SURFS: Riding the waves with Synthetic UniveRses For Surveys

We present the Synthetic UniveRses For Surveys ({\sc surfs}) simulations, a set of N-body/Hydro simulations of the concordance $\mathrm{\Lambda }$ Cold Dark Matter (\LCDM) cosmology. These simulations use Planck cosmology, contain up to 10 billion particles and sample scales & halo masses down to $1$kpc & $10^8{\rm M}\odot$\mathrm{.}Weidentifyandtrackhaloesfrom$z=24$ to today using a state-of-the-art 6D halo finder and merger tree builder. We demonstrate that certain properties of halo merger trees are numerically converged for haloes composed of $\gtrsim 100$ particles. Haloes smoothly grow in mass, $V{\rm max}$,withthemasshistorycharacterisedby$\log M(a)\propto\exp\left[-(a/\beta)^\alpha\right]$where$a$isthescalefactor,$\alpha(M)\approx0.8$\mathrm{\&}$\beta(M)\approx0.024$, with these parameters decreasing with decreasing halo mass. Subhaloes follow power-law cumulative mass and velocity functions, i.e. $n(>f)\propto f^{-\alpha }$ with ${\alpha }_M=0.83\pm 0.01$ and ${\alpha }_{V_{\mathrm{m}\mathrm{a}\mathrm{x}}}=2.13\pm 0.03$ for mass & velocity respectively, independent of redshift, as seen in previous studies. The halo-to-halo scatter in amplitude is $0.9$~dex. The number of subhaloes in a halo weakly correlates with a halo’s concentration $c$ & spin $\lambda$:haloes of high $c$ & low $\lambda$ have $60\mathrm{\%}$ more subhaloes than similar mass haloes of low $c$ & high $\lambda$. High cadence tracking shows subhaloes are dynamic residents, with $25\mathrm{\%}$ leaving their host halo momentarily, becoming a backsplash subhalo, and another $20\mathrm{\%}$ changing hosts entirely, in agreement with previous studies. In general, subhaloes have elliptical orbits, $e\approx 0.6$, with periods of $2.3_{-1.7}^{+2.1}$~Gyrs. Subhaloes lose most of their mass at pericentric passage with mass loss rates of $\sim 40\mathrm{\%}$~Gyr${}^{-1}$. These catalogues will be made publicly available.