate with the line widths of HB and the Fe II/HB ratio. No significant correlation is found between the infrared-soft X-my continuum slope aix and the line width of HB.展开更多
For investigating the statistical properties of X-ray selected Active Galactic Nuclei (AGNs), we have carried out a program of optical identification of a selection of X-ray sources from ROSAT All Sky Survey Bright So...For investigating the statistical properties of X-ray selected Active Galactic Nuclei (AGNs), we have carried out a program of optical identification of a selection of X-ray sources from ROSAT All Sky Survey Bright Source Catalogue (RASS-BSC) using the 2.16 m telescope of Beijing Astronomical Observatory (BAO). In the preliminary observations, 23 new AGNs were discovered, of which 9 are quasars, and 14 are Seyfert galaxies.展开更多
The Galactic halo is supposed to form from merging with nearby dwarf galaxies.In order to probe different components of the Galactic halo,we have applied the Gaussian Mixture Models method to a selected sample of meta...The Galactic halo is supposed to form from merging with nearby dwarf galaxies.In order to probe different components of the Galactic halo,we have applied the Gaussian Mixture Models method to a selected sample of metal poor stars with[Fe/H]<−0.7 dex in the APOGEE DR16 catalogue based on four-parameters,metallicity,[Mg/Fe]ratio and spatial velocity(VR,V).Nine groups are identified with four from the halo(group 1,3,4 and 5),one from the thick disk(group 6),one from the thin disk(group 8)and one from dwarf galaxies(group 7)by analyzing their distributions in the([M/H],[Mg/Fe]),(VR,V),(Zmax,eccentricity),(Energy,Lz)and([Mg/Mn],[Al/Fe])coordinates.The rest of the two groups are respectively caused by observational effect(group 9)and the cross section component(group 2)between the thin disk and the thick disk.It is found that in the extremely outer accreted halo(group 1),stars born in the Milky Way cannot be distinguished from those accreted from other galaxies either chemically or kinematically.In the intermediate metallicity of−1.6<[Fe/H]<−0.7 dex,the accreted halo is mainly composed of the Gaia-Enceladus-Sausage substructure(group 5),which can be easily distinguished from group 4(the in-situ halo group)in both chemical and kinematic space.Some stars of group 4 may come from the disk and some disk stars can be scattered to high orbits by resonant effects as shown in the Zmax versus Energy coordinate.We also displayed the spatial distribution of main components of the halo and the ratio of accreted components do not show clear relation to the Galactic radius.展开更多
The iron abundance gradient in the Galactic disk provides fundamental constraints on the chemical evolution of this important component of the Galaxy.However,there are still some arguments about the shape of the iron ...The iron abundance gradient in the Galactic disk provides fundamental constraints on the chemical evolution of this important component of the Galaxy.However,there are still some arguments about the shape of the iron abundance gradient across the Galactic stellar disk.To provide quantitative constraints on these trends,we constructed an unbiased stellar sample from the common objects of two large observations.The sample consists of 4004 disk stars in the solar neighborhood with the range of metallicity [Fe/H] from ^-1.0 to ~0.5,including 3855 thin disk stars and 146 thick disk stars.The range of their mean Galactocentric distances R m is from ~4 to ~11 kpc,and the range of their maximum vertical distance from the Galactic Plane Z max is from 0 to ~3.5 kpc.The relations of the stellar metallicity [Fe/H] with the orbital eccentricity e,and [Fe/H] with R m,as well as [Fe/H] with Z max are investigated in detail.The results showed that:(1) The orbital eccentricity of disk stars decreases with increasing metallicity,while this trend becomes flat for stars with [Fe/H]】-0.2.(2) For thin disk,there is a clear radial iron gradient of-0.051±0.005 dex/kpc.However,this metallicity gradient is discontinuous once we split the sample into the inner(Rm【8kpc) and outer disk(Rm≥8 kpc):a slope of about 0 dex/kpc is present in the inner disk and a slope of-0.12 dex/kpc is in the outer disk.For the thick disk,there is no trend of [Fe/H] with R m.(3) The vertical gradient of iron abundance is-0.146 dex/kpc and-0.251 dex/kpc for the thick and thin disks,respectively.Moreover,the vertical abundance gradient shows a steeper trend with the evolution of the Galaxy.Our results confirm the collapse mechanism associated with the formation and evolution of the Galactic disk.展开更多
基金Supported by the National Natural Science Foundation of China.
文摘We used multi-component profiles to model the HE and [O Ⅲ]λλ4959,5007 lines of SDSS J143030.22-001115.1, a narrow-line Seyfert 1 galaxy （NLS1） in a sample of 150 NLS1 candidates selected from the Sloan Digital Sky Survey （SDSS）, Early Data Release （EDR）. After subtracting the HE contribution from narrow line regions （NLRs）, we found that its full width half maximum （FWHM） of broad H/3 line is nearly 2900km s^-1, significantly larger than the customarily adopted criterion of 2000 km s^-1. With its weak Fe II multiples, we believe that SDSS J143030.22-001115.1 should not be classified as a genuine NLS1. When we calculate the virial black hole masses of NLSls, we should use the Hβ linewidth after subtracting the NLR component.
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.
文摘Recently, Sun et al. published new Galactic 3D-models of magnetic fields in the disk and halo of the Milky Way and the distribution of cosmic-ray electron density by taking into account the thermal electron density model NE2001 by Cordes ＆ Lazio. The models successfully reproduce observed continuum and polarization all-sky maps and the distribution of rotation measures of extragalactic sources across the sky. However, the model parameters obtained for the Galactic halo, although reproducing the observations, seem physically unreasonable： the magnetic field needs to be significantly stronger in the Galactic halo than in the plane and the cosmic-ray distribution must be truncated at about 1 kpc to avoid excessive synchrotron emission from the halo. The reason for these unrealistic parameters was the low scale-height of the warm thermal gas of about 1 kpc adopted in the NE2001 model. However, this scale- height seemed reasonable and was well studied by numerous investigations. Recently, the scale-height of the warm gas in the Galaxy was revised by Gaensler et al. to about 1.8 kpc, by showing that the 1 kpc scale-height results from a systematic bias in the analysis of pulsar data. This implies a higher thermal electron density in the Galactic halo, which in turn reduces the halo magnetic field strength to account for the observed rotation measures of extragalactic sources. We slightly modified the NE2001 model according to the new scale-height and revised the Sun et al. model parameters accordingly： the strength of the regular halo magnetic field is now 2 μG or lower, and the physically unrealistic cutoff in z for the cosmic-ray electron density is removed. The simulations based on the revised 3D-models reproduce all-sky observations as before.
基金Supported by the National Natural Science Foundation of China.
文摘We aim to retrieve ghost streams under the assumption that all the globular clusters in our Galaxy were formed in very early merge events. Our results are based on two speculations： that the specific energy and angular momentum of the globular clusters after merge are not changed in the course of evolution and that the globular clusters with a common origin would stay in the same orbit plane as the parent galaxy. After taking into account the apogalacticum distance of the orbits, we suggest with some Confidence five possible streams. The number of streams is consistent with the previous results. Three of the four well established members of the Sagittadus stream were found to be in one of our streams. Several other globular clusters in our result were also thought to come from accretion by previous researchers. The orbital parameters of the streams are derived, which provide a way to test whether these streams are true with the help of more accurate measurement of proper motions of the globular clusters.
基金the National Natural Science Foundationof China and Chinese Panden Project.
文摘We report on our research on the UV, optical line parameters and the infrared through UV to soft X-ray continuum parameters for a composite sample of narrow line and normal Seyfert 1 galaxies. The strong correlations among the line width of HB, optical line strength of Fell and the soft X-ray slope are confirmed. We found no correlations between the UV line parameters, the equivalent widths of Lya and CIV and their ratio on one hand and the optical line parameters on the other. The UV and X-ray luminosities strongly correlate with the line widths of HB and the Fe II/HB ratio. No significant correlation is found between the infrared-soft X-my continuum slope aix and the line width of HB.
文摘For investigating the statistical properties of X-ray selected Active Galactic Nuclei (AGNs), we have carried out a program of optical identification of a selection of X-ray sources from ROSAT All Sky Survey Bright Source Catalogue (RASS-BSC) using the 2.16 m telescope of Beijing Astronomical Observatory (BAO). In the preliminary observations, 23 new AGNs were discovered, of which 9 are quasars, and 14 are Seyfert galaxies.
基金This study is supported by the National Natural Science Foundation of China(Grant Nos.11988101,11625313,11973048,11927804 and 11890694)the National Key R&D Program of China(Grant No.2019YFA0405502)the 2-m Chinese Space Survey Telescope project and the Fundamental Research Funds for the Central Universities(Grants No.292020001734(E0E48956)).
文摘The Galactic halo is supposed to form from merging with nearby dwarf galaxies.In order to probe different components of the Galactic halo,we have applied the Gaussian Mixture Models method to a selected sample of metal poor stars with[Fe/H]<−0.7 dex in the APOGEE DR16 catalogue based on four-parameters,metallicity,[Mg/Fe]ratio and spatial velocity(VR,V).Nine groups are identified with four from the halo(group 1,3,4 and 5),one from the thick disk(group 6),one from the thin disk(group 8)and one from dwarf galaxies(group 7)by analyzing their distributions in the([M/H],[Mg/Fe]),(VR,V),(Zmax,eccentricity),(Energy,Lz)and([Mg/Mn],[Al/Fe])coordinates.The rest of the two groups are respectively caused by observational effect(group 9)and the cross section component(group 2)between the thin disk and the thick disk.It is found that in the extremely outer accreted halo(group 1),stars born in the Milky Way cannot be distinguished from those accreted from other galaxies either chemically or kinematically.In the intermediate metallicity of−1.6<[Fe/H]<−0.7 dex,the accreted halo is mainly composed of the Gaia-Enceladus-Sausage substructure(group 5),which can be easily distinguished from group 4(the in-situ halo group)in both chemical and kinematic space.Some stars of group 4 may come from the disk and some disk stars can be scattered to high orbits by resonant effects as shown in the Zmax versus Energy coordinate.We also displayed the spatial distribution of main components of the halo and the ratio of accreted components do not show clear relation to the Galactic radius.
基金supported by the National Natural Science Foundation of China (Grant Nos. 10778616 and 10673002)
文摘The iron abundance gradient in the Galactic disk provides fundamental constraints on the chemical evolution of this important component of the Galaxy.However,there are still some arguments about the shape of the iron abundance gradient across the Galactic stellar disk.To provide quantitative constraints on these trends,we constructed an unbiased stellar sample from the common objects of two large observations.The sample consists of 4004 disk stars in the solar neighborhood with the range of metallicity [Fe/H] from ^-1.0 to ~0.5,including 3855 thin disk stars and 146 thick disk stars.The range of their mean Galactocentric distances R m is from ~4 to ~11 kpc,and the range of their maximum vertical distance from the Galactic Plane Z max is from 0 to ~3.5 kpc.The relations of the stellar metallicity [Fe/H] with the orbital eccentricity e,and [Fe/H] with R m,as well as [Fe/H] with Z max are investigated in detail.The results showed that:(1) The orbital eccentricity of disk stars decreases with increasing metallicity,while this trend becomes flat for stars with [Fe/H]】-0.2.(2) For thin disk,there is a clear radial iron gradient of-0.051±0.005 dex/kpc.However,this metallicity gradient is discontinuous once we split the sample into the inner(Rm【8kpc) and outer disk(Rm≥8 kpc):a slope of about 0 dex/kpc is present in the inner disk and a slope of-0.12 dex/kpc is in the outer disk.For the thick disk,there is no trend of [Fe/H] with R m.(3) The vertical gradient of iron abundance is-0.146 dex/kpc and-0.251 dex/kpc for the thick and thin disks,respectively.Moreover,the vertical abundance gradient shows a steeper trend with the evolution of the Galaxy.Our results confirm the collapse mechanism associated with the formation and evolution of the Galactic disk.
