Implications of recoil kicks for black hole mergers from LIGO/Virgo catalogs

The first and second Gravitational Wave Transient Catalogs by the LIGO/Virgo Collaboration include 50 confirmed merger events from the first, second, and first half of the third observational runs. We compute the distribution of recoil kicks imparted to the merger remnants and estimate their retention probability within various astrophysical environments as a function of the maximum progenitor spin (X-max), assuming that the LIGO/Virgo binary black hole (BBH) mergers were catalyzed by dynamical assembly in a dense star cluster. We find that the distributions of average recoil kicks are peaked at about 150 km s(-1), 250 km s(-1), 350 km s(-1), 600 km s(-1), for maximum progenitor spins of 0.1, 0.3, 0.5, 0.8, respectively. Only environments with escape speed greater than or similar to 100 km s(-1), as found in galactic nuclear star clusters as well as in the most massive globular clusters and super star clusters, could efficiently retain the merger remnants of the LIGO/Virgo BBH population even for low progenitor spins (X-max = 0.1). In the case of high progenitor spins (X-max greater than or similar to 0.5), only the most massive nuclear star clusters can retain the merger products. We also show that the estimated values of the effective spin and of the remnant spin of GW170729, GW190412, GW190519_153544, and GW190620_030421 can be reproduced if their progenitors were moderately spinning (X-max greater than or similar to 0.3), while for GW190517_055101 if the progenitors were rapidly spinning (X-ma(x) greater than or similar to 0.8). Alternatively, some of these events could be explained if at least one of the progenitors is already a second-generation BH, originated from a previous merger.

Automated summary

The study estimated the distribution of recoil kicks imparted to merger remnants in gravitational wave events and determined their retention probability in various astrophysical environments depending on the maximum progenitor spin. The results show that only environments with escape speeds greater than or equal to 100 km/s can efficiently retain the remnants of LIGO/Virgo BBH mergers.