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(circle dot) <= M <= 250M(circle dot) 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 GWobservatories. Neglecting the effect of nonquadrupole modes will introduce systematic errors in the estimated parameters. The systematic errors are larger than the expected 1 sigma statistical errors for binaries with large, unequal masses (q greater than or similar to 4, M greater than or similar to 150M(circle dot)), 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.