Clustering of Local Group distances: publication bias or correlated measurements? V. Galactic rotation constants

TL;DR

This study compiles and analyzes 162 measurements of the Galactic rotation speed to assess potential biases and derive updated Galactic constants, highlighting differences based on tracer populations and providing refined values for the Milky Way's rotation parameters.

Contribution

The paper presents the most comprehensive database of Galactic rotation speed measurements and offers updated, more accurate Galactic rotation constants considering tracer-dependent variations.

Findings

No evidence of publication bias in recent measurements.

Significant differences in rotation speed based on tracer populations.

Updated Galactic rotation constants with statistical and systematic uncertainties.

Abstract

As part of on an extensive data mining effort, we have compiled a database of 162 Galactic rotation speed measurements at $R_0$ (the solar Galactocentric distance), $\Theta_0$. Published between 1927 and 2017 June, this represents the most comprehensive set of $\Theta_0$ values since the 1985 meta analysis that led to the last revision of the International Astronomical Union's recommended Galactic rotation constants. Although we do not find any compelling evidence of the presence of `publication bias' in recent decades, we find clear differences among the $\Theta_0$ values and the $\Theta_0/R_0$ ratios resulting from the use of different tracer populations. Specifically, young tracers (including OB and supergiant stars, masers, Cepheid variables, H{\sc ii} regions, and young open clusters), as well as kinematic measurements of Sgr A* near the Galactic Center, imply a significantly larger Galactic rotation speed at the solar circle and a higher $\Theta_0/R_0$ ratio (i.e., $\Theta_0 = 247 \pm 3$ km s$^{-1}$ and $\Theta_0/R_0 = 29.81 \pm 0.32$ km s$^{-1}$ kpc$^{-1}$; statistical uncertainties only) than any of the tracers dominating the Galaxy's mass budget (i.e., field stars and the H{\sc i}/CO distributions). Using the latter as most representative of the bulk of the Galaxy's matter distribution, we arrive at an updated set of Galactic rotation constants, $\Theta_0 = 225 \pm 3 \mbox{ (statistical)} \pm 10 \mbox{ (systematic) km s}^{-1}$, $R_0 = 8.3 \pm 0.2 \mbox{ (statistical)} \pm 0.4 \mbox{ (systematic) kpc}$, and $\Theta_0 / R_0 = 27.12 \pm 0.39 \mbox{ (statistical)} \pm 1.78 \mbox{ (systematic) km s}^{-1} \mbox{ kpc}^{-1}$.