Investigating the mixing between two black hole populations in LIGO-Virgo-KAGRA GWTC-3

We introduce a population model to analyze the mixing between hypothesised power-law and ~ 35 M_ Gaussian bump black hole populations in the latest gravitational wave catalog, GWTC-3, estimating their co-location and separation. We find a relatively low level of mixing, 3.1+5.0-3.1%, between the power-law and Gaussian populations, compared to the percentage of mergers containing two Gaussian bump black holes, 5.0+3.2-1.7%. Our analysis indicates that black holes within the Gaussian bump are generally separate from the power-law population, with only a minor fraction engaging in mixing and contributing to the M ~ 14 M_ peak in the chirp mass. This leads us to identify a distinct population of Binary Gaussian Black Holes (BGBHs) that arise from mergers within the Gaussian bump. We suggest that current theories for the formation of the massive 35 M_ Gaussian bump population may need to reevaluate the underlying mechanisms that drive the preference for BGBHs.