  Observations of gravitational waves (GWs) from merging compact binaries have
become a regular occurrence. The continued advancement of the LIGO-Virgo-KAGRA
(LVK) Collaboration detectors have now produced a catalog of over 90 such
mergers, from which we can begin to uncover the formation history of merging
compact binaries. In this work, we search for subpopulations in the LVK's third
gravitational wave transient catalog (GWTC-3) by incorporating discrete latent
variables in the hierarchical Bayesian inference framework to probabilistically
assign each BBH observation into separate categories associated with distinctly
different population distributions. By incorporating formation channel
knowledge within the mass and spin correlations found in each category, we find
an over density of mergers with a primary mass of $\sim10 M_\odot$, consistent
with isolated binary formation. This low-mass subpopulation has a spin
magnitude distribution peaking at $a_\mathrm{peak}=0.16^{0.19}_{-0.16}$,
exhibits spins preferentially aligned with the binary's orbital angular
momentum, is constrained by $15^{+0.0}_{-1.0}$ of our observations, and
contributes $82\%^{+8.0\%}_{-16\%}$ to the overall population of BBHs.
Additionally, we find that the component of the mass distribution containing
the previously identified $35M_\odot$ peak has spins consistent with the
$10M_\odot$ events, with $99\%$ of primary masses less than $m_{1,99\%} =
49^{+25}_{-8.1} M_\odot$, providing an estimate of the lower edge of the
theorized pair instability mass gap. This work is a first step in gaining a
deeper understanding of compact binary formation and evolution, and will
provide more robust conclusions as the catalog of observations becomes larger.
