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 , mean peculiar motion of the sources with respect to Galactic rotation (U src , V src , W src ), 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 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 Galacto-centric 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 .

Large-scale Molecular Gas Distribution in the M17 Cloud Complex: Dense Gas Conditions of Massive Star Formation?

“…Parallax distances of 1.83 +0.08 −0.07 kpc and 1.98 +0.14 −0.12 kpc by maser monitoring have been determined towards two dust clumps in M17, G014.63-00.57 and G015.03-00.57, respectively (Honma et al 2012;Wu et al 2014). These parallax distances are larger than photometric distances of 1.3 ± 0.4 kpc (Hanson et al 1997) and 1.6 ± 0.3 kpc (Nielbock et al 2001), obtained by the analysis of the main-sequence OB stars.…”

The Galaxy in Context: Structural, Kinematic, and Integrated Properties

“…Model-based estimates. vlbi astrometry has provided accurate parallaxes and proper motions for over 100 OH, SiO, and Methanol masers in High Mass Star Formation Regions (HMSFR) in the Galactic disk (Honma et al 2007(Honma et al , 2012Reid et al 2009aReid et al , 2014Sato et al 2010). Most of these sources are located in the Galactic spiral arms.…”

Photometric, kinematic, and variability study in the young open cluster NGC 1960

“…Using the cluster Galactic positions and distance, we obtained the Galactocentric distance of the cluster NGC 1960 as R G = 9.25 kpc. Here, R ⊙ , the distance between the Sun and the Galactic Centre, is considered as 8.0±0.3 kpc (Honma et al 2012;Camarillo et al 2018). It is difficult to estimate an accurate value of M C without identifying all the low-mass members.…”