Using gas clouds to probe the accretion flow around Sgr A: G2's delayed pericentre passage

We study the dynamical evolution of the putative gas clouds G1 and G2 recently discovered in the Galactic Centre. Following earlier studies suggesting that these two clouds are part of a larger gas streamer, we combine their orbits into a single trajectory. Since the gas clouds experience a drag for...

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Bibliographic Details
Published in:Monthly notices of the Royal Astronomical Society 2017-02, Vol.465 (2), p.2310-2310
Main Authors: Madigan, Ann-Marie, McCourt, Michael, O'Leary, Ryan M
Format: Article
Language:English
Subjects:
Accretion
Accretion disks
Astronomy
Clouds
Delay
Drag force
Monitoring
Orbits
Precession
Star & galaxy formation
Trajectories
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Summary:We study the dynamical evolution of the putative gas clouds G1 and G2 recently discovered in the Galactic Centre. Following earlier studies suggesting that these two clouds are part of a larger gas streamer, we combine their orbits into a single trajectory. Since the gas clouds experience a drag force from background gas, this trajectory is not exactly Keplerian. Assuming the G1 and G2 clouds trace this trajectory, we fit for the drag force they experience and thus extract information about the accretion flow at a distance of thousands of Schwarzschild radii from the black hole. This range of radii is important for theories of black hole accretion, but is currently unconstrained by observations. In this paper, we extend our previous work by accounting for radial forces due to possible inflow or outflow of the background gas. Such radial forces drive precession in the orbital plane, allowing a slightly better fit to the G1 and G2 data. This precession delays the pericentre passage of G2 by 4-5 months relative to estimates derived from a Keplerian orbital fit; if it proves possible to identify the pericentre time observationally, this enables an immediate test of whether G1 and G2 are gas clouds part of a larger gas streamer. If G2 is indeed a gas cloud, its closest approach likely occurred in late summer 2014, after many of the observing campaigns monitoring G2's anticipated pericentre passage ended. We discuss how this affects interpretation of the G2 observations.
ISSN:0035-8711
1365-2966
DOI:10.1093/mnras/stw2815