Fundamental Parameters of the Milky Way Galaxy Based on VLBI astrometry
Abstract
We present analyses to determine the fundamental parameters of the Galaxy based on VLBI astrometry of 52 Galactic maser sources obtained with VERA, VLBA, and EVN. We model the Galaxy's structure with a set of parameters, including the Galaxy center distance R0, the angular rotation velocity at the LSR Ω0, the mean peculiar motion of the sources with respect to Galactic rotation (Usrc, Vsrc, Wsrc), the rotation-curve shape index, and the V component of the Solar peculiar motions, V⊙. Based on a Markov chain Monte-Carlo method, we find that the Galaxy center distance is constrained at a 5% level to be R0 = 8.05 ± 0.45 kpc, where the error bar includes both statistical and systematic errors. We also find that the two components of the source peculiar motion Usrc and Wsrc are fairly small compared to the Galactic rotation velocity, being Usrc = 1.0 ± 1.5 km s-1 and Wsrc = -1.4 ± 1.2 km s-1. Also, the rotation curve shape is found to be basically flat between Galacto-centric radii of 4 and 13 kpc. On the other hand, we find a linear relation between Vsrc and V⊙ as Vsrc = V⊙ - 19 (± 2) km s-1, suggesting that the value of Vsrc is fully dependent on the adopted value of V⊙. Regarding the rotation speed in the vicinity of the Sun, we also find a strong correlation between Ω0 and V⊙. We find that the angular velocity of the Sun, Ω⊙, which is defined as Ω⊙ ≡ Ω0 + V⊙/R0, can be well constrained with the best estimate of Ω⊙ = 31.09 ± 0.78 km s-1 kpc-1. This corresponds to Θ0 = 238 ± 14 km s-1 if one adopts the above value of R0 and recent determination of V⊙ ∼ 12 km s-1.
- Publication:
-
Publications of the Astronomical Society of Japan
- Pub Date:
- December 2012
- DOI:
- 10.1093/pasj/64.6.136
- arXiv:
- arXiv:1211.3843
- Bibcode:
- 2012PASJ...64..136H
- Keywords:
-
- astrometry;
- Galaxy: Galactic parameters;
- VLBI;
- Astrophysics - Astrophysics of Galaxies
- E-Print:
- 14 pages, 6 figures, PASJ in press