The Size, Shape, and Scattering of Sagittarius A∗ at 86 GHz: First VLBI with ALMA
Journal article, 2019
The Galactic center supermassive black hole Sagittarius A∗ (Sgr A∗) is one of the most promising targets to study the dynamics of black hole accretion and outflow via direct imaging with very long baseline interferometry (VLBI). At 3.5 mm (86 GHz), the emission from Sgr A∗ is resolvable with the Global Millimeter VLBI Array (GMVA). We present the first observations of Sgr A∗ with the phased Atacama Large Millimeter/submillimeter Array (ALMA) joining the GMVA. Our observations achieve an angular resolution of ∼87 μas, improving upon previous experiments by a factor of two. We reconstruct a first image of the unscattered source structure of Sgr A∗ at 3.5 mm, mitigating the effects of interstellar scattering. The unscattered source has a major-axis size of 120 ±34 μas (12 ±3.4 Schwarzschild radii) and a symmetrical morphology (axial ratio of ), which is further supported by closure phases consistent with zero within 3σ. We show that multiple disk-dominated models of Sgr A∗ match our observational constraints, while the two jet-dominated models considered are constrained to small viewing angles. Our long-baseline detections to ALMA also provide new constraints on the scattering of Sgr A∗, and we show that refractive scattering effects are likely to be weak for images of Sgr A∗ at 1.3 mm with the Event Horizon Telescope. Our results provide the most stringent constraints to date for the intrinsic morphology and refractive scattering of Sgr A∗, demonstrating the exceptional contribution of ALMA to millimeter VLBI.
galaxies: individual (Sgr A∗)
Galaxy: center
techniques: interferometric
accretion, accretion disks
Author
S. Issaoun
Harvard-Smithsonian Center for Astrophysics
Radboud University
Michael D. Johnson
Harvard-Smithsonian Center for Astrophysics
Lindy Blackburn
Harvard-Smithsonian Center for Astrophysics
C. D. Brinkerink
Radboud University
M. Mościbrodzka
Radboud University
A. Chael
Harvard-Smithsonian Center for Astrophysics
C. Goddi
Leiden University
Radboud University
Ivan Marti-Vidal
Chalmers, Space, Earth and Environment, Onsala Space Observatory
Jan Wagner
Max Planck Society
S. Doeleman
Harvard-Smithsonian Center for Astrophysics
H.D. Falcke
Radboud University
T.P. Krichbaum
Max Planck Society
Kazunori Akiyama
Massachusetts Institute of Technology (MIT)
National Radio Astronomy Observatory
U. Bach
Max Planck Society
K. L. Bouman
Harvard-Smithsonian Center for Astrophysics
G. C. Bower
Academia Sinica
Avery E. Broderick
Perimeter Institute for Theoretical Physics
I. Cho
Korea Astronomy and Space Science Institute
University of Science and Technology (UST)
G. Crew
Massachusetts Institute of Technology (MIT)
Jason Dexter
Max Planck Society
V. Fish
Massachusetts Institute of Technology (MIT)
R. Gold
Perimeter Institute for Theoretical Physics
Goethe University Frankfurt
J. L. Gomez
Institute of Astrophysics of Andalusia (IAA)
K. Hada
National Astronomical Observatory of Japan
A. Hernández-Gómez
Universidad Nacional Autónoma de México
University of Toulouse
M. Janßen
Radboud University
M. Kino
National Astronomical Observatory of Japan
M. Kramer
Max Planck Society
L. Loinard
Universidad Nacional Autónoma de México
R.S. Lu
Shanghai Astronomical Observatory
Max Planck Society
S. Markoff
University of Amsterdam
D. P. Marrone
University of Arizona
L. D. Matthews
Massachusetts Institute of Technology (MIT)
J. M. Moran
Harvard-Smithsonian Center for Astrophysics
C. Müller
Radboud University
Max Planck Society
F. Roelofs
Radboud University
Eduardo Ros
Max Planck Society
H. Rottmann
Max Planck Society
S. Sanchez
Institut de Radioastronomie Millimétrique (IRAM)
R. P. J. Tilanus
Leiden University
Radboud University
P. Vicente
Yebes Observatory
M. Wielgus
Harvard-Smithsonian Center for Astrophysics
A.J. Zensus
Max Planck Society
G. Y. Zhao
Korea Astronomy and Space Science Institute
Astrophysical Journal
0004-637X (ISSN) 1538-4357 (eISSN)
Vol. 871 1 30Subject Categories
Astronomy, Astrophysics and Cosmology
DOI
10.3847/1538-4357/aaf732