Constraining the pitch angle of the Galactic spiral arms in the Milky Way

TL;DR

This paper analyzes various measurements of the Milky Way's spiral arm pitch angles, compiling a catalog, comparing methods, and examining historical data to improve understanding of galactic structure.

Contribution

It provides a comprehensive catalog of spiral arm pitch angles and assesses measurement consistency over decades, highlighting methodological improvements.

Findings

Increased ratio of primary to secondary peaks in recent data

Reduced discrepancies in pitch angle measurements over time

Histograms show convergence of results since 2015

Abstract

We carry out analyses of some parameters of the galactic spiral arms, in the currently available samples. We present a catalog of the observed pitch angle for each spiral arm in the Milky Way disk. For each long spiral arm in the Milky Way, we investigate for each individual arm its pitch angle, as measured through different methods (parallaxes, twin-tangent arm, kinematical, etc), and assess their answers. Second, we catalog recent advances in the cartography of the Galaxy (global mean arm pitch, arm number, arm shape, interarm distance at the Sun). We statistically compare the results over a long time frame, from 1980 to 2017. Histograms of about 90 individual results published in recent years (since mid-2015) are compared to 66 earlier results (from 1980 to 2005), showing the ratio of primary to secondary peaks to have increased by almost a factor of 3. Similarly, many earlier discrepancies (expressed in r.m.s.) have been reduced by almost a factor 3.