@article{2243fcc74fb844dca33a5ca01fc08ee2,
title = "Hydrodynamic simulations of the inner accretion flow of Sagittarius A* fuelled by stellar winds",
abstract = "We present ATHENA++ grid-based, hydrodynamic simulations of accretion on to Sagittarius A* via the stellar winds of the ~30Wolf-Rayet stars within the central parsec of the galactic centre. These simulations spa{\~n}4 orders ofmagnitude in radius, reaching all the way down to 300 gravitational radii of the black hole, ~32 times further than in previous work. We reproduce reasonably well the diffuse thermal X-ray emission observed by Chandra in the central parsec. The resulting accretion flow at small radii is a superposition of two components: (1) a moderately unbound, sub-Keplerian, thick, pressure-supported disc that is at most (but not all) times aligned with the clockwise stellar disc, and (2) a bound, low-angular momentum inflow that proceeds primarily along the southern pole of the disc. We interpret this structure as a natural consequence of a few of the innermost stellar winds dominating accretion, which produces a flow with a broad distribution of angular momentum. Including the star S2 in the simulation has a negligible effect on the flow structure. Extrapolating our results from simulations with different inner radii, we find an accretion rate of approximately a few ×10-8M⊙ yr-1 at the horizon scale, consistent with constraints based on modelling the observed emission of Sgr A*. The flow structure found here can be used as more realistic initial conditions for horizon scale simulations of Sgr A*.",
keywords = "Accretion, Accretion discs, Black hole physics, Galaxy: centre, Hydrodynamics, Rayet, Stars: Wolf, X-rays: ISM",
author = "Ressler, {S. M.} and E. Quataert and Stone, {James McLellan}",
note = "Funding Information: We thank the anonymous referee for several helpful comments. We thank C. Gammie, J. Cuadra, J. R. Lu, R. Genzel, S. Gillessen, and K. El-Badry for useful discussions, as well as all the members of the horizon collaboration, http://horizon.astro.illinois.edu, for their advice and encouragement. We thank F. Baganoff for making the Chandra X-ray data available to us for use in comparison to our simulations. We thank D. Fielding for advice and help on plotting formats and give a double portion of thanks to C. J. White for his frequent aid in using the ATHENA++ code. Finally, we thank N. M. Lemaster and P. F. Hopkins for freely providing the preliminary coding framework that we built upon to calculate the stellar wind source terms. This work was supported in part by National Science Foundation (NSF) grants AST 13-33612, AST 1715054, AST-1715277, Chandra theory grant TM7-18006X from the Smithsonian Institution, a Simons Investigator award from the Simons Foundation, and by the NSF through the eXtreme Science and Engineering Discovery Environment computational time allocation TG-AST090038 on San Diego Supercomputer Center Comet. SMR is supported in part by the National Aeronautics and Space Administration Earth and Space Science Fellowship. This work was made possible by computing time granted by University of California Berkeley on the Savio cluster. Funding Information: We thank the anonymous referee for several helpful comments. We thank C. Gammie, J. Cuadra, J. R. Lu, R. Genzel, S. Gillessen, and K. El-Badry for useful discussions, as well as all the members of the horizon collaboration, http://horizon.astro.illinois.edu, for their advice and encouragement. We thank F. Baganofffor making the Chandra X-ray data available to us for use in comparison to our simulations. We thank D. Fielding for advice and help on plotting formats and give a double portion of thanks to C. J. White for his frequent aid in using the ATHENA++ code. Finally, we thank N. M. Lemaster and P. F. Hopkins for freely providing the preliminary coding framework that we built upon to calculate the stellarwind source terms. This work was supported in part by National Science Foundation (NSF) grants AST 13-33612, AST 1715054, AST-1715277, Chandra theory grant TM7-18006X from the Smithsonian Institution, a Simons Investigator award from the Simons Foundation, and by the NSF through the eXtreme Science and Engineering Discovery Environment computational time allocation TG-AST090038 on San Diego Supercomputer Center Comet. SMR is supported in part by the National Aeronautics and Space Administration Earth and Space Science Fellowship. This work was made possible by computing time granted by University of California Berkeley on the Savio cluster. Publisher Copyright: {\textcopyright} 2018 The Author(s).",
year = "2018",
month = aug,
day = "1",
doi = "10.1093/MNRAS/STY1146",
language = "English (US)",
volume = "478",
pages = "3544--3563",
journal = "Monthly Notices of the Royal Astronomical Society",
issn = "0035-8711",
publisher = "Oxford University Press",
number = "3",
}