Birth Sites of Young Stellar Associations and Recent Star Formation in a Flocculent Corrugated Disk

TL;DR

This study traces the birth locations of young stellar associations in the solar neighborhood, revealing their origins in a corrugated molecular disk and their relation to spiral arm dynamics and vertical gas motions.

Contribution

It provides the first orbit-based estimates of birth sites for young stellar groups, linking their origins to a corrugated molecular disk and spiral arm interactions.

Findings

Most associations formed inside the Sun's galactocentric radius.

Associations are located between peaks in UV stellar velocity distribution.

Birth sites are aligned with peaks in the vertical phase space distribution.

Abstract

With backwards orbit integration we estimate birth locations of young stellar associations and moving groups identified in the solar neighborhood that are younger than 70 Myr. The birth locations of most of these stellar associations are at smaller galactocentric radius than the Sun, implying that their stars moved radially outwards after birth. Exceptions to this rule include are the Argus and Octans associations which formed outside the Sun's Galactocentric radius. Variations in birth heights of the stellar associations suggest that they were born in a corrugated disk of molecular clouds, similar to that inferred from the current filamentary molecular cloud distribution and dust extinction maps. Multiple spiral arm features with different but near corotation pattern speeds and at different heights could account for the stellar association birth sites. We find that the young stellar associations are located in between peaks in the UV stellar velocity distribution for stars in the solar neighborhood. This would be expected if they were born in a spiral arm which perturbs stellar orbits that cross it. In contrast, stellar associations seem to be located near peaks in the vertical phase space distribution, suggesting that the gas in which stellar associations are born moves vertically together with the low velocity dispersion disk stars.