Triple and quadruple black holes in the ASTRID simulation at <i>z</i> ∼ 2

We use the ASTRID cosmological hydrodynamic simulation to investigate properties and evolution of triple quadruple Massive Black Hole (MBH) systems at $z = 2-3$. Only a handful MBH tuple have been detected date. In ASTRID, we find $4\%$ $M_{\rm BH}>10^7\,M_\odot$ are in tuples with $\Delta r_{\rm max} < 200\,{\rm kpc}$. The span range separations majority observable AGN r \sim 50-100$ kpc. They include some most massive BHs (up $10^{10} \,M_\odot$) but least one components BH} 10^7 \,M_\odot$. Tuples' host galaxies typically $M_* 10^{10-11} that $>10\%$ halos halo} > 10^{13} M_\odot$ tuples. Following subsequent interactions between MBHs tuples, found $\sim 5\%$ triplets all three merge within Gyr, $15\%$ go through merger. As by-product complex multi-galaxy interaction these systems, also up lead runaway MBHs. virtually ultramassive black holes ($>10^{10} \,M_\odot $) undergone quasar phase while for 10^9 \,M_\odot$ this fraction drops $50\%$.