Multiple regimes and coalescence timescales for massive black hole pairs ; the critical role of galaxy formation physics

Understand

We discuss the latest results of numerical simulations following the orbital decay of massive black hole pairs in galaxy mergers.

• We highlight important differences between gas-poor and gas-rich hosts, and between orbital evolution taking place at high redshift as opposed to low redshift.
• Two effects have a huge impact and are rather novel in the context of massive black hole binaries.
• The first is the increase in characteristic density of galactic nuclei of merger remnants as galaxies are more compact at high redshift due to the way dark halo collapse depends on redshift.