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 20M⊙≤M≤250M⊙ and mass ratios 1≤q≤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≤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 1σ statistical errors for binaries with large, unequal masses (q≳4,M≳150M⊙), 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.