The NANOGrav 15-year Data Set: Constraints on Supermassive Black Hole Binaries from the Gravitational Wave Background
Creators: name: Agazie, Gabriella
name: Anumarlapudi, Akash
name: Archibald, Anne M.
name: Baker, Paul T.
name: Bécsy, Bence
name: Blecha, Laura
name: Bonilla, Alexander
name: Brazier, Adam
name: Brook, Paul R.
name: Burke-Spolaor, Sarah
name: Burnette, Rand
name: Case, Robin
name: Casey-Clyde, J. Andrew
name: Charisi, Maria
name: Chatterjee, Shami
name: Chatziioannou, Katerina
name: Cheeseboro, Belinda D.
name: Chen, Siyuan
name: Cohen, Tyler
name: Cordes, James M.
name: Cornish, Neil J.
name: Crawford, Fronefield
name: Cromartie, H. Thankful
name: Crowter, Kathryn
name: Cutler, Curt J.
name: D'Orazio, Daniel J.
name: DeCesar, Megan E.
name: DeGan, Dallas
name: Demorest, Paul B.
name: Deng, Heling
name: Dolch, Timothy
name: Drachler, Brendan
name: Ferrara, Elizabeth C.
name: Fiore, William
name: Fonseca, Emmanuel
name: Freedman, Gabriel E.
name: Gardiner, Emiko
name: Garver-Daniels, Nate
name: Gentile, Peter A.
name: Gersbach, Kyle A.
name: Glaser, Joseph
name: Good, Deborah C.
name: Gültekin, Kayhan
name: Hazboun, Jeffrey S.
name: Hourihane, Sophie
name: Islo, Kristina
name: Jennings, Ross J.
name: Johnson, Aaron
name: Jones, Megan L.
name: Kaiser, Andrew R.
name: Kaplan, David L.
name: Kelley, Luke Zoltan
name: Kerr, Matthew
name: Key, Joey S.
name: Laal, Nima
name: Lam, Michael T.
name: Lamb, William G.
name: Lazio, T. Joseph W.
name: Lewandowska, Natalia
name: Littenberg, Tyson B.
name: Liu, Tingting
name: Luo, Jing
name: Lynch, Ryan S.
name: Ma, Chung-Pei
name: Madison, Dustin R.
name: McEwen, Alexander
name: McKee, James W.
name: McLaughlin, Maura A.
name: McMann, Natasha
name: Meyers, Bradley W.
name: Meyers, Patrick M.
name: Mingarelli, Chiara M. F.
name: Mitridate, Andrea
name: Natarajan, Priyamvada
name: Ng, Cherry
name: Nice, David J.
name: Ocker, Stella Koch
name: Olum, Ken D.
name: Pennucci, Timothy T.
name: Perera, Benetge B. P.
name: Petrov, Polina
name: Pol, Nihan S.
name: Radovan, Henri A.
name: Ransom, Scott M.
name: Ray, Paul S.
name: Romano, Joseph D.
name: Runnoe, Jessie C.
name: Sardesai, Shashwat C.
name: Schmiedekamp, Ann
name: Schmiedekamp, Carl
name: Schmitz, Kai
name: Schult, Levi
name: Shapiro-Albert, Brent J.
name: Siemens, Xavier
name: Simon, Joseph
name: Siwek, Magdalena S.
name: Stairs, Ingrid H.
name: Stinebring, Daniel R.
name: Stovall, Kevin
name: Sun, Jerry P.
name: Susobhanan, Abhimanyu
name: Swiggum, Joseph K.
name: Taylor, Jacob
name: Taylor, Stephen R.
name: Turner, Jacob E.
name: Unal, Caner
name: Vallisneri, Michele
name: Vigeland, Sarah J.
name: Wachter, Jeremy M.
name: Wahl, Haley M.
name: Wang, Qiaohong
name: Witt, Caitlin A.
name: Wright, David
name: Young, Olivia
Publisher: name: arXiv
Year: 2023
Subjects: subject: High Energy Astrophysical Phenomena (astro-ph.HE)
subject: Cosmology and Nongalactic Astrophysics (astro-ph.CO)
subject: General Relativity and Quantum Cosmology (gr-qc)
subject: FOS: Physical sciences
subject: FOS: Physical sciences

description: The NANOGrav 15-year data set shows evidence for the presence of a low-frequency gravitational-wave background (GWB). While many physical processes can source such low-frequency gravitational waves, here we analyze the signal as coming from a population of supermassive black hole (SMBH) binaries distributed throughout the Universe. We show that astrophysically motivated models of SMBH binary populations are able to reproduce both the amplitude and shape of the observed low-frequency gravitational-wave spectrum. While multiple model variations are able to reproduce the GWB spectrum at our current measurement precision, our results highlight the importance of accurately modeling binary evolution for producing realistic GWB spectra. Additionally, while reasonable parameters are able to reproduce the 15-year observations, the implied GWB amplitude necessitates either a large number of parameters to be at the edges of expected values, or a small number of parameters to be notably different from standard expectations. While we are not yet able to definitively establish the origin of the inferred GWB signal, the consistency of the signal with astrophysical expectations offers a tantalizing prospect for confirming that SMBH binaries are able to form, reach sub-parsec separations, and eventually coalesce. As the significance grows over time, higher-order features of the GWB spectrum will definitively determine the nature of the GWB and allow for novel constraints on SMBH populations.
description: Accepted by Astrophysical Journal Letters as part of Focus on NANOGrav's 15-year Data Set and the Gravitational Wave Background. For questions or comments, please email comments@nanograv.org. Edited to fix two equation typos (Eq.13 &amp; 21), and minor text typos