Black Hole Mergers of AGN Origin in LIGO–Virgo’s O1–O3a Observing Periods

The origin of the black hole mergers detected by LIGO–Virgo remains an open question. While the unusual mass and spin of a few events constrain their possible astrophysical formation mechanisms, it is difficult to classify the bulk of the observed mergers. Here we consider the distribution of masses and spins in LIGO–Virgo's first two observing catalogs. We show that, for black holes in the mass gap, our fiducial active galactic nucleus (AGN) model is preferred over a parametric mass–spin model fit to the full GWTC-2 merger sample (Bayes factor ${ \mathcal B }\gt 10$). This preference, nevertheless, depends on uncertain AGN model parameters. We further show that a 20% fractional contribution of the detected events of an AGN-disk origin reproduces well the observed black hole mass distribution in the pair-instability mass gap, while only marginally contributing to the lower-mass detected population. The overall AGN contribution corresponds to a black hole merger rate of about 2.5 Gpc−3 yr−1, comparable to theoretical expectations.