Title: Evidence for subdominant multipole moments and precession in merging black-hole-binaries from GWTC-2.1
Abstract: The LIGO--Virgo--KAGRA collaborations (LVK) produced a catalog containing gravitational-wave (GW) observations from the first half of the third GW observing run (O3a). This catalog, GWTC-2.1, includes for the first time a number of exceptional GW candidates produced from merging black-hole-binaries with unequivocally unequal component masses. Since subdominant multipole moments and spin-induced orbital precession are more likely to leave measurable imprints on the emitted GW from unequal component mass binaries, these general relativistic phenomena may now be measurable. Indeed, both GW190412 and GW190814 have already shown conclusive evidence for subdominant multipole moments. This provides valuable insights into the dynamics of the binary. We calculate the evidence for subdominant multipole moments and spin-induced orbital precession for all merging black-hole-binaries in GWTC-2.1 that were observed during O3a and show that (a) no gravitational-wave candidate has measurable higher order multipole content beyond $\ensuremath{\ell}=3$, (b) in addition to the confident subdominant multipole measurements in GW190412 and GW190814, GW190519_153544 and GW190929_012149 show marginal evidence for the $(\ensuremath{\ell},|m|)=(3,3)$ subdominant multipole, (c) GW190521 shows no evidence for precession but it may have measurable subdominant multipole content and (d) GW190412 may show evidence for spin-induced orbital precession and (e) we observe no significant evidence for precession in the current population of binary black hole mergers.