The uncertainty in Galactic parameters

TL;DR

This paper reanalyzes measurements of galactic masers to better understand key parameters of the Milky Way, revealing model-dependent estimates and emphasizing the importance of the Sun's peculiar velocity correction.

Contribution

It provides a likelihood-based reanalysis of galactic parameters using maser data, highlighting the dependence on rotation curve models and revising the Sun's peculiar velocity.

Findings

Best fit models suggest higher Sun peculiar velocity (V_sol) around 11 km/s.

Galactic center distance R_0 varies from 6.7 to 8.9 kpc depending on the model.

The ratio v_0/R_0 is well constrained between 29.9 and 31.6 km/s/kpc.

Abstract

We reanalyse the measurements of parallax, proper motion, and line-of-sight velocity for 18 masers in high mass star-forming regions presented by Reid et al. (2009). We use a likelihood analysis to investigate the distance of the Sun from the Galactic centre, R_0, the rotational speed of the local standard of rest, v_0, and the peculiar velocity of the Sun, vsol, for various models of the rotation curve, and models which allow for a typical peculiar motion of the high mass star-forming regions. We find that these data are best fit by models with non-standard values for vsol or a net peculiar motion of the high mass star-forming regions. We argue that a correction to vsol is much more likely, and that these data support the conclusion of Binney (2009) that V_sol should be revised upwards from 5.2 km/s to 11 km/s. We find that the values of R_0 and v_0 that we determine are heavily dependent on the model we use for the rotation curve, with model-dependent estimates of R_0 ranging from 6.7 \pm 0.5kpc to 8.9 \pm 0.9kpc, and those of v_0 ranging from 200 \pm 20 km/s to 279 \pm 33 km/s. We argue that these data cannot be thought of as implying any particular values of R_0 or v_0. However, we find that v_0/R_0 is better constrained, lying in the range 29.9-31.6 km/s/kpc for all models but one.