Can the Steep Mass Profile of A1689 Be Explained by a Triaxial Dark Halo?
Can the Steep Mass Profile of A1689 Be Explained by a Triaxial Dark Halo?
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DOI：
10.1086/452629
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发表时间：
2005-05
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影响因子：
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通讯作者：
M. Oguri;M. Takada;K. Umetsu;T. Broadhurst
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作者：
M. Oguri;M. Takada;K. Umetsu;T. Broadhurst
从最近详细的透镜观测中得出的A1689的陡峭质量分布与标准冷暗物质（CDM）模型预测的低浓度晕不容易调和。然而，光晕三轴性可能会对假设球对称质量分布的轮廓约束产生偏差，因为透镜效应只与投影质量分布有关。一定程度的光晕三轴性是CDM结构形成所固有的，源于暗物质的无碰撞性质。在这里，我们将基于cdm的三轴晕模型预测与基于哈勃太空望远镜先进巡天相机和斯巴鲁数据的A1689的精确透镜测量结果进行了比较，在10 kpc > r > 2 Mpc的宽范围内。模型透镜剖面覆盖了光晕质量和形状（浓度和三轴性）的固有分布，并在与数据比较时在所有倾角上进行投影。我们发现模型参数只有弱约束和强简并，这主要是由于缺乏沿视线的信息。特别是，随着三轴性的增加，浓度参数的限制越来越少。然而，通过将获得的约束条件与数值模拟计算的轴比和浓度参数的期望概率分布进行比较，我们发现CDM模型中约6%的星团大小的光晕可以在2 σ水平上与A1689透镜观测结果匹配，对应于光晕长轴与视线对准的情况。因此，光晕三轴性可以减少理论与观测之间的明显差异。这一假设需要通过对其他星团的统计透镜研究，以及利用x射线、运动学和Sunyaev-Zel'dovich效应观测得出的互补三维信息来进一步探索。
The steep mass profile of A1689 derived from recent detailed lensing observations is not readily reconciled with the low-concentration halos predicted by the standard cold dark matter (CDM) model. However, halo triaxiality may act to bias the profile constraints derived assuming a spherically symmetric mass distribution, since lensing relates only to the projected mass distribution. A degree of halo triaxiality is inherent to the CDM structure formation, arising from the collisionless nature of the dark matter. Here we compare the CDM-based model predictions of triaxial halo with the precise lensing measurements of A1689 based on the Advanced Camera for Surveys Hubble Space Telescope and Subaru data, over a wide range of 10 kpc ≲ r ≲ 2 Mpc. The model lensing profiles cover the intrinsic spread of halo mass and shape (concentration and triaxiality) and are projected over all inclinations when comparing with the data. We show that the model parameters are only weakly constrained and strongly degenerate mainly because of the lack of information along the line of sight. In particular, the limits on the concentration parameter become less restrictive with increasing triaxiality. Yet, by comparing the obtained constraints with expected probability distributions for the axis ratio and concentration parameters computed from numerical simulations, we find that ~6% of cluster-size halos in the CDM model can match the A1689 lensing observations at the 2 σ level, corresponding to cases in which the major axis of the halo is aligned with the line of sight. Thus, halo triaxiality could reduce the apparent discrepancy between theory and observation. This hypothesis needs to be further explored by a statistical lensing study for other clusters, as well as by complementary three-dimensional information derived using X-ray, kinematics, and Sunyaev-Zel'dovich effect observations.