http://arxiv.org/abs/2004.00863
The impact of the streaming motion between gas and dark matter on the first structure formation has been actively explored by recent studies. Here we investigate how much the key results are affected by two approximations made in many of those studies. One is to implement the streaming motion by accounting for only the relative velocity between baryons and dark matter while assuming “baryons trace dark matter” spatially at the initial conditions of the simulation. This assumption neglects the impact on the gas density taking place before the initialization. In our simulation initialized at $z=200$, this approximation overestimates the gas power spectrum up to 30\% at $k\approx10^2~h~\mbox{Mpc}^{-1}$ at $z=20$. However, the halo mass function and the gas fraction in halos are minimally affected. The other approximation is to artificially amplify the density/velocity fluctuations in a cosmic mean density volume at the initialization to simulate the first minihalos. This approximation gives a head start to the halo growth and the subsequent growth rate is as fast as in the mean density. The growth in actual overdensity, however, is accelerated gradually in time. For example, increasing $\sigma_8$ by 50\% effectively transforms $z\rightarrow\sqrt{1.5}z$ in the halo mass growth history while in 2-$\sigma$ overdensity the acceleration is described by $z\rightarrow{z}+4.8$. Halos in the former case are more grown than in the latter before $z\approx27$ and vice versa after. The gas fraction in halo remains unchanged by this second approximation as well, suggesting that those approximations do {\it{not}} bias the PopIII star-formation rate significantly.
H. Park, K. Ahn, N. Yoshida, et. al.
Fri, 3 Apr 20
44/62
Comments: Submitted to ApJ