Inspiral-Merger informed Ringdown analysis of black-hole merger remnants

In binary black hole mergers, the ringdown stage is characterised by quasi-normal modes with complex frequencies determined by the black hole’s mass and spin. However, the phases and amplitudes of these modes depend on the merging binary's intrinsic properties, a poorly understood relationship. Traditional analyses use a semi-agnostic approach to test the no-hair theorem, often without prior knowledge of the source. This can lead to uncertainties and an increasing number of free parameters. This paper introduces a method for quasi-normal mode analysis using the post-inspiral portion of inspiral-merger-ringdown waveform models. This approach naturally incorporates non-linearities and overtones without increasing the number of free parameters. It also imposes physically motivated priors on the amplitude and phase based on the remnant's known binary black hole origin. It also eliminates concerns over when the linear regime of the ringdown begins. I will discuss the application of this method to test the no-hair theorem with observed gravitational-wave events and comment on their higher-order mode contents.