Abstract Physical processes involving baryons could leave a non-negligible imprint on the distribution of cosmic matter. A series of simulated data sets at high resolution with identical initial conditions are employed for count-in-cell analysis, including one N-body pure dark matter run, one with only adiabatic gas and one with dissipative processes. Variances and higher order cumulants Sn of dark matter and gas are estimated. It is found that physical processes with baryons mainly affect distributions of dark matter at scales less than 1 h−1 Mpc. In comparison with the pure dark matter run, adiabatic processes alone strengthen the variance of dark matter by ~10% at a scale of 0.1 h−1 Mpc, while the Sn parameters of dark matter only mildly deviate by a few percent. The dissipative gas run does not differ much from the adiabatic run in terms of variance for dark matter, but renders significantly different Sn parameters describing the dark matter, bringing about a more than 10% enhancement to S3 at 0.1 h−1 Mpc and z = 0 and being even larger at a higher redshift. Distribution patterns of gas in two hydrodynamical simulations are quite different. Variance of gas at z = 0 decreases by ~30% in the adiabatic simulation but by ~60% in the non-adiabatic simulation at 0.1 h−1 Mpc. The attenuation is weaker at larger scales but is still obvious at ~10 h−1 Mpc. Sn parameters of gas are biased upward at scales < ~4 h−1 Mpc, and dissipative processes show an ~84% promotion at z = 0 to S3 at 0.1 h−1 Mpc in contrast with the ~7% change in the adiabatic run. The segregation in clustering between gas and dark matter could have dramatic implications on modeling distributions of galaxies and relevant cosmological applications demanding fine details of matter distribution in a strongly nonlinear regime.

Keywords cosmology: dark matter — large-scale structure of universe — methods: statistical

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