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 Autonoma de Mexico

University of Toulouse

M. Janßen

Radboud University

M. Kino

National Astronomical Observatory of Japan

M. Kramer

Max Planck Society

L. Loinard

Universidad Nacional Autonoma de Mexico

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 30

Subject Categories

Astronomy, Astrophysics and Cosmology

DOI

10.3847/1538-4357/aaf732

More information

Latest update

4/1/2021 1