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Determination of the Thickness of Non-Edge-on Disk galaxies

Chinese Journal of Astronomy and Astrophysics 2004年第1期4卷 51-60页

作者： Ying-HeZhao Qiu-HePeng LanWang DepartmentofAstronomy NanjingUniversityNanjing210093 JointAstrophysicsCenterofChineseAcademyofScience-PekingUniversity Beijing100871

We propose a method to determine the thickness of non-edge-on disk galaxies from their observed structure of spiral arms, based on the solution of the truly three-dimensional Poisson's equation for a logarithmic disturbance of density and under the condition where the self-consistency of the density wave theory is no longer valid. From their measured number of arms, pitch angle and location of the innermost point of the spiral arms, we derive and present the thicknesses of 34 spiral galaxies.

关键词： galaxies: non-edge-on galaxies galaxies: spiral thickness: density wavetheory

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TeV cosmic-ray proton and helium spectra in the myriad model Ⅱ

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Research in Astronomy and Astrophysics 2015年第1期15卷 15-27页

作者： Wei Liu Pierre Salati Xuelei Chen National Astronomical Observatories Chinese Academy of Science University of Chinese Academy of Sciences LAPTh Universit'e de Savoie CNRS BP 110 74941 Annecy-le-Vieux France Center of High Energy Physics Peking University

Recent observations show that the spectra of cosmic ray nuclei start to harden above ～ 102 GeV, which contradicts the conventional steady-state cosmic ray model. We had suggested that this anomaly is due to the propagation effect of cosmic rays released from local young cosmic ray sources; the total flux of cosmic rays should be computed with the Myriad Model, where a contribution from sources in the local catalog is added to the background. However, although the hardening could be elegantly explained in this model, the model parameters obtained from the fit are skewed toward a region with fast diffusion and a low supernova rate in the Galaxy, in disagreement with other observations. We further explore this model in order to set up a concordant picture. Two possible improvements related to cosmic ray sources are considered. First, instead of the usual axisymmetric disk model, we examine a spiral model for the source distribution. Second, for nearby and young sources which are necessary to explain the hardening, we allow for an energy-dependent escape. We find that a major improvement comes from incorporating an energy-dependent escape time for local sources, and with both modifications not only are the cosmic ray proton and helium anomalies resolved, but also the parameters attain values in a reasonable range compatible with other analyses.

关键词： catalogs cosmic rays pulsars: general galaxies: spiral

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