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

accretion, accretion disks

techniques: interferometric

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

Radboud University

Leiden University

Ivan Marti-Vidal

Chalmers, Space, Earth and Environment, Onsala Space Observatory

Jan Wagner

Max Planck Institute

S. Doeleman

Harvard-Smithsonian Center for Astrophysics

H.D. Falcke

Radboud University

T.P. Krichbaum

Max Planck Institute

Kazunori Akiyama

National Radio Astronomy Observatory

Massachusetts Institute of Technology (MIT)

U. Bach

Max Planck Institute

K. L. Bouman

Harvard-Smithsonian Center for Astrophysics

G. C. Bower

Academia Sinica

Avery E. Broderick

Perimeter Institute for Theoretical Physics

I. Cho

University of Science and Technology (UST)

Korea Astronomy and Space Science Institute

G. Crew

Massachusetts Institute of Technology (MIT)

Jason Dexter

Max Planck Institute

V. Fish

Massachusetts Institute of Technology (MIT)

R. Gold

Perimeter Institute for Theoretical Physics

Goethe University Frankfurt

J. L. Gomez

CSIC - Instituto de Astrofísica de Andalucía (IAA)

K. Hada

National Institutes of Natural Sciences - National Astronomical Observatory of Japan

A. Hernández-Gómez

University of Toulouse

Universidad Nacional Autonoma de Mexico

M. Janßen

Radboud University

M. Kino

National Institutes of Natural Sciences - National Astronomical Observatory of Japan

M. Kramer

Max Planck Institute

L. Loinard

Universidad Nacional Autonoma de Mexico

R.S. Lu

Shanghai Astronomical Observatory

Max Planck Institute

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 Institute

F. Roelofs

Radboud University

Eduardo Ros

Max Planck Institute

H. Rottmann

Max Planck Institute

S. Sanchez

Instituto de Radioastronomía Milimétrica

R. P. J. Tilanus

Radboud University

Leiden University

P. Vicente

Observatorio de Yebes (IGN)

M. Wielgus

Harvard-Smithsonian Center for Astrophysics

A.J. Zensus

Max Planck Institute

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

3/5/2019 9