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Lookup NU author(s): Dr Anne ArchibaldORCiD
This work is licensed under a Creative Commons Attribution 4.0 International License (CC BY 4.0).
© 2026. The Author(s). Published by the American Astronomical Society.We test the impact of an evolving supermassive black hole 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 (GSMF) 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 GSMF that implies an undetected population of massive galaxies (M⋆ ≥ 1011M⊙ 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 α(z) = α0(1 + z)1.04±0.5
Author(s): Matt C, Gultekin K, Kelley LZ, Blecha L, Simon J, Agazie G, Anumarlapudi A, Archibald AM, Arzoumanian Z, Baier JG, Baker PT, Becsy B, Brazier A, Brook PR, Burke-Spolaor S, Burnette R, Case R, Casey-Clyde JA, Charisi M, Chatterjee S, Cohen T, Cordes JM, Cornish NJ, Crawford F, Cromartie HT, Crowter K, DeCesar ME, Demorest PB, Deng H, Dey L, Dolch T, Ferrara EC, Fiore W, Fonseca E, Freedman GE, Gardiner EC, Garver-Daniels N, Gentile PA, Gersbach KA, Glaser J, Good DC, Harris CJ, Hazboun JS, Jennings RJ, Johnson AD, Jones ML, Kaplan DL, Kerr M, Key JS, Laal N, Lam MT, Lamb WG, Larsen B, Lazio TJW, Lewandowska N, Liu T, Lorimer DR, Luo J, Lynch RS, Ma C-P, Madison DR, McEwen A, McKee JW, McLaughlin MA, McMann N, Meyers BW, Meyers PM, Mingarelli CMF, Mitridate A, Ng C, Nice DJ, Ocker SK, Olum KD, Pennucci TT, Perera BBP, Petrov P, Pol NS, Radovan HA, Ransom SM, Ray PS, Romano JD, Runnoe JC, Saffer A, Sardesai SC, Schmiedekamp A, Schmiedekamp C, Schmitz K, Shapiro-Albert BJ, Siemens X, Fiscella SVS, Stairs IH, Stinebring DR, Stovall K, Susobhanan A, Swiggum JK, Taylor J, Taylor SR, Thompson MS, Turner JE, Vallisneri M, van Haasteren R, Vigeland SJ, Wahl HM, Wilson KP, Witt CA, Wright D, Young O
Publication type: Article
Publication status: Published
Journal: Astrophysical Journal
Year: 2026
Volume: 997
Issue: 2
Online publication date: 22/01/2026
Acceptance date: 26/11/2025
Date deposited: 15/04/2026
ISSN (print): 0004-637X
ISSN (electronic): 1538-4357
Publisher: American Astronomical Society
URL: https://doi.org/10.3847/1538-4357/ae2480
DOI: 10.3847/1538-4357/ae2480
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