科研之友
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摘要
A profound assumption in peculiar velocity cosmology is b(v) = 1 at sufficiently large scales, where bv is the volume-weighted halo(galaxy) velocity bias with respect to the matter velocity field. However, this fundamental assumption has not been robustly verified in numerical simulations. Furthermore, it is challenged by structure formation theory (Bardeen, Bond, Kaiser and Szalay, Astrophys. J. 304, 15 (1986); Desjacques and Sheth, Phys. Rev D 81, 023526 (2010), which predicts the existence of velocity bias (at least for proto-halos) due to the fact that halos reside in special regions (local density peaks). The major obstacle to measuring the volume-weighted velocity from N-body simulations is an unphysical sampling artifact. It is entangled in the measured velocity statistics and becomes significant for sparse populations. With recently improved understanding of the sampling artifact (Zhang, Zheng and Jing, 2015, PRD; Zheng, Zhang and Jing, 2015, PRD), for the first time we are able to appropriately correct this sampling artifact and then robustly measure the volume-weighted halo velocity bias. (1) We verify b(v) = 1 within 2% model uncertainty at k less than or similar to 0.1 h/Mpc and z = 0-2 for halos of mass similar to 10(12)-10(13) h(-1) M-circle dot and, therefore, consolidate a foundation for the peculiar velocity cosmology. (2) We also find statistically significant signs of bv. 1 at k greater than or similar to 0.1 h/Mpc. Unfortunately, whether this is real or caused by a residual sampling artifact requires further investigation. Nevertheless, cosmology based on the k greater than or similar to 0.1 h/Mpc velocity data should be careful with this potential velocity bias.
- 出版日期2015-6-9
- 单位上海交通大学; 中国科学院上海天文台
