Andres F. Izquierdo

Constraining the total mass of protoplanetary disks is crucial for determining the amount of material available for planet formation. Yet providing accurate measurements of the disk mass is challenging. Investigating the gas dynamics provides a powerful tracer-independent method to precisely characterize disk masses. By fitting the velocity rotation curves of different molecular tracers with an accurate model including the thermal stratification and self-gravity of the disk, we constrained the stellar masses, disk masses, and scale radii for the disks around HD 97048 and WaOph 6. We obtained M _⋆ = 2.226 _−0.049 ^+0.054 M _⊙ , M _d = 0.3 _−0.061 ^+0.055 M _⊙ , and R _c = 172 ₋₁₄ ⁺²⁴ au for HD 97048 and M _⋆ = 0.956 _−0.006 ^+0.006 M _⊙ , M _d = 0.21 _−0.038 ^+0.045 M _⊙ , and R _c = 647 ₋₁₅₅ ⁺¹⁹³ au for WaOph 6. We also measured the corresponding gas-to-dust and disk-to-star mass ratios. We efficiently extended the dynamical method to characterize embedded sources exhibiting features of absorption, for which a careful analysis is required to avoid biases in the retrieved velocity profiles. We prove the importance of including a beam smearing correction to the curves. If not included, this observational effect can systematically bias the velocity profiles, thus altering the disk mass estimates up to ≈45%. We provide comprehensive estimates of the systematic uncertainties on the best-fit parameters by bootstrapping over both the retrieved geometry and 2D thermal structure of the two disks. The overall uncertainty on the disk masses is ≈20%. Finally, we investigated the connection between disk stability and the appearance of spiral morphologies in the millimeter continuum emission by comparing the Toomre parameter of all dynamically weighed disks to date, demonstrating that disks with millimeter-dust spirals have systematically lower values of Q .

Hints of planet formation have been independently reported within the gap of the disc around 2MASS-J16120668–301027 from millimetre continuum, infrared, and H$\alpha$ observations. In this work, we present new evidence for ongoing planet formation based on Atacama Large Millimeter/submillimeter Array (ALMA) Band 7 observations, detecting 0.87 mm dust continuum emission together with $^{12}$CO (J = 3–2) and $^{13}$CO (J = 3–2) line emission. Visibility modelling of the continuum data reveals an inner disc and two dust rings peaking at 23 and 75 au. The continuum morphology is better reproduced by an eccentric disc model ($e\sim 0.1$) than by an axisymmetric disc. We further investigate the gas kinematics through modelling of the $^{12}$CO channel maps. The residual line-width map shows a localized increase in velocity dispersion at the position of a previously reported circumplanetary disc candidate (deprojected radius $\sim$32 au, position angle $\sim 170^\circ$) and along its orbit. This signal is spatially coincident with kink-like features and a transition from sub-Keplerian to super-Keplerian velocities. In addition, the velocity residual map exhibits an arc-like structure extending outward from the planet candidate, while the gas kinematics – despite substantial uncertainties – is consistent with inflow towards the candidate’s orbital radius. The observed increase in velocity dispersion agrees with predictions from planet–disc interaction simulations, which produce enhanced turbulence both at the planet location and along its orbital path. Taken together, the continuum morphology and gas kinematic signatures provide compelling new evidence for ongoing planet formation within the disc gap.

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.

The exoALMA large program provided an unprecedented view of the morphologies and kinematics of 15 circumstellar disks, offering a biased but homogenous and well-characterized sample for population-level analysis. Continuum observations revealed numerous dust substructures, known to be potential signatures of embedded planets. We analyze the observed dust morphologies with the simulation-based inference tool DBNets2.0, assuming these are due to embedded planets at fixed locations, to infer the system’s properties. We estimate the putative planet mass, the disk α viscosity, scale height, and dust Stokes number that would reproduce 19 substructures in 13 of the 15 exoALMA disks. We compare our results with literature estimates derived with different methods, and find good agreement in most cases. We further explore the implications of the inferred disk properties for accretion, showing that for the Herbig stars in our sample, the implied viscous accretion timescales are too long to account for their observed stellar accretion rates. Regarding planet migration, our results favor inward migration, with only three putative planets expected to migrate outward. Finally, we check for correlations of the inferred disk and planet properties with the disks’ gas-to-dust mass ratio, nonaxisymmetry index, and masses of the gas, dust, and host stars, finding no remarkable trends.

Protoplanetary disks are the birthplaces of planetary systems, and deviations from Keplerian rotation imprinted in disk gas kinematics serve as key tracers of physical processes and the presence of protoplanets within disks. Using the CO ( J = 3–2) data from the exoALMA Large Program, encompassing 15 disks, we constructed two-dimensional (2D) maps of centroid velocity, line width, and peak intensity, and extracted non-Keplerian deviations by subtracting smooth Keplerian models. This Letter provides the first systematic and uniform overview of 2D gas substructures across the entire exoALMA sample. We find that all targets exhibit large-scale deviations from smooth Keplerian disks, displaying a variety of morphologies, including spiral-like structures, arc- or ring-like features, and patterns indicative of variations in the emitting surface height. Nonaxisymmetric spiral-arm features are detected or suggested in five disks (CQ Tau, MWC 758, HD 135344B, HD 34282, and SY Cha), and are preferentially found in Herbig Ae/Fe systems. In contrast, some other sources (J1852, PDS 66, and V4046 Sgr), despite exhibiting noticeable deviations, appear to be dynamically quieter. This 2D atlas suggests that kinematic substructures are ubiquitous in large (≳100 au) protoplanetary disks with ages of a few million years, based on the observations obtained with sufficient sensitivity at a moderate-to-high spatial resolution of ∼20 au and high-velocity resolution of ∼0.1 km s ⁻¹ .

Vertical gas flows—such as winds and meridional circulations—are natural outcomes of protoplanetary disk processes and play a critical role in the earliest stages of planet formation. We analyze the vertical gas motions in 14 disks, as part of the exoALMA Large Program, focusing on the ¹² CO J = 3–2 and ¹³ CO J = 3–2 emission lines. Using discminer to model the Keplerian velocity field, we extract line-of-sight velocity residuals and measure the radial and vertical components of the gas motion. Vertical motions are detected in most disks. Two types of patterns emerge: (1) oscillatory up/down flows, likely linked to instabilities; and (2) transitions from downward to upward motions that we interpret as the bases of disk winds. In most cases, the velocity amplitudes are of a few tens of m s ⁻¹ . However, two disks, MWC758 and CQ Tau, show two spiral velocity features in their residual maps, red- and blueshifted, which we interpret as vertical velocities reaching up to ∼350 m s ⁻¹ (∼0.7 c _s ), consistent with the gas motion in eccentric disks. Fast upward motions (up to 500 m s ⁻¹ ; ∼1.8 c _s ) are also detected in the outer disk of MWC758. Synthetic observations from (magneto)hydrodynamic simulations validate the reliability of our method. Although strong molecular winds appear to be relatively rare in ¹² CO and ¹³ CO, our study shows that, when traced by deep high-spectral-resolution line data, protoplanetary disks exhibit ubiquitous vertical flows. However, their overall velocity structure is highly complex, preventing the identification of a coherent dominant physical mechanism driving the vertical motions across all disks, thus requiring further theoretical investigation.

The exoALMA Large Program has revealed a wealth of substructures in the dust and molecular line emission of several protoplanetary discs, suggesting that planet formation may unfold within highly dynamic environments. Using synthetic observations of planet–disk interactions and disk instabilities, we demonstrate how the origin of these substructures can be investigated through a tomographic study of molecular lines, extending the scope of the analysis beyond line-centroid kinematics alone. Our results indicate that with only a few hours of ALMA integration at moderate angular resolution ( 0 . ″ 15 − 0 . ″ 30 ), it is possible to identify the key signatures driven by planets more massive than 0.1% of the stellar mass. These signatures manifest not only as deviations from Keplerian motion but also as localized line broadening, enabling accurate constraints on the orbital radius and azimuthal location of the planets. We further show that a diagnostic based on line skewness in spectrally resolved observations can help distinguish between planetary and instability-driven signatures, owing to the distinct degrees of velocity coherence associated with each mechanism. Finally, we apply this tomographic analysis to exoALMA CO line data for the disks of HD 135344B and MWC 758. In HD 135344B, we identify strongly localized velocity and line-width perturbations, suggesting the possibility of three massive planets embedded in the disk: one at R = 95 au, exterior to the continuum substructures, and two within dust gaps at R = 41 au and R = 73 au. For MWC 758, the dominance of vertical-velocity spirals over localized signatures is consistent with predictions from models of moderate disk eccentricities or warps, potentially induced by a substellar companion in the inner regions of the system.

Aims . We present the first high-resolution (∼0″.14) Atacama Large Millimeter/submillimeter Array (ALMA) Band 6 dust continuum, ¹² CO J = 2-1, ¹³ CO J = 2-1, and C ¹⁸ O J = 2-1 molecular line emission observations of the quadruple system HD 34700. In particular, HD34700AaAb is a spectroscopic binary ( M _bin = 4 M _⊙ ) surrounded by two low-mass companions (B = 0.6 M _⊙ , C = 0.4 M _⊙ ) at large separations. Its circumbinary disk is highly substructured, featuring numerous spiral arms and a large cavity observed in infrared (IR) scattered light. We aim to shed light on the nature of these features by examining the gas kinematics at work in the circumbinary disk. Methods . We analyzed the CO line channel and intensity moment maps. By fitting a Keplerian model to the line channel emission, we identified the residual motions and conducted a line spectra analysis. Results . We resolved an asymmetric continuum crescent on top of a dust ring at 0739 (138 au) colocated with the IR ring. The CO molecule’s line emission traces a smaller cavity in gas, whose edge aligns with the inner rim of the ring detected in Hα emission at 0″.20 (65 au). The ¹² CO line emission and kinematics trace highly non-Keplerian motions (∼0.1Δυ _k ) and these CO spiral features align well with the spiral structures in scattered light. The ¹² CO line spectra analysis reveals a streamer above the southeastern disk plane, likely falling onto the disk. The ¹³ CO and C ¹⁸ O kinematics largely follow the disk’s underlying Keplerian rotation, while ¹³ CO exhibits tentative signs of anticyclonic vortex flows at the continuum crescent location. Conclusions . Our multimolecular line study suggests that the circumbinary disk of HD 34700A is highly perturbed in its upper layers, possibly warped and influenced by infalling material. While late-stage infall may account for the IR spirals and the formation of the vortex through Rossby wave instability, an embedded massive companion within the cavity might also be contributing to these features.

Turbulence is expected to transport angular momentum and drive mass accretion in protoplanetary disks. One way to directly measure turbulent motion in disks is through molecular line broadening. DM Tau is one of only a few disks with claimed detection of nonthermal line broadening of 0.25 c _s –0.33 c _s , where c _s is the sound speed. Using the radiative transfer code mcfost within a Bayesian inference framework that evaluates over five million disk models to efficiently sample the parameter space, we fit high-resolution ( 0 . ″ 15 , 28 m s ⁻¹ ) ¹² CO J = 3–2 observations of DM Tau from the exoALMA Large Program. This approach enables us to simultaneously constrain the disk structure and kinematics, revealing a significant nonthermal contribution to the line width of ∼0.4 c _s , inconsistent with purely thermal motions. Using the CO-based disk structure as a starting point, we reproduce the CS J = 7–6 emission well, demonstrating that the CS (which is more sensitive to nonthermal motions than CO) agrees with the turbulence inferred from the CO fit. Establishing a well-constrained background disk model further allows us to identify residual structures in the moment maps that deviate from the expected emission, revealing localized perturbations that may trace forming planets. This framework provides a powerful general approach for extracting disk structure and nonthermal broadening directly from molecular line data and can be applied to other disks with high-quality observations.