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  Identifying resonances of the Galactic bar in Gaia DR2: II. Clues from angle space

H. Trick, W. (2021). Identifying resonances of the Galactic bar in Gaia DR2: II. Clues from angle space. Monthly Notices of the Royal Astronomical Society, 509(1), 844-865. doi:10.1093/mnras/stab2866.

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H. Trick, Wilma1, Author           
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1Computational Structure Formation, MPI for Astrophysics, Max Planck Society, ou_2205642              

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 Abstract: The Milky Way disc exhibits intricate orbit substructure of still debated dynamical origin. The angle variables (θϕ, θR) – which are conjugates to the actions (Lz, JR), and describe a star’s location along its orbit – are a powerful diagnostic to identify l:m resonances via the orbit shape relation ΔθR/Δθϕ = −m/l. In the past, angle signatures have been hidden by survey selection effects (SEs). Using test particle simulations of a barred galaxy, we demonstrate that Gaia should allow us to identify the Galactic bar’s outer Lindblad resonance (OLR;l = +1, m = 2) in angle space. We investigate strategies to overcome SEs. In the angle data of the Gaia Data Release 2 (DR2) Radial Velocity Spectrometer (RVS) sample, we independently identify four candidates for the OLR and therefore for the pattern speed Ωbar. The strongest candidate, Ωbar ∼ 1.4Ω0, positions the OLR above the ‘Sirius’ moving group, agrees with measurements from the Galactic Centre, and might be supported by higher order resonances around the ‘Hercules/Horn’. But it misses the classic orbit orientation flip, as discussed in the companion study on actions. The candidate Ωbar ∼ 1.2Ω0 was also suggested by the action-based study, has the OLR at the ‘Hat’, is consistent with slow bar models, but still affected by SEs. Weaker candidates are Ωbar = 1.6Ω0 and 1.74Ω0. In addition, we show that the stellar angles do not support the ‘Hercules/Horn’ being created by the OLR of a fast bar. We conclude that – to resolve if ‘Sirius’ or ‘Hat’ is related to the bar’s OLR – more complex dynamical explanations and more extended data with well-behaved SEs are required.

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Language(s): eng - English
 Dates: 2021-10-07
 Publication Status: Published online
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 Rev. Type: Peer
 Identifiers: DOI: 10.1093/mnras/stab2866
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Title: Monthly Notices of the Royal Astronomical Society
  Abbreviation : Mon. Not. Roy. Astron. Soc.
Source Genre: Journal
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Pages: - Volume / Issue: 509 (1) Sequence Number: - Start / End Page: 844 - 865 Identifier: ISSN: 0035-8711
ISSN: 1365-8711