HOD modelling of high redshift galaxies using the BLUETIDES simulation

We construct halo occupation distribution (HOD) models of high redshift ($z \gtrsim 7.5$)galaxieswith$M_{*}>10^8~M_{\odot}/h$ using the BlueTides hydrodynamic simulation suite, with a particular emphasis on modelling the small scale / 1-halo clustering ($0.01\lesssim r\lesssim 1h^{-1}\mathrm{M}\mathrm{p}\mathrm{c}$). Similar to low redshift studies, we find that the central and satellite mean HODs ($<N_{\mathrm{c}\mathrm{e}\mathrm{n}}>$ and $<N_{\mathrm{s}\mathrm{a}\mathrm{t}}>$) 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 $\sim 50\mathrm{\%}$ at $z=0$ to $\lesssim 10 %$at$z=7.5$)\mathrm{.}Themeannumberofsatellites,$\left<N_{$\mathrm{s}\mathrm{a}\mathrm{t}$}\right> < 1$forhalomassesbelow$3 \times 10^{11} M_{\odot}/h$ (a rare halo at these redshifts). For the radial number density profiles, satellites with ${10}^8\lesssim M^{\ast }\lesssim {10}^9{M}_{\odot }\mathrm{/}h$ in halos with $M_H\gtrsim 3\times {10}^{11}{M}_{\odot }\mathrm{/}h$ are consistent with NFW (with concentrations $c_{\mathrm{s}\mathrm{a}\mathrm{t}}\sim 10-40$). Within halos of mass $M_H\lesssim 3\times {10}^{11}{M}_{\odot }\mathrm{/}h$ 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 $M^{\ast }\sim 3\times {10}^{10}{M}_{\odot }\mathrm{/}h$ (with $M^{\ast }\gtrsim$ a few ${10}^7{M}_{\odot }\mathrm{/}h$ ). This should be achievable with the James Webb Space Telescope (JWST).