The Astrophysical Journal Letters (Jan 2023)
The NANOGrav 15 yr Data Set: Search for Anisotropy in the Gravitational-wave Background
- Gabriella Agazie,
- Akash Anumarlapudi,
- Anne M. Archibald,
- Zaven Arzoumanian,
- Paul T. Baker,
- Bence Bécsy,
- Laura Blecha,
- Adam Brazier,
- Paul R. Brook,
- Sarah Burke-Spolaor,
- J. Andrew Casey-Clyde,
- Maria Charisi,
- Shami Chatterjee,
- Tyler Cohen,
- James M. Cordes,
- Neil J. Cornish,
- Fronefield Crawford,
- H. Thankful Cromartie,
- Kathryn Crowter,
- Megan E. DeCesar,
- Paul B. Demorest,
- Timothy Dolch,
- Brendan Drachler,
- Elizabeth C. Ferrara,
- William Fiore,
- Emmanuel Fonseca,
- Gabriel E. Freedman,
- Emiko Gardiner,
- Nate Garver-Daniels,
- Peter A. Gentile,
- Joseph Glaser,
- Deborah C. Good,
- Kayhan Gültekin,
- Jeffrey S. Hazboun,
- Ross J. Jennings,
- Aaron D. Johnson,
- Megan L. Jones,
- Andrew R. Kaiser,
- David L. Kaplan,
- Luke Zoltan Kelley,
- Matthew Kerr,
- Joey S. Key,
- Nima Laal,
- Michael T. Lam,
- William G. Lamb,
- T. Joseph W. Lazio,
- Natalia Lewandowska,
- Tingting Liu,
- Duncan R. Lorimer,
- Jing Luo,
- Ryan S. Lynch,
- Chung-Pei Ma,
- Dustin R. Madison,
- Alexander McEwen,
- James W. McKee,
- Maura A. McLaughlin,
- Natasha McMann,
- Bradley W. Meyers,
- Chiara M. F. Mingarelli,
- Andrea Mitridate,
- Cherry Ng,
- David J. Nice,
- Stella Koch Ocker,
- Ken D. Olum,
- Timothy T. Pennucci,
- Benetge B. P. Perera,
- Nihan S. Pol,
- Henri A. Radovan,
- Scott M. Ransom,
- Paul S. Ray,
- Joseph D. Romano,
- Shashwat C. Sardesai,
- Ann Schmiedekamp,
- Carl Schmiedekamp,
- Kai Schmitz,
- Levi Schult,
- Brent J. Shapiro-Albert,
- Xavier Siemens,
- Joseph Simon,
- Magdalena S. Siwek,
- Ingrid H. Stairs,
- Daniel R. Stinebring,
- Kevin Stovall,
- Abhimanyu Susobhanan,
- Joseph K. Swiggum,
- Stephen R. Taylor,
- Jacob E. Turner,
- Caner Unal,
- Michele Vallisneri,
- Sarah J. Vigeland,
- Haley M. Wahl,
- Caitlin A. Witt,
- Olivia Young
Affiliations
- Gabriella Agazie
- ORCiD
- Center for Gravitation, Cosmology and Astrophysics, Department of Physics, University of Wisconsin–Milwaukee , P.O. Box 413, Milwaukee, WI 53201, USA
- Akash Anumarlapudi
- ORCiD
- Center for Gravitation, Cosmology and Astrophysics, Department of Physics, University of Wisconsin–Milwaukee , P.O. Box 413, Milwaukee, WI 53201, USA
- Anne M. Archibald
- ORCiD
- Newcastle University , Newcastle upon Tyne NE1 7RU, UK
- Zaven Arzoumanian
- X-Ray Astrophysics Laboratory, NASA Goddard Space Flight Center , Code 662, Greenbelt, MD 20771, USA
- Paul T. Baker
- ORCiD
- Department of Physics and Astronomy, Widener University , One University Place, Chester, PA 19013, USA
- Bence Bécsy
- ORCiD
- Department of Physics, Oregon State University , Corvallis, OR 97331, USA
- Laura Blecha
- ORCiD
- Physics Department, University of Florida , Gainesville, FL 32611, USA
- Adam Brazier
- ORCiD
- Cornell Center for Astrophysics and Planetary Science and Department of Astronomy, Cornell University , Ithaca, NY 14853, USA; Cornell Center for Advanced Computing, Cornell University , Ithaca, NY 14853, USA
- Paul R. Brook
- ORCiD
- Institute for Gravitational Wave Astronomy and School of Physics and Astronomy, University of Birmingham , Edgbaston, Birmingham B15 2TT, UK
- Sarah Burke-Spolaor
- ORCiD
- Department of Physics and Astronomy, West Virginia University , P.O. Box 6315, Morgantown, WV 26506, USA; Center for Gravitational Waves and Cosmology, West Virginia University , Chestnut Ridge Research Building, Morgantown, WV 26505, USA
- J. Andrew Casey-Clyde
- ORCiD
- Department of Physics, University of Connecticut , 196 Auditorium Road, U-3046, Storrs, CT 06269-3046, USA
- Maria Charisi
- ORCiD
- Department of Physics and Astronomy, Vanderbilt University , 2301 Vanderbilt Place, Nashville, TN 37235, USA
- Shami Chatterjee
- ORCiD
- Cornell Center for Astrophysics and Planetary Science and Department of Astronomy, Cornell University , Ithaca, NY 14853, USA
- Tyler Cohen
- ORCiD
- Department of Physics, New Mexico Institute of Mining and Technology , 801 Leroy Place, Socorro, NM 87801, USA
- James M. Cordes
- ORCiD
- Cornell Center for Astrophysics and Planetary Science and Department of Astronomy, Cornell University , Ithaca, NY 14853, USA
- Neil J. Cornish
- ORCiD
- Department of Physics, Montana State University , Bozeman, MT 59717, USA
- Fronefield Crawford
- ORCiD
- Department of Physics and Astronomy, Franklin & Marshall College , P.O. Box 3003, Lancaster, PA 17604, USA
- H. Thankful Cromartie
- ORCiD
- Cornell Center for Astrophysics and Planetary Science and Department of Astronomy, Cornell University , Ithaca, NY 14853, USA
- Kathryn Crowter
- ORCiD
- Department of Physics and Astronomy, University of British Columbia , 6224 Agricultural Road, Vancouver, BC V6T 1Z1, Canada
- Megan E. DeCesar
- ORCiD
- George Mason University , Fairfax, VA 22030, USA
- Paul B. Demorest
- ORCiD
- National Radio Astronomy Observatory , 1003 Lopezville Road, Socorro, NM 87801, USA
- Timothy Dolch
- ORCiD
- Department of Physics, Hillsdale College , 33 E. College Street, Hillsdale, MI 49242, USA; Eureka Scientific , 2452 Delmer Street, Suite 100, Oakland, CA 94602-3017, USA
- Brendan Drachler
- School of Physics and Astronomy, Rochester Institute of Technology , Rochester, NY 14623, USA; Laboratory for Multiwavelength Astrophysics, Rochester Institute of Technology , Rochester, NY 14623, USA
- Elizabeth C. Ferrara
- ORCiD
- Department of Astronomy, University of Maryland , College Park, MD 20742, USA; Center for Research and Exploration in Space Science and Technology , NASA/GSFC, Greenbelt, MD 20771, USA; NASA Goddard Space Flight Center , Greenbelt, MD 20771, USA
- William Fiore
- ORCiD
- Department of Physics and Astronomy, West Virginia University , P.O. Box 6315, Morgantown, WV 26506, USA; Center for Gravitational Waves and Cosmology, West Virginia University , Chestnut Ridge Research Building, Morgantown, WV 26505, USA
- Emmanuel Fonseca
- ORCiD
- Department of Physics and Astronomy, West Virginia University , P.O. Box 6315, Morgantown, WV 26506, USA; Center for Gravitational Waves and Cosmology, West Virginia University , Chestnut Ridge Research Building, Morgantown, WV 26505, USA
- Gabriel E. Freedman
- ORCiD
- Center for Gravitation, Cosmology and Astrophysics, Department of Physics, University of Wisconsin–Milwaukee , P.O. Box 413, Milwaukee, WI 53201, USA
- Emiko Gardiner
- ORCiD
- Department of Astronomy, University of California, Berkeley , 501 Campbell Hall #3411, Berkeley, CA 94720, USA
- Nate Garver-Daniels
- ORCiD
- Department of Physics and Astronomy, West Virginia University , P.O. Box 6315, Morgantown, WV 26506, USA; Center for Gravitational Waves and Cosmology, West Virginia University , Chestnut Ridge Research Building, Morgantown, WV 26505, USA
- Peter A. Gentile
- ORCiD
- Department of Physics and Astronomy, West Virginia University , P.O. Box 6315, Morgantown, WV 26506, USA; Center for Gravitational Waves and Cosmology, West Virginia University , Chestnut Ridge Research Building, Morgantown, WV 26505, USA
- Joseph Glaser
- ORCiD
- Department of Physics and Astronomy, West Virginia University , P.O. Box 6315, Morgantown, WV 26506, USA; Center for Gravitational Waves and Cosmology, West Virginia University , Chestnut Ridge Research Building, Morgantown, WV 26505, USA
- Deborah C. Good
- ORCiD
- Department of Physics, University of Connecticut , 196 Auditorium Road, U-3046, Storrs, CT 06269-3046, USA; Center for Computational Astrophysics, Flatiron Institute , 162 5th Avenue, New York, NY 10010, USA
- Kayhan Gültekin
- ORCiD
- Department of Astronomy and Astrophysics, University of Michigan , Ann Arbor, MI 48109, USA
- Jeffrey S. Hazboun
- ORCiD
- Department of Physics, Oregon State University , Corvallis, OR 97331, USA
- Ross J. Jennings
- ORCiD
- Department of Physics and Astronomy, West Virginia University , P.O. Box 6315, Morgantown, WV 26506, USA; Center for Gravitational Waves and Cosmology, West Virginia University , Chestnut Ridge Research Building, Morgantown, WV 26505, USA
- Aaron D. Johnson
- ORCiD
- Center for Gravitation, Cosmology and Astrophysics, Department of Physics, University of Wisconsin–Milwaukee , P.O. Box 413, Milwaukee, WI 53201, USA; Division of Physics, Mathematics, and Astronomy, California Institute of Technology , Pasadena, CA 91125, USA
- Megan L. Jones
- ORCiD
- Center for Gravitation, Cosmology and Astrophysics, Department of Physics, University of Wisconsin–Milwaukee , P.O. Box 413, Milwaukee, WI 53201, USA
- Andrew R. Kaiser
- ORCiD
- Department of Physics and Astronomy, West Virginia University , P.O. Box 6315, Morgantown, WV 26506, USA; Center for Gravitational Waves and Cosmology, West Virginia University , Chestnut Ridge Research Building, Morgantown, WV 26505, USA
- David L. Kaplan
- ORCiD
- Center for Gravitation, Cosmology and Astrophysics, Department of Physics, University of Wisconsin–Milwaukee , P.O. Box 413, Milwaukee, WI 53201, USA
- Luke Zoltan Kelley
- ORCiD
- Department of Astronomy, University of California, Berkeley , 501 Campbell Hall #3411, Berkeley, CA 94720, USA
- Matthew Kerr
- ORCiD
- Space Science Division, Naval Research Laboratory , Washington, DC 20375-5352, USA
- Joey S. Key
- ORCiD
- University of Washington Bothell , 18115 Campus Way NE, Bothell, WA 98011, USA
- Nima Laal
- ORCiD
- Department of Physics, Oregon State University , Corvallis, OR 97331, USA
- Michael T. Lam
- ORCiD
- School of Physics and Astronomy, Rochester Institute of Technology , Rochester, NY 14623, USA; Laboratory for Multiwavelength Astrophysics, Rochester Institute of Technology , Rochester, NY 14623, USA
- William G. Lamb
- ORCiD
- Department of Physics and Astronomy, Vanderbilt University , 2301 Vanderbilt Place, Nashville, TN 37235, USA
- T. Joseph W. Lazio
- Jet Propulsion Laboratory, California Institute of Technology , 4800 Oak Grove Drive, Pasadena, CA 91109, USA
- Natalia Lewandowska
- ORCiD
- Department of Physics, State University of New York at Oswego , Oswego, NY 13126, USA
- Tingting Liu
- ORCiD
- Department of Physics and Astronomy, West Virginia University , P.O. Box 6315, Morgantown, WV 26506, USA; Center for Gravitational Waves and Cosmology, West Virginia University , Chestnut Ridge Research Building, Morgantown, WV 26505, USA
- Duncan R. Lorimer
- ORCiD
- Department of Physics and Astronomy, West Virginia University , P.O. Box 6315, Morgantown, WV 26506, USA; Center for Gravitational Waves and Cosmology, West Virginia University , Chestnut Ridge Research Building, Morgantown, WV 26505, USA
- Jing Luo
- ORCiD
- Department of Astronomy & Astrophysics, University of Toronto , 50 Saint George Street, Toronto, ON M5S 3H4, Canada
- Ryan S. Lynch
- ORCiD
- Green Bank Observatory , P.O. Box 2, Green Bank, WV 24944, USA
- Chung-Pei Ma
- ORCiD
- Department of Astronomy, University of California, Berkeley , 501 Campbell Hall #3411, Berkeley, CA 94720, USA; Department of Physics, University of California , Berkeley, CA 94720, USA
- Dustin R. Madison
- ORCiD
- Department of Physics, University of the Pacific , 3601 Pacific Avenue, Stockton, CA 95211, USA
- Alexander McEwen
- ORCiD
- Center for Gravitation, Cosmology and Astrophysics, Department of Physics, University of Wisconsin–Milwaukee , P.O. Box 413, Milwaukee, WI 53201, USA
- James W. McKee
- ORCiD
- E.A. Milne Centre for Astrophysics, University of Hull , Cottingham Road, Kingston-upon-Hull HU6 7RX, UK; Centre of Excellence for Data Science, Artificial Intelligence and Modelling (DAIM), University of Hull , Cottingham Road, Kingston-upon-Hull HU6 7RX, UK
- Maura A. McLaughlin
- ORCiD
- Department of Physics and Astronomy, West Virginia University , P.O. Box 6315, Morgantown, WV 26506, USA; Center for Gravitational Waves and Cosmology, West Virginia University , Chestnut Ridge Research Building, Morgantown, WV 26505, USA
- Natasha McMann
- ORCiD
- Department of Physics and Astronomy, Vanderbilt University , 2301 Vanderbilt Place, Nashville, TN 37235, USA
- Bradley W. Meyers
- ORCiD
- Department of Physics and Astronomy, University of British Columbia , 6224 Agricultural Road, Vancouver, BC V6T 1Z1, Canada; International Centre for Radio Astronomy Research, Curtin University , Bentley, WA 6102, Australia
- Chiara M. F. Mingarelli
- ORCiD
- Department of Physics, University of Connecticut , 196 Auditorium Road, U-3046, Storrs, CT 06269-3046, USA; Center for Computational Astrophysics, Flatiron Institute , 162 5th Avenue, New York, NY 10010, USA; Department of Physics, Yale University , New Haven, CT 06520, USA
- Andrea Mitridate
- ORCiD
- Deutsches Elektronen-Synchrotron DESY , Notkestr. 85, D-22607 Hamburg, Germany
- Cherry Ng
- ORCiD
- Dunlap Institute for Astronomy and Astrophysics, University of Toronto , 50 St. George Street, Toronto, ON M5S 3H4, Canada
- David J. Nice
- ORCiD
- Department of Physics, Lafayette College , Easton, PA 18042, USA
- Stella Koch Ocker
- ORCiD
- Cornell Center for Astrophysics and Planetary Science and Department of Astronomy, Cornell University , Ithaca, NY 14853, USA
- Ken D. Olum
- ORCiD
- Institute of Cosmology, Department of Physics and Astronomy, Tufts University , Medford, MA 02155, USA
- Timothy T. Pennucci
- ORCiD
- Institute of Physics and Astronomy, Eötvös Loránd University , Pázmány P.s. 1/A, 1117 Budapest, Hungary
- Benetge B. P. Perera
- ORCiD
- Arecibo Observatory , HC3 Box 53995, Arecibo, PR 00612, USA
- Nihan S. Pol
- ORCiD
- Department of Physics and Astronomy, Vanderbilt University , 2301 Vanderbilt Place, Nashville, TN 37235, USA
- Henri A. Radovan
- ORCiD
- Department of Physics, University of Puerto Rico , Mayagüez, PR 00681, USA
- Scott M. Ransom
- ORCiD
- National Radio Astronomy Observatory , 520 Edgemont Road, Charlottesville, VA 22903, USA
- Paul S. Ray
- ORCiD
- Space Science Division, Naval Research Laboratory , Washington, DC 20375-5352, USA
- Joseph D. Romano
- ORCiD
- Department of Physics, Texas Tech University , Box 41051, Lubbock, TX 79409, USA
- Shashwat C. Sardesai
- ORCiD
- Center for Gravitation, Cosmology and Astrophysics, Department of Physics, University of Wisconsin–Milwaukee , P.O. Box 413, Milwaukee, WI 53201, USA
- Ann Schmiedekamp
- ORCiD
- Department of Physics, Penn State Abington , Abington, PA 19001, USA
- Carl Schmiedekamp
- ORCiD
- Department of Physics, Penn State Abington , Abington, PA 19001, USA
- Kai Schmitz
- ORCiD
- Institute for Theoretical Physics, University of Münster , D-48149 Münster, Germany
- Levi Schult
- ORCiD
- Department of Physics and Astronomy, Vanderbilt University , 2301 Vanderbilt Place, Nashville, TN 37235, USA
- Brent J. Shapiro-Albert
- ORCiD
- Department of Physics and Astronomy, West Virginia University , P.O. Box 6315, Morgantown, WV 26506, USA; Center for Gravitational Waves and Cosmology, West Virginia University , Chestnut Ridge Research Building, Morgantown, WV 26505, USA; Giant Army , 915A 17th Avenue, Seattle WA 98122, USA
- Xavier Siemens
- ORCiD
- Center for Gravitation, Cosmology and Astrophysics, Department of Physics, University of Wisconsin–Milwaukee , P.O. Box 413, Milwaukee, WI 53201, USA; Department of Physics, Oregon State University , Corvallis, OR 97331, USA
- Joseph Simon
- ORCiD
- Department of Astrophysical and Planetary Sciences, University of Colorado , Boulder, CO 80309, USA
- Magdalena S. Siwek
- ORCiD
- Center for Astrophysics, Harvard University , 60 Garden Street, Cambridge, MA 02138, USA
- Ingrid H. Stairs
- ORCiD
- Department of Physics and Astronomy, University of British Columbia , 6224 Agricultural Road, Vancouver, BC V6T 1Z1, Canada
- Daniel R. Stinebring
- ORCiD
- Department of Physics and Astronomy, Oberlin College , Oberlin, OH 44074, USA
- Kevin Stovall
- ORCiD
- National Radio Astronomy Observatory , 1003 Lopezville Road, Socorro, NM 87801, USA
- Abhimanyu Susobhanan
- ORCiD
- Center for Gravitation, Cosmology and Astrophysics, Department of Physics, University of Wisconsin–Milwaukee , P.O. Box 413, Milwaukee, WI 53201, USA
- Joseph K. Swiggum
- ORCiD
- Department of Physics, Lafayette College , Easton, PA 18042, USA
- Stephen R. Taylor
- ORCiD
- Department of Physics and Astronomy, Vanderbilt University , 2301 Vanderbilt Place, Nashville, TN 37235, USA
- Jacob E. Turner
- ORCiD
- Department of Physics and Astronomy, West Virginia University , P.O. Box 6315, Morgantown, WV 26506, USA; Center for Gravitational Waves and Cosmology, West Virginia University , Chestnut Ridge Research Building, Morgantown, WV 26505, USA
- Caner Unal
- ORCiD
- Department of Physics, Ben-Gurion University of the Negev , Be’er Sheva 84105, Israel; Feza Gursey Institute, Bogazici University , Kandilli, 34684, Istanbul, Turkey
- Michele Vallisneri
- ORCiD
- Division of Physics, Mathematics, and Astronomy, California Institute of Technology , Pasadena, CA 91125, USA; Jet Propulsion Laboratory, California Institute of Technology , 4800 Oak Grove Drive, Pasadena, CA 91109, USA
- Sarah J. Vigeland
- ORCiD
- Center for Gravitation, Cosmology and Astrophysics, Department of Physics, University of Wisconsin–Milwaukee , P.O. Box 413, Milwaukee, WI 53201, USA
- Haley M. Wahl
- ORCiD
- Department of Physics and Astronomy, West Virginia University , P.O. Box 6315, Morgantown, WV 26506, USA; Center for Gravitational Waves and Cosmology, West Virginia University , Chestnut Ridge Research Building, Morgantown, WV 26505, USA
- Caitlin A. Witt
- ORCiD
- Center for Interdisciplinary Exploration and Research in Astrophysics (CIERA), Northwestern University , Evanston, IL 60208, USA; Adler Planetarium , 1300 S. DuSable Lake Shore Drive, Chicago, IL 60605, USA
- Olivia Young
- ORCiD
- School of Physics and Astronomy, Rochester Institute of Technology , Rochester, NY 14623, USA; Laboratory for Multiwavelength Astrophysics, Rochester Institute of Technology , Rochester, NY 14623, USA
- DOI
- https://doi.org/10.3847/2041-8213/acf4fd
- Journal volume & issue
-
Vol. 956,
no. 1
p. L3
Abstract
The North American Nanohertz Observatory for Gravitational Waves (NANOGrav) has reported evidence for the presence of an isotropic nanohertz gravitational-wave background (GWB) in its 15 yr data set. However, if the GWB is produced by a population of inspiraling supermassive black hole binary (SMBHB) systems, then the background is predicted to be anisotropic, depending on the distribution of these systems in the local Universe and the statistical properties of the SMBHB population. In this work, we search for anisotropy in the GWB using multiple methods and bases to describe the distribution of the GWB power on the sky. We do not find significant evidence of anisotropy. By modeling the angular power distribution as a sum over spherical harmonics (where the coefficients are not bound to always generate positive power everywhere), we find that the Bayesian 95% upper limit on the level of dipole anisotropy is ( C _l _=1 / C _l _=0 ) < 27%. This is similar to the upper limit derived under the constraint of positive power everywhere, indicating that the dipole may be close to the data-informed regime. By contrast, the constraints on anisotropy at higher spherical-harmonic multipoles are strongly prior dominated. We also derive conservative estimates on the anisotropy expected from a random distribution of SMBHB systems using astrophysical simulations conditioned on the isotropic GWB inferred in the 15 yr data set and show that this data set has sufficient sensitivity to probe a large fraction of the predicted level of anisotropy. We end by highlighting the opportunities and challenges in searching for anisotropy in pulsar timing array data.
Keywords
