The problem of the chemical composition gradient in the Galactic disk is studied based on a sample of metallicity estimates of open star clusters,using Gaia DR2-improved distance estimates.A clearly non-monotonic vari...The problem of the chemical composition gradient in the Galactic disk is studied based on a sample of metallicity estimates of open star clusters,using Gaia DR2-improved distance estimates.A clearly non-monotonic variation was observed in the average metallicity of clusters with increasing Galactocentric distance.One can clearly see the metallicity jump of 0.22 in[Fe/H]at a Galactocentric distance of about9.5 kpc,which appears to be linked to the outer boundary of the thinnest and youngest component of the Galactic disk.The absence of a significant metallicity gradient in the internal(R<9 kpc)and external(R>10 kpc)regions of the disk demonstrates the absence of noticeable metal enrichment at times of the order of the ages corresponding to those of the disk regions under consideration.Observational data show that the disk experiences noticeable metal enrichment only during the starburst epochs.No significant dependence was identified between the average metallicity and the age of the clusters.展开更多
Using the three-component spectral model describing the FIRAS average continuum spectra, the exact analytical expressions for thermodynamic and radiative functions of Galactic far-infrared radiation are obtained. The ...Using the three-component spectral model describing the FIRAS average continuum spectra, the exact analytical expressions for thermodynamic and radiative functions of Galactic far-infrared radiation are obtained. The COBE FIRAS instrument data in the 0.15-2.88 THz frequency interval at the mean temperatures of T1= 17.72 K, T2= 14 K and T3= 6.73 K are used for calculating the radiative and thermodynamic functions, such as the total radiation power per unit area, total energy density, total emissivity, number density of photons, Helmholtz free energy density, entropy density, heat capacity at constant volume and pressure for the warm,intermediate-temperature and very cold components of the Galactic continuum spectra. The generalized Stefan-Boltzmann law for warm, intermediate-temperature and very cold components is constructed. The temperature dependence of each component is determined by the formula IS-B（T） = σ′ T6. This result is important when we construct the cosmological models of radiative transfer that can be applied inside the Galaxy. Within the framework of the three-component spectral model, the total number of photons in our Galaxy and the total radiation power（total luminosity） emitted from a surface of the Galaxy are calculated. Their values are N6Gtotal= 1.3780 × 108 and I3Gtotal（T） = 1.0482 × 106 W. Other radiative and thermodynamic properties of the Galactic far-infrared radiation（photon gas） of the Galaxy are calculated. The expressions for astrophysical parameters, such as the entropy density/Boltzmann constant and number density of the Galactic far-infrared photons are obtained. We assume that the obtained analytical expressions for thermodynamic and radiative functions may be useful for describing the continuum spectra of the far-infrared radiation for other galaxies.展开更多
The currently used Galactic coordinate system（GalC S） is based on the FK5 system at J2000.0, which was transformed from the FK4 system at B1950.0.The limitations and misunderstandings related to this transformed Gal...The currently used Galactic coordinate system（GalC S） is based on the FK5 system at J2000.0, which was transformed from the FK4 system at B1950.0.The limitations and misunderstandings related to this transformed GalC S can be avoided by defining a new GalC S that is directly connected to the International Celestial Reference System（ICRS）. With more data at various wavelengths released by large survey programs, a more appropriate GalC S consistent with features associated with the Milky Way can be established. We try to find the best orientation of the GalC S using data from two all-sky surveys, AKARI and WISE, at six wavelengths between 3.4 μm and 90 μm, and synthesize results obtained at various wavelengths to define an improved GalC S in the framework of the ICRS. The revised GalC S parameters for defining the new GalC S in the ICRS are summarized as：αp= 192.777°, δp= 26.9298°, for the equatorial coordinates of the north Galactic pole and θ = 122.95017° for the position angle of the Galactic center. As one of the Galactic substructures, the Galactic warp exhibits different forms in different GalC Ss that are constructed with various data and methods, which shows the importance of re-defining the GalC S by the relative commission of the International Astronomical Union that can lead to a better understanding of Galactic structure and kinematics.展开更多
We study the counts of resolved SZE (Sunyaev-Zel'dovich effect) clusters expected from an interferometric survey in different cosmological models under different conditions. The self-similar universal gas model an...We study the counts of resolved SZE (Sunyaev-Zel'dovich effect) clusters expected from an interferometric survey in different cosmological models under different conditions. The self-similar universal gas model and Press-Schechter mass function are used. We take the observing frequency to be 90 GHz, and consider two dish diameters, 1.2 m and 2.5 m. We calculate the number density of the galaxy clusters dN/(dΩdz) at a high flux limit S<SUB>v</SUB><SUP>lim</SUP>=100 mJy and at a relative low S<SUB>v</SUB><SUP>lim</SUP> =10 mJy. The total numbers of SZE clusters N in two low-Ω<SUB>0</SUB> models are compared. The results show that the influence of the resolved effect depends not only on D, but also on S<SUB>v</SUB><SUP>lim</SUP>: at a given D, the effect is more significant for a high than for a low S<SUB>v</SUB><SUP>lim</SUP>. Also, the resolved effect for a flat universe is more impressive than that for an open universe. For D = 1.2 m and S<SUB>v</SUB><SUP>lim</SUP> =10 mJy, the resolved effect is very weak. Considering the designed interferometers which will be used to survey SZE clusters, we find that the resolved effect is insignificant when estimating the expected yield of the SZE cluster surveys.展开更多
We investigate the mass-temperature relation of clusters for both the spherical NFW halo model and a concentric triaxial halo model. We study the temperature and density distributions of both an isothermal and a polyt...We investigate the mass-temperature relation of clusters for both the spherical NFW halo model and a concentric triaxial halo model. We study the temperature and density distributions of both an isothermal and a polytropic intra-cluster gas in hydrostatic equilibrium. We find that both the uncertainties in the concentration parameter and in the eccentricities (in case of the triaxial halo) lead to a greater scatter in the emission-weighted temperature at a given halo mass for less massive clusters. This may be helpful when determining the intrinsic statistical error of the σ<SUB>8</SUB> normalization of the linear power spectrum from cluster abundance.展开更多
基金supported in part by the Ministry of Education and Science(the basic part of the State assignment RK No.AAAA-A17-117030310283-7)Act No.211 of the Government of the Russian Federation(No.02.A03.21.0006)。
文摘The problem of the chemical composition gradient in the Galactic disk is studied based on a sample of metallicity estimates of open star clusters,using Gaia DR2-improved distance estimates.A clearly non-monotonic variation was observed in the average metallicity of clusters with increasing Galactocentric distance.One can clearly see the metallicity jump of 0.22 in[Fe/H]at a Galactocentric distance of about9.5 kpc,which appears to be linked to the outer boundary of the thinnest and youngest component of the Galactic disk.The absence of a significant metallicity gradient in the internal(R<9 kpc)and external(R>10 kpc)regions of the disk demonstrates the absence of noticeable metal enrichment at times of the order of the ages corresponding to those of the disk regions under consideration.Observational data show that the disk experiences noticeable metal enrichment only during the starburst epochs.No significant dependence was identified between the average metallicity and the age of the clusters.
文摘Using the three-component spectral model describing the FIRAS average continuum spectra, the exact analytical expressions for thermodynamic and radiative functions of Galactic far-infrared radiation are obtained. The COBE FIRAS instrument data in the 0.15-2.88 THz frequency interval at the mean temperatures of T1= 17.72 K, T2= 14 K and T3= 6.73 K are used for calculating the radiative and thermodynamic functions, such as the total radiation power per unit area, total energy density, total emissivity, number density of photons, Helmholtz free energy density, entropy density, heat capacity at constant volume and pressure for the warm,intermediate-temperature and very cold components of the Galactic continuum spectra. The generalized Stefan-Boltzmann law for warm, intermediate-temperature and very cold components is constructed. The temperature dependence of each component is determined by the formula IS-B（T） = σ′ T6. This result is important when we construct the cosmological models of radiative transfer that can be applied inside the Galaxy. Within the framework of the three-component spectral model, the total number of photons in our Galaxy and the total radiation power（total luminosity） emitted from a surface of the Galaxy are calculated. Their values are N6Gtotal= 1.3780 × 108 and I3Gtotal（T） = 1.0482 × 106 W. Other radiative and thermodynamic properties of the Galactic far-infrared radiation（photon gas） of the Galaxy are calculated. The expressions for astrophysical parameters, such as the entropy density/Boltzmann constant and number density of the Galactic far-infrared photons are obtained. We assume that the obtained analytical expressions for thermodynamic and radiative functions may be useful for describing the continuum spectra of the far-infrared radiation for other galaxies.
基金Supported by the National Natural Science Foundation of China
文摘The currently used Galactic coordinate system（GalC S） is based on the FK5 system at J2000.0, which was transformed from the FK4 system at B1950.0.The limitations and misunderstandings related to this transformed GalC S can be avoided by defining a new GalC S that is directly connected to the International Celestial Reference System（ICRS）. With more data at various wavelengths released by large survey programs, a more appropriate GalC S consistent with features associated with the Milky Way can be established. We try to find the best orientation of the GalC S using data from two all-sky surveys, AKARI and WISE, at six wavelengths between 3.4 μm and 90 μm, and synthesize results obtained at various wavelengths to define an improved GalC S in the framework of the ICRS. The revised GalC S parameters for defining the new GalC S in the ICRS are summarized as：αp= 192.777°, δp= 26.9298°, for the equatorial coordinates of the north Galactic pole and θ = 122.95017° for the position angle of the Galactic center. As one of the Galactic substructures, the Galactic warp exhibits different forms in different GalC Ss that are constructed with various data and methods, which shows the importance of re-defining the GalC S by the relative commission of the International Astronomical Union that can lead to a better understanding of Galactic structure and kinematics.
文摘We study the counts of resolved SZE (Sunyaev-Zel'dovich effect) clusters expected from an interferometric survey in different cosmological models under different conditions. The self-similar universal gas model and Press-Schechter mass function are used. We take the observing frequency to be 90 GHz, and consider two dish diameters, 1.2 m and 2.5 m. We calculate the number density of the galaxy clusters dN/(dΩdz) at a high flux limit S<SUB>v</SUB><SUP>lim</SUP>=100 mJy and at a relative low S<SUB>v</SUB><SUP>lim</SUP> =10 mJy. The total numbers of SZE clusters N in two low-Ω<SUB>0</SUB> models are compared. The results show that the influence of the resolved effect depends not only on D, but also on S<SUB>v</SUB><SUP>lim</SUP>: at a given D, the effect is more significant for a high than for a low S<SUB>v</SUB><SUP>lim</SUP>. Also, the resolved effect for a flat universe is more impressive than that for an open universe. For D = 1.2 m and S<SUB>v</SUB><SUP>lim</SUP> =10 mJy, the resolved effect is very weak. Considering the designed interferometers which will be used to survey SZE clusters, we find that the resolved effect is insignificant when estimating the expected yield of the SZE cluster surveys.
基金Supported by the National Natural Science Foundation of China
文摘We investigate the mass-temperature relation of clusters for both the spherical NFW halo model and a concentric triaxial halo model. We study the temperature and density distributions of both an isothermal and a polytropic intra-cluster gas in hydrostatic equilibrium. We find that both the uncertainties in the concentration parameter and in the eccentricities (in case of the triaxial halo) lead to a greater scatter in the emission-weighted temperature at a given halo mass for less massive clusters. This may be helpful when determining the intrinsic statistical error of the σ<SUB>8</SUB> normalization of the linear power spectrum from cluster abundance.
