Effective spin distribution of black hole mergers in triples

Many astrophysical scenarios have been proposed to explain the several black hole (BH) and neutron star binary mergers observed via gravitational waves (GWs) by the LIGO-Virgo collaboration. Contributions from various channels can be statistically disentangled by mass, spin, eccentricity and redshift distributions of merging binaries. In this paper, we investigate the signatures of BH-BH binary mergers induced by a third companion through the Lidov-Kozai mechanism in triple systems. We adopt different prescriptions for the supernovae natal kicks and consider different progenitor metallicities and initial orbital parameters. We show that the typical eccentricity in the LIGO band is $0.01$-$0.1$ and that the merger rate is in the range $0.008-9 \ \mathrm{Gpc}^{-3}\ \mathrm{yr}^{-1}$, depending on the natal kick prescriptions and progenitor metallicity. Furthermore, we find that the typical distribution of effective projected spin is peaked at $\chi_{\rm eff}\sim 0$ with significant tails. We show that the triple scenario could reproduce the distribution of $\chi_{\rm eff}$. We find that the triple channel may be strongly constrained by the misalignment angle between the binary component spins in future detections with spin precession.