Direct Mapping of Massive Compact Objects in Extragalactic Dark Halos
Direct Mapping of Massive Compact Objects in Extragalactic Dark Halos
复制标题
河外暗晕中巨大致密天体的直接测绘
DOI：
10.1086/377247
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发表时间：
2003
期刊：
影响因子：
--
通讯作者：
M. Chiba
中科院分区：
文献类型：
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作者：
K. T. Inoue;M. Chiba
在星系晕中，相当一部分的非重子或重子暗物质可能由质量M = 101-104 M的大质量致密天体（MASCO）组成。这种致密天体的可能候选者包括原始黑洞或原始（第三星族）恒星的残余。我们提出了一种直接探测河外晕中MASCOs的方法，使用VLBI技术，具有极高的分辨率，将实现下一代的VLBI空间天文台计划，如VSOP-2的使命。如果一个星系晕包含了大量的MASCOs产生多个图像的背景射电大声类星体的引力透镜，那么高分辨率的射电地图的每个macrolensed图像应该揭示微透镜效应的MASCOs。为了评估它们的观测可行性，我们模拟了射电大声，四图像透镜类星体，B1422+231，假设角分辨率为~0.01质量。MASCO由点质量表示。为了比较，我们还用奇异等温球模拟了B1422+231的微透镜效应。我们发现，表面亮度的宏透镜图像显示出不同的空间模式的爱因斯坦半径的规模上的扰动。在点质量扰动的情况下，许多微小的暗点也出现在宏观透镜图像中，这与原始类星体图像边缘的表面亮度下降有关，而SIS模型中没有这样的斑点。由于每个宏透镜图像中的此类空间图案如果与透镜扰动相关，则无法线性映射到其他宏透镜图像中的空间图案，因此将它们与类星体内的固有子结构区分开来相当容易。根据大小，位置和放大或缩小的图像模式，我们将能够确定单个MASCO的质量和密度分布以及其在星系晕中的空间分布和丰度。
A significant fraction of nonbaryonic or baryonic dark matter in galactic halos may consist of massive compact objects (MASCOs) with mass M = 101-104 M☉. Possible candidates for such compact objects include primordial black holes or remnants of primordial (Population III) stars. We propose a method for directly detecting MASCOs in extragalactic halos, using the VLBI techniques with extremely high resolution that would be achieved by the next-generation mission of the VLBI Space Observatory Program such as VSOP-2. If a galactic halo comprising a large number of MASCOs produces multiple images of a background radio-loud QSO by gravitational lensing, then a high-resolution radio map of each macrolensed image should reveal microlensing effects by MASCOs. To assess their observational feasibility, we simulate microlensing of the radio-loud, four-image lensed QSO, B1422+231, assuming angular resolution of ~0.01 mas. MASCOs are represented by point masses. For comparison, we also simulate microlensing of B1422+231 by singular isothermal spheres. We find that the surface brightness of the macrolensed images shows distinct spatial patterns on the scale of the Einstein radius of the perturbers. In the case of point-mass perturbers, many tiny dark spots also appear in the macrolensed images associated with a decrease in the surface brightness toward the fringe of the original QSO image, whereas no such spots are available in the SIS models. Because such spatial patterns in each macrolensed image cannot be linearly mapped to those in other macrolensed images if they are relevant to lensing perturbers, it is fairly easy to discriminate them from intrinsic substructures within a QSO. Based on the size, position, and magnified or demagnified patterns of images, we shall be able to determine the mass and density profile of an individual MASCO as well as its spatial distribution and abundance in a galactic halo.