Persistent Non-Gaussian Structure in the Image of Sagittarius A at 86 GHz

• Published in: The Astrophysical journal Vol. 915; no. 2; pp. 99 - 112
• Main Authors: Issaoun, S., Johnson, M. D., Blackburn, L., Broderick, A., Tiede, P., Wielgus, M., Doeleman, S. S., Falcke, H., Akiyama, K., Bower, G. C., Brinkerink, C. D., Chael, A., Cho, I., Gómez, J. L., Hernández-Gómez, A., Hughes, D., Kino, M., Krichbaum, T. P., Liuzzo, E., Loinard, L., Markoff, S., Marrone, D. P., Mizuno, Y., Moran, J. M., Pidopryhora, Y., Ros, E., Rygl, K., Shen, Z.-Q., Wagner, J.
• Format: Journal Article
• Language: English
• Published: Philadelphia The American Astronomical Society 01-07-2021; IOP Publishing
• Subjects: Arrays; Astrophysics; Black holes; Constraint modelling; Flux density; Galactic center; Interferometry; Interstellar; Interstellar medium; Interstellar turbulence; Morphology; Radio interferometry; Radio telescopes; Scattering; Supermassive black holes; Very long base interferometry; Very long baseline interferometry; Wavelengths
• ISSN: 0004-637X; 1538-4357
• DOI: 10.3847/1538-4357/ac00b0

Abstract
Observations of the Galactic Center supermassive black hole Sagittarius A* (Sgr A*) with very long-baseline interferometry (VLBI) are affected by interstellar scattering along our line of sight. At long radio observing wavelengths (≲1 cm), the scattering heavily dominates image morphology. At 3.5 mm (86 GHz), the intrinsic source structure is no longer sub-dominant to scattering, and thus the intrinsic emission from Sgr A* is resolvable with the Global Millimeter VLBI Array (GMVA). Long-baseline detections to the phased Atacama Large Millimeter/submillimeter Array (ALMA) in 2017 provided new constraints on the intrinsic and scattering properties of Sgr A*, but the stochastic nature of the scattering Requires multiple observing epochs to reliably estimate its statistical properties. We present new observations with the GMVA+ALMA, taken in 2018, which confirm non-Gaussian structure in the scattered image seen in 2017. In particular, the ALMA–GBT baseline shows more flux density than expected for an anistropic Gaussian model, providing a tight constraint on the source size and an upper limit on the dissipation scale of interstellar turbulence. We find an intrinsic source extent along the minor axis of ∼100
μ
as both via extrapolation of longer wavelength scattering constraints and direct modeling of the 3.5 mm observations. Simultaneously fitting for the scattering parameters, we find an at-most modestly asymmetrical (major-to-minor axis ratio of 1.5 ± 0.2) intrinsic source morphology for Sgr A*.