Hierarchical black hole mergers in young, globular and nuclear star clusters: the effect of metallicity, spin and cluster properties

ABSTRACT We explore hierarchical black hole (BH) mergers in nuclear star clusters (NSCs), globular (GCs) and young (YSCs), accounting for both original dynamically assembled binary BHs (BBHs). find that the median mass of first- nth-generation dynamical is larger GCs YSCs with respect to NSCs because lighter are ejected by supernova kicks from lower clusters. Also, BH masses strongly affected metallicity progenitor stars: primary a merger ?24–38 M? (?9–15 M?) metal-poor (metal-rich) NSCs. The maximum mainly depends on escape velocity: up several thousand form NSCs, while host hundred M?. Furthermore, we calculate fraction at least one component pair-instability gap (fPI) intermediate-mass regime (fIMBH). In fiducial model BBHs Z = 0.002, fPI ? 0.05, 0.02 0.007 (fIMBH 0.01, 0.002 0.001) YSCs, respectively. Both fIMBH drop order magnitude solar metallicity. Finally, investigate formation GW190521 assuming it either nearly equal-mass BBH or an ratio inspiral.