Gravitational-wave observations of binary black holes: Effect of nonquadrupole modes

We study the effect of nonquadrupolar modes in the detection and parameter estimation of gravitational waves (GWs) from nonspinning black-hole binaries. We evaluate the loss of signal-to-noise ratio and the systematic errors in the estimated parameters when one uses a quadrupole-mode template family to detect GW signals with all the relevant modes, for target signals with total masses $20{M}_{\ensuremath{\bigodot}}\ensuremath{\le}M\ensuremath{\le}250{M}_{\ensuremath{\bigodot}}$ and mass ratios $1\ensuremath{\le}q\ensuremath{\le}18$. Target signals are constructed by matching numerical-relativity simulations describing the late inspiral, merger, and ringdown of the binary with post-Newtonian/effective-one-body waveforms describing the early inspiral. We find that waveform templates modeling only the quadrupolar modes of the GW signal are sufficient (loss of detection rate $<10%$) for the detection of GWs with mass ratios $q\ensuremath{\le}4$ using advanced GW observatories. Neglecting the effect of nonquadrupole modes will introduce systematic errors in the estimated parameters. The systematic errors are larger than the expected $1\ensuremath{\sigma}$ statistical errors for binaries with large, unequal masses ($q\ensuremath{\gtrsim}4,M\ensuremath{\gtrsim}150{M}_{\ensuremath{\bigodot}}$), for sky-averaged signal-to-noise ratios larger than 8. We provide a summary of the regions in the parameter space where neglecting nonquadrupole modes will cause unacceptable loss of detection rates and unacceptably large systematic biases in the estimated parameters.