Influence of baryons on spatial distribution of matter: higher order   correlation functions
  Baryonic physical processes could leave non-negligible imprint on cosmic matter distribution pattern. Series of high precision simulation data sets with identical initial condition are employed for count-in-cell (CIC) analysis, including one N-body dark matter run, one with adiabatic gas only and one with dissipative processes. Variances and higher order correlation functions of dark matter and gas are estimated. It is found that baryon physical processes mainly affected dark matter distribution at scales less than $1h^{-1}$Mpc. In comparison with the pure dark matter run, adiabatic process alone strengthens variance of dark matter by \sim 10% at scale $0.1h^{-1}$Mpc, while $S_n$s of dark matter deviate from pure dark matter case only mildly at a few percentages. Dissipative gas run does not differ much to the adiabatic run in dark matter variance, but renders significantly different $S_n$ parameters of dark matter, bringing about more than 10% enhancement to $S_3$ at $0.1h^{-1}$Mpc and $z=0$. Distribution patterns of gas in two hydrodynamical simulations are prominently different. Variance of gas at $z=0$ decreases by $\sim 30%$ in adiabatic simulation while by $\sim 60%$ in non-adiabatic simulation at $0.1h^{-1}$Mpc, the attenuation is weaker at larger scales but still obvious at $\sim 10h^{-1}$Mpc. $S_n$ parameters of gas are biased upward at scales $< \sim 4h^{-1}$Mpc, dissipative processes give $\sim 84%$ promotion at $z=0$ to $S_3$ at $0.1h^{-1}$Mpc against the moderate $\sim 7%$ in adiabatic simulation. The clustering segregation we observed between gas and dark matter could have intricate implication on modeling galaxy distribution and relevant cosmological application demanding fine details of matter distribution in strongly nonlinear regime. 
Xiaojun Zhu (PMO) and Jun Pan (NAOC)
astro-ph.CO