2025ApJ...984L..10G

An analysis of the gaseous component in protoplanetary disks can inform us about their thermal and physical structure, chemical composition, and kinematic properties, all of which are crucial for understanding various processes within the disks. By exploiting the asymmetry of the line emission, or via line profile analysis, we can locate the emitting surfaces. Here, we present the emission surfaces of the exoALMA sources in ¹²CO J = 3-2, ¹³CO J = 3-2, and CS J = 7-6. We find that ¹²CO traces the upper disk atmosphere, with mean 〈z/r〉 values of ≈0.28, while ¹³CO and CS trace lower regions of the disk with mean 〈z/r〉 values of ≈0.16 and ≈0.18, respectively. We find that ¹²CO 〈z/r〉 and the disk mass are positively correlated with each other; this relationship offers a straightforward way to infer the disk mass. We derive 2D r - z temperature distributions of the disks. Additionally, we search for substructure in the surfaces and radial intensity profiles; we find evidence of localized substructure in the emission surfaces and peak intensity profiles of nearly every disk, with this substructure often being coincident between molecular tracers, intensity profiles, and kinematic perturbations. Four disks display evidence of potential photodesorption, implying that this effect may be common even in low far-ultraviolet star-forming regions. For most disks, we find that the physical and thermal structure is more complex than analytical models can account for, highlighting a need for more theoretical work and a better understanding of the role of projection effects on our observations.