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Dynamical Evolution Of Globular Clusters In Hierarchical Cosmology

机译:分层宇宙学中球状星团的动态演化

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We test the hypothesis that metal-poor globular clusters form within disk galaxies at redshifts z > 3. We calculate the orbits of model clusters in the time-variable gravitational potential of a Milky Way-sized galaxy, using the outputs of a cosmological N-body simulation. We find that at present the orbits are isotropic in the inner 50 kpc of the Galaxy and preferentially radial at larger distances. All clusters located outside 10 kpc from the center formed in satellite galaxies, some of which are now tidally disrupted and some of which survive as dwarf galaxies. Mergers of the progenitors lead to a spheroidal spatial distribution of model clusters, although it is more extended than that of Galactic metal-poor clusters and has a somewhat shallower power-law slope of the number density profile, γ ≈ 2.7. The combination of two-body relaxation, tidal shocks, and stellar evolution drives the evolution of the cluster mass function from an initial power law to a peaked distribution, in agreement with observations. However, not all initial conditions and not all evolution scenarios are consistent with the observed mass function of the Galactic globular clusters. We find that our best-fitting models require the average cluster density, M/R_h~3, to be constant initially for clusters of all mass and to remain constant with time. However, these models do not explain the observed decrease of the mean density with galactocentric distance. Both synchronous formation of all clusters at a single epoch (2 = 4) and continuous formation over a span of 1.6 Gyr (between z = 9 and 3) are consistent with the data. For both formation scenarios, we provide online catalogs of the main physical properties of model clusters.
机译:我们测试了以下假设:在红移z> 3时,盘状星系中形成了金属贫乏球状星团。我们使用宇宙学N-的输出,计算了银河系大小星系随时间变化的引力势中模型星团的轨道。人体模拟。我们发现,目前,在银河系内部50 kpc内,各轨道是各向同性的,并且在较大距离处最好是径向的。所有位于距星系中心10 kpc之外的星团,都形成了卫星星系,其中一些现在被潮汐破坏,其中一些作为矮星系生存。祖先的合并导致了模型簇的球状空间分布,尽管它比银河贫金属簇的球形分布更扩展,并且其数密度曲线的幂律斜率略浅,γ≈2.7。与观测结果一致,两体松弛,潮汐冲击和恒星演化的结合驱使簇质量函数从初始幂定律演化为峰值分布。但是,并非所有初始条件和所有演化情况都与银河系球状星团的观测质量函数一致。我们发现,最适合的模型要求平均簇密度M / R_h〜3对于所有质量的簇最初要保持恒定,并随时间保持恒定。但是,这些模型不能解释所观测到的平均密度随galotocentric距离的减少。在一个时期(2 = 4)同步形成所有星团,以及在1.6 Gyr的跨度(z = 9和3之间)连续形成都与数据一致。对于这两种形成方案,我们都提供了模型簇主要物理性质的在线目录。

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