The axial zone of avoidance in the globular cluster system and the distance to the galactic center

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• 作者：I. I. Nikiforov ; E. V. Agladze
• 关键词：globular cluster system ; spatial distribution ; structure ; solar Galactocentric distance ; Galaxy (Milky Way)
• 刊名：Astronomy Letters
• 出版年：2017
• 出版时间：February 2017
• 年：2017
• 卷：43
• 期：2
• 页码：75-105
• 全文大小：
• 刊物类别：Physics and Astronomy
• 刊物主题：Astronomy, Observations and Techniques; Astrophysics and Astroparticles;
• 出版者：Pleiades Publishing
• ISSN：1562-6873
• 卷排序：43

文摘

We have checked the existence of a zone of avoidance oriented along the Galactic rotation axis in the globular cluster (GC) system of the Galaxy and performed a parametrization of this zone in the axisymmetric approximation. The possibility of the presence of such a structure in the shape of a double cone has previously been discussed in the literature. We show that an unambiguous conclusion about the existence of an axial zone of avoidance and its parameters cannot be reached based on the maximization of the formal cone of avoidance due to the discreteness of the GC system. The ambiguity allows the construction of the representation of voids in the GC system by a set of largest-radius meridional cylindrical voids to be overcome. As a result of our structural study of this set for northern and southern GCs independently, we have managed to identify ordered, vertically connected axial zones of avoidance with similar characteristics. Our mapping of the combined axial zone of avoidance in the separate and joint analyses of the northern and southern voids shows that this structure is traceable at |Z| ≳ 1 kpc, it is similar in shape to a double cone whose axis crosses the region of greatest GC number density, and the southern cavity of the zone has a less regular shape than the northern one. By modeling the distribution ofGalactocentric latitudes forGCs, we have determined the half-angle of the cone of avoidance α₀ = 15◦. 0_{−4◦. 1}+2◦. 1 and the distance to the Galactic center R₀ = 7.3 ± 0.5 kpc (in the scale of the Harris (1996) catalog, the 2010 version) as the distance from the Sun to the point of intersection of the cone axis with the center–anticenter line. A correction to the calibration of the GC distance scale obtained in the same version of the Harris catalog from Galactic objects leads to an estimate of R₀ = 7.2±0.5|_stat ±0.3|_calib kpc. The systematic error in R₀ due to the observational incompleteness of GCs for this method is insignificant. The probability that the zone of avoidance at the characteristics found is random in nature is ≤2%. We have revealed evidence for the elongation of the zone of avoidance in the direction orthogonal to the center–anticenter axis, which, just as the north–south difference in this zone, may be attributable to the influence of the Magellanic Clouds. The detectability of similar zones of avoidance in the GC systems of external galaxies is discussed.