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arXiv · 2508.18126

Inferring Mbh-Mbulge Evolution from the Gravitational Wave Background

Cayenne Matt·Kayhan Gultekin·Luke Kelley·Laura Blecha·Joseph Simon·Gabriella Agazie·Akash Anumarlapudi·Anne Archibald·Zaven Arzoumanian·Jeremy Baier·Paul Baker·Bence Bécsy·Adam Brazier·Paul Brook·Sarah Burke-Spolaor·Rand Burnette·Robin Case·James Casey-Clyde·Maria Charisi·Shami Chatterjee·Tyler Cohen·James Cordes·Neil Cornish·Fronefield Crawford·H. Thankful Cromartie·Kathryn Crowter·Megan DeCesar·Paul Demorest·Heling Deng·Lankeswar Dey·Timothy Dolch·Elizabeth Ferrara·William Fiore·Emmanuel Fonseca·Gabriel Freedman·Emiko Gardiner·Nate Garver-Daniels·Peter Gentile·Kyle Gersbach·Joseph Glaser·Deborah Good·C. Harris·Jeffrey Hazboun·Ross Jennings·Aaron Johnson·Megan Jones·David Kaplan·Matthew Kerr·Joey Key·Nima Laal·Michael Lam·William Lamb·Bjorn Larsen·T. Lazio·Natalia Lewandowska·Tingting Liu·Duncan Lorimer·Jing Luo·Ryan Lynch·Chung-Pei Ma·Dustin Madison·Alexander McEwen·James McKee·Maura McLaughlin·Natasha McMann·Bradley Meyers·Patrick Meyers·Chiara Mingarelli·Andrea Mitridate·Cherry Ng·David Nice·Stella Ocker·Ken Olum·Timothy Pennucci·Benetge Perera·Polina Petrov·Nihan Pol·Henri Radovan·Scott Ransom·Paul Ray·Joseph Romano·Jessie Runnoe·Alexander Saffer·Shashwat Sardesai·A. Schmiedekamp·Carl Schmiedekamp·Kai Schmitz·Brent Shapiro-Albert·Xavier Siemens·Sophia Sosa Fiscella·Ingrid Stairs·Daniel Stinebring·Kevin Stovall·Abhimanyu Susobhanan·Joseph Swiggum·Jacob Taylor·Stephen Taylor·Mercedes Thompson·Jacob Turner·Michele Vallisneri
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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).

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Cayenne Matt, Kayhan Gultekin, Luke Kelley, Laura Blecha, Joseph Simon, Gabriella Agazie, Akash Anumarlapudi, Anne Archibald, Zaven Arzoumanian, Jeremy Baier, Paul Baker, Bence Bécsy, Adam Brazier, Paul Brook, Sarah Burke-Spolaor, Rand Burnette, Robin Case, James Casey-Clyde, Maria Charisi, Shami Chatterjee, Tyler Cohen, James Cordes, Neil Cornish, Fronefield Crawford, H. Thankful Cromartie, Kathryn Crowter, Megan DeCesar, Paul Demorest, Heling Deng, Lankeswar Dey, Timothy Dolch, Elizabeth Ferrara, William Fiore, Emmanuel Fonseca, Gabriel Freedman, Emiko Gardiner, Nate Garver-Daniels, Peter Gentile, Kyle Gersbach, Joseph Glaser, Deborah Good, C. Harris, Jeffrey Hazboun, Ross Jennings, Aaron Johnson, Megan Jones, David Kaplan, Matthew Kerr, Joey Key, Nima Laal, Michael Lam, William Lamb, Bjorn Larsen, T. Lazio, Natalia Lewandowska, Tingting Liu, Duncan Lorimer, Jing Luo, Ryan Lynch, Chung-Pei Ma, Dustin Madison, Alexander McEwen, James McKee, Maura McLaughlin, Natasha McMann, Bradley Meyers, Patrick Meyers, Chiara Mingarelli, Andrea Mitridate, Cherry Ng, David Nice, Stella Ocker, Ken Olum, Timothy Pennucci, Benetge Perera, Polina Petrov, Nihan Pol, Henri Radovan, Scott Ransom, Paul Ray, Joseph Romano, Jessie Runnoe, Alexander Saffer, Shashwat Sardesai, A. Schmiedekamp, Carl Schmiedekamp, Kai Schmitz, Brent Shapiro-Albert, Xavier Siemens, Sophia Sosa Fiscella, Ingrid Stairs, Daniel Stinebring, Kevin Stovall, Abhimanyu Susobhanan, Joseph Swiggum, Jacob Taylor, Stephen Taylor, Mercedes Thompson, Jacob Turner, Michele Vallisneri. 2025-12-08. Inferring Mbh-Mbulge Evolution from the Gravitational Wave Background. https://doi.org/10.3847/1538-4357%2Fae2480

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