Spirals and vertical motions in the planet-forming disk around HD 100546

Context . The disk around the Herbig star HD 100546 represents a particularly interesting target for the study of dynamical planet–disk interactions, as various features observed in both the dust and gas provide direct and indirect evidence for ongoing planet formation. Aims . In this work, we aim to characterize the gas kinematics of five molecular CO emission lines ( 12 CO 7–6, 12 CO 3–2, 12 CO 2–1, 13 CO 2–1, C 18 O 2–1), observed with ALMA in HD 100546, to reveal deviations from Keplerian rotation, along with substructures in the peak intensity and line width. Methods . For our analysis, we fit the molecular intensity channels with the DISCMINER package to model the line profiles and extract observables such as the centroid velocity, peak intensity, and line width. In addition to fitting the full cube, we also conducted runs where the blue- and redshifted sides were modeled separately to search for possible asymmetries. Results . Our analysis reveals prominent kinematical spiral features in all five lines on large scales of the disk and we were able to reproduce their morphology with both a linear and logarithmic spiral. In 12 CO 2–1, spirals are also seen in the peak intensity residuals, while the line width residuals exhibit a prominent ring of enhanced line widths around 125–330 au. The models further show that the emission from the redshifted side may originate from higher disk layers than that from the blueshifted side, with the asymmetry being especially pronounced for 12 CO 7–6. Conclusions . The pitch angles of the spirals are consistent with those driven by an embedded companion inside of 50 au, suggesting a dynamical mechanism rather than gravitational instabilities. Furthermore, we found indications of a companion around 90–150 au, where tentative dips are present in the radial profiles of the integrated intensity of 13 CO and C 18 O 2–1 and pressure minima are observed in the azimuthal velocities. For the first time, we also detected downward vertical flows in this region, which coincide with the observed dust gap. The asymmetry in the emission heights could be a result of infall from the disk’s environment. Another explanation could be the presence of a warped inner disk casting a shadow onto one side of the disk.