Halo occupation distribution (HOD) modelling of high redshift galaxies using the BlueTides simulation

We construct halo occupation distribution (HOD) models of high redshift (z 7.5) galaxies with M*>10⁸~M_/h using the BlueTides hydrodynamic simulation suite, with a particular emphasis on modelling the small scale / 1-halo clustering (0.01 r 1~ h⁻¹Mpc). Similar to low redshift studies, we find that the central and satellite mean HODs (<Ncen> and <Nₛₐₜ>) can be modeled by a smoothed step function and a power law respectively. The number density of satellite galaxies is however significantly suppressed compared to low redshift (satellite fractions drop from ~ 50 % at $z=0$ to 10 % at $z=7.5$). The mean number of satellites, <Nₛₐₜ> < 1 for halo masses below 3 × 10¹¹ M_/h (a rare halo at these redshifts). For the radial number density profiles, satellites with 10⁸ M^* 10⁹ M_/h in halos with MH 3 ×10¹¹ M_/h are consistent with NFW (with concentrations cₛₐₜ ~ 10-40). Within halos of mass MH 3 × 10¹¹ M_/h satellites exhibit a power law profile with slope -3. Because these halos dominate the small scale clustering, the resulting 1-halo term is steeper than predicted using standard NFW profiles. Using this power-law profile for satellites, we can successfully reproduce the small-scale clustering exhibited by BlueTides galaxies using HOD modelling. We predict the highest probability of detecting satellites at $z>7.5$ is around centrals of M^*~ 3 × 10¹⁰ M_/h (with M* a few 10⁷ M_/h ). This should be achievable with the James Webb Space Telescope (JWST).