The Stellar "Snake" I: Whole Structure and Properties

TL;DR

This paper maps and analyzes the full extent and properties of the young, snake-like stellar structure in the solar neighborhood using Gaia EDR3 data, revealing its coherent age, metallicity, and expansion dynamics.

Contribution

It provides the first comprehensive mapping and dynamical analysis of the entire stellar structure, linking its formation history to a filamentary molecular cloud.

Findings

The structure contains over ten thousand stars and 13 embedded open clusters.

It is a coherent, 30-40 Myr old stellar population with solar metallicity.

The structure is expanding coherently with an age consistent with its stellar age.

Abstract

To complement our previous discovery of the young snake-like structure in the solar neighborhood and reveal the structure's full extent, we build two samples of stars within the Snake and its surrounding territory from {\tt Gaia EDR3}. With the friends-of-friends algorithm, we identify 2694 and 9615 Snake member candidates from the two samples. Thirteen open clusters are embedded in these member candidates. By combining the spectroscopic data from multiple surveys, we investigate the comprehensive properties of the candidates and find that they \thj{are very likely to} belong to one sizable structure, since most of the components are well bridged in their spatial distributions, and follow a single stellar population with an age of $30-40$\,Myr and solar metallicity. This sizable structure is best explained as hierarchically primordial, and probably formed from a filamentary giant molecular cloud with unique formation history in localized regions. To analyze the dynamics of the Snake, we divide the structure into five groups according to their tangential velocities; we find that the groups are expanding at a coherent rate ($\kappa_X\sim3.0\,\times10^{-2}\,\rm km\,s^{-1}\,pc^{-1}$) along the length of the structure ($X$-direction). \thj{The corresponding expansion age ($\tau\sim33$\,Myr) is highly consistent with the age of the Snake}. With over ten thousand member stars, the Snake is an ideal laboratory to study nearby coeval stellar formation, stellar physics, and environmental evolution over a large spatial extent.