Constraining the Galactic bar and spiral pattern speeds with the Hyades tidal stream

TL;DR

This study uses N-body simulations and Gaia data to constrain the Milky Way's bar and spiral pattern speeds by analyzing the Hyades tidal stream's structure.

Contribution

It introduces a simulation-based method to estimate Galactic pattern speeds using open cluster streams, aligning models with Gaia observations.

Findings

Models with specific pattern speeds match the observed Hyades stream density

Faster bar models do not reproduce the observed stream structure

Results support a relatively slow Galactic bar, consistent with recent constraints

Abstract

We present a suite of direct $N$-body simulations of the Hyades open cluster and its tidal stream in a Milky Way potential that includes a rotating bar and spiral arms. Using the high-resolution code PETAR and an AGAMA-based multi-component Galactic model, we vary the bar and spiral pattern speeds ($\Omega_b$, $\Omega_s$) on a discrete grid and quantify the resulting changes in stream orientation, length, and internal density structure. We compare the simulations to Gaia EDR3 using the convergent point (CP) and compact convergent point (CCP) methods, followed by an adaptive three-dimensional nearest-neighbor matching in Cartesian space $(x,y,z)$. The Gaia candidate members exhibit a pronounced longitudinal density peak at $Y_{\mathrm{rot}} \approx 0.1\,\mathrm{kpc}$ in a stream-aligned coordinate system. Models with $\Omega_s = 22.5\,\mathrm{km\,s^{-1}\,kpc^{-1}}$ and $\Omega_b \simeq 40$--$45\,\mathrm{km\,s^{-1}\,kpc^{-1}}$ best reproduce this feature, while faster-bar models fail to match the observed density structure. These models are consistent with recent constraints favoring a relatively slow Galactic bar, and they illustrate how nearby open-cluster streams can provide an independent, local constraint on non-axisymmetric Galactic dynamics.