The time delay distribution and formation metallicity of LIGO-Virgo's binary black holes

Understand

We derive the first constraints on the time delay distribution of binary black hole (BBH) mergers using the LIGO-Virgo Gravitational-Wave Transient Catalog GWTC-2.

• Assuming that the progenitor formation rate follows the star formation rate (SFR), the data favor that $43$--$100\%$ of mergers have delay times $<4.5$ Gyr (90% credibility).
• Adopting a model for the metallicity evolution, we derive joint constraints for the metallicity-dependence of the BBH formation efficiency and the distribution of time delays between formation and merger.
• Short time delays are favored regardless of the assumed metallicity dependence, although the preference for short delays weakens as we consider stricter low-metallicity thresholds for BBH formation.