Detection of (2,2) quasinormal mode from a population of black holes with a constructive summation method

The quasinormal modes associated with gravitational-wave signals from binary black hole (BBH) mergers can provide deep insight into the remnant's properties. Once design sensitivity is achieved, present ground-based gravitational-wave interferometers could detect potentially hundreds of BBH signals in the coming years. But for most, the ringdown phase will have a very weak signal-to-noise ratio (SNR), and therefore poor, if any, scientific information could be extracted from them. We review how a summation method can help detect these weak (2,2) QNMs and potentially allow us to use their information. The method is based on two main steps: the signal's rescaling and synchronization. In this first study, we tested the method under limited BBH parameters and review its principal limitations. In particular, the synchronization that fails for the weakest signals requires selecting ringdowns with a SNR above 2.6. Using this threshold, we show that for two different BBH populations 40% to 70% of all the potential detections could still be used for the summation while ensuring a summed SNR of ∼80% of the maximal achievable SNR (i.e., for ideally synchronized signals).