Exploration of features in the black hole mass spectrum inspired by non-parametric analyses of gravitational wave observations

¹ Universität Heidelberg, Zentrum für Astronomie (ZAH), Institut für Theoretische Astrophysik, Albert-Ueberle-Str. 2, 69120 Heidelberg, Germany
² Dipartimento di Fisica e Astronomia “G. Galilei”, Università di Padova, Via Marzolo 8, 35122 Padova, Italy
³ Chair of Physics Education Research, Faculty of Physics, Ludwig-Maximilians-Universität München, Munich, Germany
⁴ Dipartimento di Fisica e Astronomia, Università degli Studi di Firenze, Via Sansone 1, Sesto Fiorentino, 50019, Italy
⁵ INFN, Sezione di Firenze, Via Sansone 1, Sesto Fiorentino, 50019, Italy
⁶ Universität Heidelberg, Interdisziplinäres Zentrum für Wissenschaftliches Rechnen, Heidelberg, Germany
⁷ INFN, Sezione di Padova, Via Marzolo 8, I-35131 Padova, Italy
⁸ Dipartimento di Fisica “E. Fermi”, Università di Pisa, Largo Bruno Pontecorvo 3, Pisa, I-56127, Italy
⁹ INFN, Sezione di Pisa, Largo Bruno Pontecorvo 3, Pisa, I-56127, Italy

^⋆ Corresponding authors: stefano.rinaldi@uni-heidelberg.de; yajie.liang@lmu.de

Received: 9 June 2025
Accepted: 13 August 2025

Abstract

Context. Current gravitational-wave data reveal structures in the mass function of binary compact objects. Properly modelling and deciphering such structures is the ultimate goal of gravitational-wave population analysis; in this context, non-parametric models are a powerful tool to infer the distribution of black holes from gravitational waves without committing to any specific functional form.

Aims. Here we aim to quantitatively corroborate the findings of non-parametric methods with parametrised models incorporating the features found in such analyses.

Methods. We propose two modifications of the currently favoured POWERLAW+PEAK model, inspired by non-parametric studies, and use them to analyse the third Gravitational Wave Transient Catalogue.

Results. Our analysis marginally supports the existence of two distinct, differently redshift-evolving subpopulations in the black hole primary mass function, and suggests that, to date, we are still unable to robustly assess the shape of the mass ratio distribution for symmetric (q >  0.7) binaries.