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摘要
A long-standing issue in peculiar velocity cosmology is whether the halo/galaxy velocity bias b(v) = 1 at large scale. The resolution of this important issue must resort to high-precision cosmological simulations. However, this is hampered by another long-standing "sampling artifact" problem in volume-weighted velocity measurement. We circumvent this problem with a hybrid approach. We first measure the statistics free of sampling artifacts, then link them to volume-weighted statistics in theory, and finally solve for the velocity bias. b(v) (determined by our method) is not only free of sampling artifacts but also free of cosmic variance. We apply this method to Lambda CDM N-body simulation of 3072(3) particles and 1200 Mpc/h box size. For the first time, we determine the halo velocity bias to 0.1%-1% accuracy. Our major findings are as follows: (1) b(v) not equal 1 at k > 0.1 h/Mpc. The deviation from unity (vertical bar b(v)-1 vertical bar) increases with k. Depending on halo mass and redshift, it may reach O(0.01) at k = 0.2 h/Mpc and O(0.05) at k similar to 0.3 h/Mpc. The discovered b(v) not equal 1 has a statistically significant impact on the structure growth rate measurement by spectroscopic redshift surveys, including DESI, Euclid, and SKA. (2) Both the sign and the amplitude of b(v) - 1 depend on mass and redshift. These results disagree with the peak model prediction in that bv has much weaker deviation from unity, varies with redshift, and can be bigger than unity. (3) Most of the mass and redshift dependences can be compressed into a single dependence on the halo density bias. Based on this finding, we provide an approximate two-parameter fitting formula.
- 出版日期2018-7-1
- 单位上海交通大学
