Inferring Mbh-Mbulge Evolution from the Gravitational Wave Background
Abstract
We test the impact of an evolving supermassive black hole (SMBH) mass scaling relation (Mbh-Mbulge) on the predictions for the gravitational wave background (GWB). The observed GWB amplitude is 2-3 times higher than predicted by astrophysically informed models which suggests the need to revise the assumptions in those models. We compare a semi-analytic model's ability to reproduce the observed GWB spectrum with a static versus evolving-amplitude Mbh-Mbulge relation. We additionally consider the influence of the choice of galaxy stellar mass function on the modeled GWB spectra. Our models are able to reproduce the GWB amplitude with either a large number density of massive galaxies or a positively evolving Mbh-Mbulge amplitude (i.e., the Mbh / Mbulge ratio was higher in the past). If we assume that the Mbh-Mbulge amplitude does not evolve, our models require a galaxy stellar mass function that implies an undetected population of massive galaxies (Mstellar > 10^11 Msun at z > 1). When the Mbh-Mbulge amplitude is allowed to evolve, we can model the GWB spectrum with all fiducial values and an Mbh-Mbulge amplitude that evolves as alpha(z) = alpha_0 (1 + z)^(1.04 +/- 0.5).
Cite
@article{arxiv.2508.18126,
title = {Inferring Mbh-Mbulge Evolution from the Gravitational Wave Background},
author = {Cayenne Matt and Kayhan Gultekin and Luke Kelley and Laura Blecha and Joseph Simon and Gabriella Agazie and Akash Anumarlapudi and Anne Archibald and Zaven Arzoumanian and Jeremy Baier and Paul Baker and Bence Bécsy and Adam Brazier and Paul Brook and Sarah Burke-Spolaor and Rand Burnette and Robin Case and James Casey-Clyde and Maria Charisi and Shami Chatterjee and Tyler Cohen and James Cordes and Neil Cornish and Fronefield Crawford and H. Thankful Cromartie and Kathryn Crowter and Megan DeCesar and Paul Demorest and Heling Deng and Lankeswar Dey and Timothy Dolch and Elizabeth Ferrara and William Fiore and Emmanuel Fonseca and Gabriel Freedman and Emiko Gardiner and Nate Garver-Daniels and Peter Gentile and Kyle Gersbach and Joseph Glaser and Deborah Good and C. Harris and Jeffrey Hazboun and Ross Jennings and Aaron Johnson and Megan Jones and David Kaplan and Matthew Kerr and Joey Key and Nima Laal and Michael Lam and William Lamb and Bjorn Larsen and T. Lazio and Natalia Lewandowska and Tingting Liu and Duncan Lorimer and Jing Luo and Ryan Lynch and Chung-Pei Ma and Dustin Madison and Alexander McEwen and James McKee and Maura McLaughlin and Natasha McMann and Bradley Meyers and Patrick Meyers and Chiara Mingarelli and Andrea Mitridate and Cherry Ng and David Nice and Stella Ocker and Ken Olum and Timothy Pennucci and Benetge Perera and Polina Petrov and Nihan Pol and Henri Radovan and Scott Ransom and Paul Ray and Joseph Romano and Jessie Runnoe and Alexander Saffer and Shashwat Sardesai and A. Schmiedekamp and Carl Schmiedekamp and Kai Schmitz and Brent Shapiro-Albert and Xavier Siemens and Sophia Sosa Fiscella and Ingrid Stairs and Daniel Stinebring and Kevin Stovall and Abhimanyu Susobhanan and Joseph Swiggum and Jacob Taylor and Stephen Taylor and Mercedes Thompson and Jacob Turner and Michele Vallisneri and Rutger van Haasteren and Sarah Vigeland and Haley Wahl and Kevin Wilson and Caitlin Witt and David Wright and Olivia Young},
journal= {arXiv preprint arXiv:2508.18126},
year = {2026}
}
Comments
Accepted for publication in ApJ