The angular momentum of cold dark matter haloes with and without baryons
The angular momentum of cold dark matter haloes with and without baryons
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DOI：
10.1111/j.1365-2966.2010.16368.x
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发表时间：
2009-06
影响因子：
4.8
通讯作者：
P. Bett;V. Eke;C. Frenk;A. Jenkins;Takashi Okamoto Institute for Computational Cosmology-Takashi-Okamoto-Institute-for-Computational-102817220;U. Durham;UK.
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文献类型：
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作者：
P. Bett;V. Eke;C. Frenk;A. Jenkins;Takashi Okamoto Institute for Computational Cosmology-Takashi-Okamoto-Institute-for-Computational-102817220;U. Durham;UK.
我们调查的幅度和内部对齐的冷暗物质晕的角动量在模拟和没有重子。我们分析了Springel等人的Millennium模拟中以及一个较小但分辨率更高的模拟中数十万个良好分辨的晕的累积角动量分布，总共跨越5个数量级。对于给定质量的晕，比角动量的中值随半径的增大而增大，其值为j（6 r）/ r。矢量的方向随半径变化很大：内（. 0.25Rvir）和总的（6 Rvir）角动量矢量约为25 π。为了研究重子对晕自旋的影响，我们采用了另一种高分辨率的模拟方法，包括气体冷却、星形成和反馈。这个模拟产生了一个星系样本，具有真实的盘与总比D/T：三分之二的星系在B波段D/T > 0.5。星系的形成使暗物质在0.1Rvir内旋转，使得特定的晕角动量在中值中增加了50%。暗物质的角动量变得更好地对齐，但在晕和中央星系之间仍然存在广泛的（错误）对齐分布，它们的角动量之间的夹角为30度。相对于晕的形状，星系的取向有一个范围：其中一半的星系的短轴偏离超过45 °，尽管只有大约10%的星系位于垂直于晕长轴的平面的30 °以内。最后，我们根据星系的方向排列了一个晕样本，并将投影的质量分布进行了叠加。虽然个别的晕是明显的非球面，星系晕的错位产生了一个堆叠的质量分布，不能从圆形区分。如果在我们的模拟中发现的缺乏对齐是现实的，那么弱透镜研究使用这种技术测量冷暗物质晕的椭圆率将是非常困难的。
We investigate the magnitude and internal alignment of the angular momentum of cold dark matter haloes in simulations with and without baryons. We analyse the cumulative angular momentum profiles of hundreds of thousands of well resolved h aloes in the Millennium simulation of Springel et al. and in a smaller, but higher resolu tion, simulation, in total spanning 5 orders of magnitude in mass. For haloes of a given mass, the median specific angular momentum increases with radius as j(6 r) / r. The direction of the vector varies considerably with radius: the median angle between the inner (. 0.25Rvir) and total (6 Rvir) angular momentum vectors is about 25 ◦ . To investigate how baryons affect halo spin, we use another high-resolution simulation, which includes gas cooling, s tar formation and feedback. This simulation produces a sample of galaxies with a realistic di stribution of disc-to-total ratios, D/T : two thirds of the galaxies have D/T > 0.5 in the B-band. The formation of the galaxy spins up the dark matter within 0.1Rvir such that the specific halo angular momentum increases by � 50 per cent in the median. The dark matter angular momentum becomes better aligned, but there remains a broad distribution of (mis-)al ignments between the halo and the central galaxy, with a median angle between their angular momenta of � 30 ◦ . Galaxies have a range of orientations relative to the shape of the halo: hal f of them have their minor axes misaligned by more than 45 ◦ , although only about 10 per cent of the galaxies lie within 30 ◦ of the plane perpendicular to the major axis of their halo. Fi nally, we align a sample of haloes according to the orientation of their galaxies and stack the projected mass distributions. Although the individual haloes are significantly aspherical, galaxy‐halo misalignments produce a stacked mass distribution that cannot be distinguished fr om circular. If the lack of alignment found in our simulations is realistic, it will be extremely d ifficult for weak lensing studies to measure the ellipticity of cold dark matter haloes using thi s technique.