Searching for mass-spin correlations in the population of
  gravitational-wave events: the GWTC-3 case study
  One fundamental goal of the newly born gravitational wave astronomy is
discovering the origin of the observed binary black hole mergers. Towards this
end, identifying features in the growing wealth of data may help in
distinguishing different formation pathways. While large uncertainties still
affect the binary formation models, spin-mass relations remain characteristic
features of specific classes of channels. By focusing on the effective inspiral
spin $\chi_{\rm eff}$, the best reconstructed spin-related merger parameter, we
show that current GWTC-3 data support the hypothesis that a fraction of events
may display mass-spin correlations similar to the one produced by dynamical
formation channels, either them being of astrophysical or primordial nature. We
quantify the Bayesian evidence in favour of those models, which are
substantially preferred when compared to the Gaussian phenomenological model
adopted to describe the distribution of $\chi_{\rm eff}$ in the recent
LIGO/Virgo/KAGRA population analyses.
