Gas content and evolution of a sample of YSO associations at d ≲ 3.5 kpc from the Sun

Young Stellar Objects (YSO) are newly formed stars from molecular clouds. They stay close to where they were born and serve as good tracers to study gas and star formation. During cloud evolution, young massive stars can disrupt the surrounding gas through stellar feedback, changing the gas distribution. We study the distribution of the gas around a sample of YSO associations located at d ≲ 3.5 kpc from the Sun by comparing the location and morphology between ^12CO (J = 1-0) emission, Planck 870 μm maps and YSO associations. Based on the spatial distribution of the gas compared to that of the YSOs, we classify the YSO associations into six types: direct, close, bubble, complex, diffuse, and clean associations. The complex associations are large structures consisting of both gas-rich and gas-poor segments. We study the velocity dispersion-size relation toward different association types. From the ratio between different types, we estimate a feedback time of ≈ 1.7 Myr in the solar neighborhood. The sample sets a solid foundation to explore the relationship between interstellar medium evolution, star formation, and Galaxy structure.