A Case against a Significant Detection of Precession in the Galactic Warp

TL;DR

This paper challenges recent claims of significant warp precession in the Milky Way by demonstrating that accounting for population age differences negates the need for precession, suggesting the warp may not precess.

Contribution

It shows that previous detections of warp precession were likely due to model assumptions, and provides a revised analysis indicating no significant precession when population age is considered.

Findings

Warp precession is consistent with zero within uncertainties.

Older stellar populations show lower warp amplitudes.

No compelling evidence for warp precession when accounting for population differences.

Abstract

Recent studies of warp kinematics using Gaia DR2 data have produced detections of warp precession for the first time, which greatly exceeds theoretical predictions of models. However, this detection assumes a warp model derived for a young population (few tens of megayears) to fit velocities of an average older stellar population of the thin disk (several gigayears) in Gaia-DR2 observations, which may lead to unaccounted systematic errors. Here, we recalculate the warp precession with the same approach and Gaia DR2 kinematic data, but using different warp parameters based on the fit of star counts of the Gaia DR2 sample, which has a much lower warp amplitude than the young population. When we take into account this variation of the warp amplitude with the age of the population, we find that there is no need for precession. We find the value of warp precession $\beta = 4^{+6}_{-4}$ km s$^{-1}$ kpc$^{-1}$, which does not exclude nonprecessing warp.