H2CO Distribution and Formation in the TW HYA Disk

H2CO is one of the most readily detected organic molecules in protoplanetary disks. Yet its distribution and dominant formation pathway(s) remain largely unconstrained. To address these issues, we present ALMA observations of two H2CO lines ( and ) at 0 5 (∼30 au) spatial resolution toward the disk around the nearby T Tauri star TW Hya. Emission from both lines is spatially resolved, showing a central depression, a peak at 0 4 radius, and a radial decline at larger radii with a bump at ∼1″, near the millimeter continuum edge. We adopt a physical model for the disk and use toy models to explore the radial and vertical H2CO abundance structure. We find that the observed emission implies the presence of at least two distinct H2CO gas reservoirs: (1) a warm and unresolved inner component (