Molecular gas structure encodes key information about the physical processes involved in giant molecular cloud (GMC) formation and collapse, as well as their response to stellar feedback. While a large number of studies have systematically characterized the physical properties of individual GMCs, their spatial distribution and surrounding gas structure have been less extensively studied. In this talk, I will present a novel method for characterizing in-situ gas structure by stacking radial profiles. For GMCs, we measure the CO(2–1) profile around each GMC peak position and obtain stacked representative intensity profiles for GMCs in different environments and with different physical properties. Our stacked intensity profiles can generally be characterized as a combination of two Gaussians plus a constant, with the broad Gaussian component reflecting the degree of surrounding gas concentration and being more prominent around more massive and gravitationally bound GMCs. We also stack CO(2–1) intensity profiles around PHANGS-HST star clusters of different masses and ages. We find that star clusters spatially associated with H II regions show the highest CO(2–1) concentration, with a cluster formation efficiency from gas of ∼1%. Clusters older than 4 Myr show a flat intensity profile, indicating the role of stellar feedback in clearing gas on such a short timescale. We demonstrate that our method works effectively on high-resolution observations of large samples, providing a general and quantitative description of in-situ gas structure, and can serve as a benchmark for simulations of star formation from molecular gas to star clusters.
