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 O0, 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 = 8.050.45 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 = 1.01.5 km s-1 andWsrc = -1.41.2 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 O0 and V. We find that the angular velocity of the Sun, O, which is defined as O0 + V=R0, can be well constrained with the best estimate of O = 31.090.78 km s-1 kpc-1. This corresponds to T0 = 23814 km s-1if one adopts the above value of R0 and recent determination of V 12 km s-1. © 2012. Astronomical Society of Japan.