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 R_{0}, the angular rotation velocity at the LSR Ω_{0}, the mean peculiar motion of the sources with respect to Galactic rotation (U_{src}, V_{src}, W_{src}), the rotationcurve shape index, and the V component of the Solar peculiar motions, V_{⊙}. Based on a Markov chain MonteCarlo method, we find that the Galaxy center distance is constrained at a 5% level to be R_{0} = 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 U_{src} and W_{src} are fairly small compared to the Galactic rotation velocity, being U_{src} = 1.0 ± 1.5 km s^{1} and W_{src} = 1.4 ± 1.2 km s^{1}. Also, the rotation curve shape is found to be basically flat between Galactocentric radii of 4 and 13 kpc. On the other hand, we find a linear relation between V_{src} and V_{⊙} as V_{src} = V_{⊙}  19 (± 2) km s^{1}, suggesting that the value of V_{src} 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 Ω_{0} and V_{⊙}. We find that the angular velocity of the Sun, Ω_{⊙}, which is defined as Ω_{⊙} ≡ Ω_{0} + V_{⊙}/R_{0}, can be well constrained with the best estimate of Ω_{⊙} = 31.09 ± 0.78 km s^{1} kpc^{1}. This corresponds to Θ_{0} = 238 ± 14 km s^{1} if one adopts the above value of R_{0} 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
 EPrint:
 14 pages, 6 figures, PASJ in press