Kawata, D; Bovy, J; Matsunaga, N; Baba, J; (2019) Galactic rotation from Cepheids with Gaia DR2 and effects of non-axisymmetry. Monthly Notices of the Royal Astronomical Society , 482 (1) pp. 40-51. 10.1093/mnras/sty2623.

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Abstract

We apply a simple axisymmetric disc model to 218 Galactic Cepheids whose accurate measurements of the distance and velocities are obtained by cross-matching an existing Cepheids catalogue with the Gaia DR2 data. Our model fit determines the ‘local centrifugal speed’, Vc – defined as the rotation speed required to balance the local radial gravitational force – at the Sun’s location to be Vc(R0) = 236 ± 3 km s−1 and the Sun’s azimuthal and radial peculiar motions to be V⊙ = 12.4 ± 0.7 km s−1 and U⊙ = 7.7 ± 0.9 km s−1, respectively. These results are obtained with strong priors on the solar radius, R0 = 8.2 ± 0.1 kpc, and the Sun’s angular rotation velocity, Ω⊙ = 30.24 ± 0.12 km s−1 kpc−1. We also applied the axisymmetric model to mock data from a N-body/hydrodynamic simulation of a Milky Way-like galaxy with a bar and spiral arms. We find that our axisymmetric model fit to the young stars recovers the local centrifugal speed reasonably well, even in the face of significant non-axisymmetry. However, the local centrifugal speed determined from our Cepheid sample could suffer from systematic uncertainty as large as 6 km s−1.

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