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arXiv 2104.02160astro-ph.GA
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并合晕轨道参数分布的成因

The Origin of the Orbital Parameter Distribution of Merging Halos

A. J. Benson

摘要:

我们描述了一个简单的模型,它解释了合并对的暗物质晕的轨道速度分布的定性和(近似)定量特征。我们的模型认为,一个主要的暗物质晕作为一个扰动的二次晕的速度描述的线性理论的背景。通过计算扰动晕的“损失锥”内轨道上的次级晕的集合,我们得到了这些捕获的晕的轨道参数的分布。该模型能够为从N体模拟测量的该分布的特征提供定性解释,并且与这些测量结果大致定量一致。由于背景晕的速度色散在较小的尺度上较大,我们的模型预测合并晕的特征速度相对于这些晕的维里速度在较低质量系统中总体增加。我们的模型也提供了一个简单的解释,当考虑在固定的峰高时,测量的轨道速度分布函数的红移的独立性。通过将轨道参数分布与基础功率谱相联系,我们的模型还允许对修改功率谱的影响进行估计,例如通过在大波数处进行截断。对于可信的暖暗物质模型,我们发现这种截断对预测的分布只有很小的影响。

英文摘要:

We describe a simple model which explains the qualitative and (approximate) quantitative features of the distribution of orbital velocities of merging pairs of dark matter halos. Our model considers a primary dark matter halo as a perturber in a background of secondary halos with velocities described by linear theory. By evaluating the ensemble of secondary halos on orbits within the perturbing halo's "loss cone" we derive the distribution of orbital parameters of these captured halos. This model is able provide qualitative explanations for the features of this distribution as measured from N-body simulations, and is in approximate quantitative agreement with those measurements. As the velocity dispersion of the background halos is larger on smaller scales our model predicts an overall increase in the characteristic velocities of merging halos, relative to the virial velocities of those halos, in lower mass systems. Our model also provides a simple explanation for the measured independence of the orbital velocity distribution function on redshift when considered at fixed peak height. By connecting the orbital parameter distribution to the underlying power spectrum our model also allows for estimates to be made of the effect of modifying that power spectrum, for example by including a truncation at large wavenumber. For plausible warm dark matter models we find that this truncation has only a small effect on the predicted distributions.

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