A Young, Low-Density Stellar Stream in the Milky Way Disk: Theia 456

TL;DR

This paper characterizes Theia 456, a young, low-density stellar stream in the Milky Way disk, revealing its common age, chemical homogeneity, and disk membership, suggesting such streams may be widespread and inform star formation history.

Contribution

The study provides detailed analysis of Theia 456, demonstrating its properties and potential ubiquity, which advances understanding of stellar streams in the Milky Way disk.

Findings

Theia 456 is a 200 pc long, young stellar stream in the Milky Way disk.

Members share a common age of approximately 175 million years.

The stream shows chemical homogeneity with [Fe/H] = -0.07 dex.

Abstract

Our view of the variety of stellar structures pervading the local Milky Way has been transformed by the application of clustering algorithms to the Gaia catalog. In particular, several stellar streams have been recently discovered that are comprised of hundreds to thousands of stars and span several hundred parsecs. We analyze one such structure, Theia 456, a low-density stellar stream extending nearly 200 pc and 20$^{\circ}$ across the sky. By supplementing Gaia astrometric data with spectroscopic metallicities from LAMOST and photometric rotation periods from the Zwicky Transient Facility (ZTF) and the Transiting Exoplanet Survey Satellite (TESS), we establish Theia 456's radial velocity coherence, and we find strong evidence that members of Theia 456 have a common age ($\simeq$175 Myr), common dynamical origin, and formed from chemically homogeneous pre-stellar material ([Fe/H] = $-$0.07 dex). Unlike well-known stellar streams in the Milky Way, which are in its halo, Theia 456 is firmly part of the thin disk. If our conclusions about Theia 456 can be applied to even a small fraction of the remaining $\simeq$8300 independent structures in the Theia catalog, such low-density stellar streams may be ubiquitous. We comment on the implications this has for the nature of star-formation throughout the Galaxy.