arXiv subjects

Gianni Cataldi

Publications and source records attributed to Gianni Cataldi.

At least 37 records · Page 2Linked to original sources

arXiv2025

exoALMA. VI. Rotating under Pressure: Rotation curves, azimuthal velocity substructures, and pressure variations

The bulk motion of the gas in protoplanetary disks around newborn stars is nearly Keplerian. By leveraging the high angular and spectral resolution of ALMA, we can detect small-scale velocity perturbations in molecular line observations caused by local gas pressure variations in the disk, possibly induced by embedded protoplanets. This paper presents the azimuthally averaged rotational velocity and its deviations from Keplerian rotation ($δ\upsilon_ϕ$) for the exoALMA sample, as measured in the $^{12}$CO and $^{13}$CO emission lines. The rotation signatures show evidence for vertically stratified disks, in which $^{13}$CO rotates faster than $^{12}$CO due to a distinct thermal gas pressure gradient at their emitting heights. We find $δ\upsilon_ϕ$-substructures in the sample on both small ($\sim$10 au) and large ($\sim$100 au) radial scales, reaching deviations up to 15% from background Keplerian velocity in the most extreme cases. More than 75% of the rings and 80% of the gaps in the dust continuum emission resolved in $δ\upsilon_ϕ$ are co-located with gas pressure maxima and minima, respectively. Additionally, gas pressure substructures are observed far beyond the dust continuum emission. For the first time, we determined the gas pressure derivative at the midplane from observations and found it to align well with the dust substructures within the given uncertainties. Based on our findings, we conclude that gas pressure variations are likely the dominant mechanism for ring and gap formation in the dust continuum.

astro-ph.EP↗

arXiv2025

exoALMA. XVII. Characterizing the Gas Dynamics around Dust Asymmetries

The key planet-formation processes in protoplanetary disks remain an active matter of research. One promising mechanism to radially and azimuthally trap millimeter-emitting dust grains, enabling them to concentrate and grow into planetesimals, is anticyclonic vortices. While dust observations have revealed crescent structures in several disks, observations of their kinematic signatures are still lacking. Studying the gas dynamics is, however, essential to confirm the presence of a vortex and understand its dust trapping properties. In this work, we make use of the high-resolution and sensitivity observations conducted by the exoALMA large program to search for such signatures in the $^{12}$CO and $^{13}$CO molecular line emission of four disks with azimuthal dust asymmetries: HD 135344B, HD 143006, HD 34282, and MWC 758. To assess the vortex features, we constructed an analytical vortex model and performed hydrodynamical simulations. For the latter, we assumed two scenarios: a vortex triggered at the edge of a dead zone and of a gap created by a massive embedded planet. These models reveal a complex kinematical morphology of the vortex. When compared to the data, we find that none of the sources show a distinctive vortex signature around the dust crescents in the kinematics.

astro-ph.EP↗

arXiv2025

exoALMA XV: Interpreting the height of CO emission layer

The availability of exquisite data and the development of new analysis techniques have enabled the study of emitting heights in proto-planetary disks. In this paper we introduce a simple model linking the emitting height of CO to the disk surface density and temperature structure. We then apply the model to measurements of the emitting height and disk temperature conducted as part of exoALMA, integrated with additional legacy measurements from the MAPS Large Programme, to derive CO column densities and surface density profiles (assuming a CO abundance) for a total of 14 disks. A unique feature of the method we introduce to measure surface densities is that it can be applied to optically thick observations, rather than optically thin as conventionally done. While we use our method on a sample of well studied disks where temperature structures have been derived using two emission lines, we show that reasonably accurate estimates can be obtained also when only one molecular transition is available. With our method we obtain independent constraints from $^{12}$CO and $^{13}$CO and we find they are in general good agreement using the standard $^{12}$C/$^{13}$C isotopic ratio. The masses derived from our method are systematically lower compared with the values derived dynamically from the rotation curve if using an ISM CO abundance, implying that CO is depleted by a median factor $\sim$20 with respect to the ISM value, in line with other works that find that CO is depleted in proto-planetary disks.

astro-ph.EP↗

arXiv2025

exoALMA. VIII. Probabilistic Moment Maps and Data Products using Non-parametric Linear Models

Extracting robust inferences on physical quantities from disk kinematics measured from Doppler-shifted molecular line emission is challenging due to the data's size and complexity. In this paper we develop a flexible linear model of the intensity distribution in each frequency channel, accounting for spatial correlations from the point spread function. The analytic form of the model's posterior enables probabilistic data products through sampling. Our method debiases peak intensity, peak velocity, and line width maps, particularly in disk substructures that are only partially resolved. These are needed in order to measure disk mass, turbulence, pressure gradients, and to detect embedded planets. We analyse HD 135344B, MWC 758, and CQ Tau, finding velocity substructures 50--200 ${\rm m s^{-1}}$ greater than with conventional methods. Additionally, we combine our approach with discminer in a case study of J1842. We find that uncertainties in stellar mass and inclination increase by an order of magnitude due to the more realistic noise model. More broadly, our method can be applied to any problem requiring a probabilistic model of an intensity distribution conditioned on a point spread function.

astro-ph.EP↗

arXiv2025

exoALMA V: Gaseous Emission Surfaces and Temperature Structures

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 $^{12}$CO $J=3-2$, $^{13}$CO $J=3-2$, and CS $J=7-6$. We find that $^{12}$CO traces the upper disk atmosphere, with mean <$z/r$> values of $\approx$ 0.28, while $^{13}$CO and CS trace lower regions of the disk with mean values of $\approx$ 0.16 and $\approx$ 0.18, respectively. We find that $^{12}$CO <$z/r$> and the disk mass are positively correlated with each other; this relationship offers a straightforward way to infer the disk mass. We derive 2-D $r-z$ 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 co-incident between molecular tracers, intensity profiles, and kinematic perturbations. Four disks display evidence of potential photo-desorption, implying that this effect may be common even in low FUV 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.

astro-ph.EP↗

arXiv2025

exoALMA III: Line-intensity Modeling and System Property Extraction from Protoplanetary Disks

The ALMA large program exoALMA offers a unique window into the three-dimensional physical and dynamical properties of 15 circumstellar disks where planets may be actively forming. Here, we present an analysis methodology to map the gas disk structure and substructure encoded in 12CO, 13CO, and CS line emission from our targets. To model and characterize the disk structure probed by optically thin species, such as CS and, in some cases, 13CO, we introduce a composite line profile kernel that accounts for increased intensities caused by the projected overlap between the disk's front and back side emission. Our workflow, built on the Discminer modelling framework, incorporates an improved iterative two-component fitting method for inclined sources ($i>40^\circ$), to mitigate the impact of the disk backside on the extraction of velocity maps. Also, we report best-fit parameters for the Keplerian stellar masses, as well as inclinations, position angles, systemic velocities, rotation direction, and emission surfaces of the disks in our sample.

astro-ph.EP↗

arXiv2025

exoALMA IX: Regularized Maximum Likelihood Imaging of Non-Keplerian Features

The planet-hunting ALMA large program exoALMA observed 15 protoplanetary disks at ~0.15" angular resolution and ~100 m/s spectral resolution, characterizing disk structures and kinematics in enough detail to detect non-Keplerian features (NKFs) in the gas emission. As these features are often small and low-contrast, robust imaging procedures are critical for identifying and characterizing NKFs, including determining which features may be signatures of young planets. The exoALMA collaboration employed two different imaging procedures to ensure the consistent detection of NKFs: CLEAN, the standard iterative deconvolution algorithm, and regularized maximum likelihood (RML) imaging. This paper presents the exoALMA RML images, obtained by maximizing the likelihood of the visibility data given a model image and subject to regularizer penalties. Crucially, in the context of exoALMA, RML images serve as an independent verification of marginal features seen in the fiducial CLEAN images. However, best practices for synthesizing RML images of multi-channeled (i.e. velocity-resolved) data remain undefined, as prior work on RML imaging for protoplanetary disk data has primarily addressed single-image cases. We used the open source Python package MPoL to explore RML image validation methods for multi-channeled data and synthesize RML images from the exoALMA observations of 7 protoplanetary disks with apparent NKFs in the 12CO J=3-2 CLEAN images. We find that RML imaging methods independently reproduce the NKFs seen in the CLEAN images of these sources, suggesting that the NKFs are robust features rather than artifacts from a specific imaging procedure.

astro-ph.EP↗

arXiv2025

exoALMA I. Science Goals, Project Design and Data Products

Planet formation is a hugely dynamic process requiring the transport, concentration and assimilation of gas and dust to form the first planetesimals and cores. With access to extremely high spatial and spectral resolution observations at unprecedented sensitivities, it is now possible to probe the planet forming environment in detail. To this end, the exoALMA Large Program targeted fifteen large protoplanetary disks ranging between ${\sim}1\arcsec$ and ${\sim}7\arcsec$ in radius, and mapped the gas and dust distributions. $^{12}$CO J=3-2, $^{13}$CO J=3-2 and CS J=7-6 molecular emission was imaged at high angular (${\sim}~0\farcs15$) and spectral (${\sim}~100~{\rm m\,s^{-1}}$) resolution, achieving a surface brightness temperature sensitivity of ${\sim}1.5$~K over a single channel, while the 330~GHz continuum emission was imaged at 90~mas resolution and achieved a point source sensitivity of ${\sim}\,40~μ{\rm Jy~beam^{-1}}$. These observations constitute some of the deepest observations of protoplanetary disks to date. Extensive substructure was found in all but one disk, traced by both dust continuum and molecular line emission. In addition, the molecular emission allowed for the velocity structure of the disks to be mapped with excellent precision (uncertainties on the order of $10~{\rm m\,s^{-1}}$), revealing a variety of kinematic perturbations across all sources. From this sample it is clear that, when observed in detail, all disks appear to exhibit physical and dynamical substructure indicative of on-going dynamical processing due to young, embedded planets, large-scale, (magneto-)hydrodynamical instabilities or winds.

astro-ph.EP↗

arXiv2025

exoALMA. X. channel maps reveal complex $^{12}$CO abundance distributions and a variety of kinematic structures with evidence for embedded planets

We analyze the $^{12}$CO $J=3-2$ data cubes of the disks in the exoALMA program. 13/15 disks reveal a variety of kinematic substructures in individual channels: large-scale arcs or spiral arms, localized velocity kinks, and/or multiple faints arcs that appear like filamentary structures on the disk surface. We find kinematic signatures that are consistent with planet wakes in six disks: AA Tau, SY Cha, J1842, J1615, LkCa 15 and HD 143006. Comparison with hydrodynamical and radiative transfer simulations suggests planets with orbital radii between 80 and 310\,au and masses between 1 and 5 M$_\mathrm{Jup}$. Additional kinematic substructures limit our ability to place tight constraints on the planet masses. When the inclination is favorable to separate the upper and lower surfaces (near 45$^\mathrm{o}$, i.e. in 7/15 disks), we always detect the vertical CO snowline and find that the $^{12}$CO freeze-out is partial in the disk midplane, with a depletion factor of $\approx 10^{-3}$ - $10^{-2}$ compared to the warm molecular layer. In these same seven disks, we also systematically detect evidence of CO desorption in the outer regions.

astro-ph.EP↗

arXiv2025

exoALMA XII: Weighing and sizing exoALMA disks with rotation curve modelling

The exoALMA large program offers a unique opportunity to investigate the fundamental properties of protoplanetary disks, such as their masses and sizes, providing important insights in the mechanism responsible for the transport of angular momentum. In this work, we model the rotation curves of CO isotopologues $^{12}$CO and $^{13}$CO of ten sources within the exoALMA sample, and we constrain the stellar mass, the disk mass and the density scale radius through precise characterization of the pressure gradient and disk self gravity. We obtain dynamical disk masses for our sample measuring the self-gravitating contribution to the gravitational potential. We are able to parametrically describe their surface density, and all of them appear gravitationally stable. By combining dynamical disk masses with dust continuum emission data, we determine an averaged gas-to-dust ratio of approximately 400, not statistically consistent with the standard value of 100, assuming optically thin dust emission. In addition, the measurement of the dynamical scale radius allows for direct comparison with flux-based radii of gas and dust. This comparison suggests that substructures may influence the size of the dust disk, and that CO depletion might reconcile our measurements with thermochemical models. Finally, with the stellar mass, disk mass, scale radius, and accretion rate, and assuming self-similar evolution of the surface density, we constrain the effective $α_S$ for these systems. We find a broad range of $α_S$ values ranging between $10^{-5}$ and $10^{-2}$.

astro-ph.EP↗

arXiv2025

exoALMA IV: Substructures, Asymmetries, and the Faint Outer Disk in Continuum Emission

The exoALMA Large Program targeted a sample of 15 disks to study gas dynamics within these systems, and these observations simultaneously produced continuum data at 0.9 mm (331.6 GHz) with exceptional surface brightness sensitivity at high angular resolution. To provide a robust characterization of the observed substructures, we performed a visibility space analysis of the continuum emission from the exoALMA data, characterizing axisymmetric substructures and nonaxisymmetric residuals obtained by subtracting an axisymmetric model from the observed data. We defined a nonaxisymmetry index and found that the most asymmetric disks predominantly show an inner cavity and consistently present higher values of mass accretion rate and near-infrared excess. This suggests a connection between outer disk dust substructures and inner disk properties. The depth of the data allowed us to describe the azimuthally averaged continuum emission in the outer disk, revealing that larger disks (both in dust and gas) in our sample tend to be gradually tapered compared to the sharper outer edge of more compact sources. Additionally, the data quality revealed peculiar features in various sources, such as shadows, inner disk offsets, tentative external substructures, and a possible dust cavity wall.

astro-ph.EP↗

arXiv2024

Detection of Dimethyl Ether in the Central Region of the MWC 480 Protoplanetary Disk

Characterizing the chemistry of complex organic molecules (COMs) at the epoch of planet formation provides insights into the chemical evolution of the interstellar medium (ISM) and the origin of organic materials in our Solar System. We report a detection of dimethyl ether (CH$_3$OCH$_3$) in the disk around the Herbig Ae star MWC 480 with the sensitive Atacama Large Millimeter/submillimeter Array observations. This is the first detection of CH$_3$OCH$_3$ in a non-transitional Class II disk. The spatially unresolved, compact (${\lesssim}$25 au in radius) nature, the broad line width ($\sim$30 km s$^{-1}$), and the high excitation temperature (${\sim}$200 K) indicate sublimation of COMs in the warm inner disk. Despite the detection of CH$_3$OCH$_3$, methanol (CH$_3$OH), the most abundant COM in the ISM, has not been detected, from which we constrain the column density ratio of CH$_3$OCH$_3$/CH$_3$OH ${\gtrsim}$7. This high ratio may indicate the reprocessing of COMs during the disk phase, as well as the effect of the physical structure in the inner disk. We also find that this ratio is higher than in COM-rich transition disks recently discovered. This may indicate that, in the full disk of MWC 480, COMs have experienced substantial chemical reprocessing in the innermost region, while the COM emission in the transition disks predominantly traces the inherited ice sublimating at the dust cavity edge located at larger radii (${\gtrsim}$20 au).

astro-ph.EP↗

arXiv2024

JWST-MIRI Spectroscopy of Warm Molecular Emission and Variability in the AS 209 Disk

We present MIRI MRS observations of the large, multi-gapped protoplanetary disk around the T-Tauri star AS 209. The observations reveal hundreds of water vapor lines from 4.9 to 25.5 $μ$m towards the inner $\sim1$ au in the disk, including the first detection of ro-vibrational water emission in this disk. The spectrum is dominated by hot ($\sim800$ K) water vapor and OH gas, with only marginal detections of CO$_2$, HCN, and a possible colder water vapor component. Using slab models with a detailed treatment of opacities and line overlap, we retrieve the column density, emitting area, and excitation temperature of water vapor and OH, and provide upper limits for the observable mass of other molecules. Compared to MIRI spectra of other T-Tauri disks, the inner disk of AS 209 does not appear to be atypically depleted in CO$_2$ nor HCN. Based on \textit{Spitzer IRS} observations, we further find evidence for molecular emission variability over a 10-year baseline. Water, OH, and CO$_2$ line luminosities have decreased by factors 2-4 in the new MIRI epoch, yet there are minimal continuum emission variations. The origin of this variability is yet to be understood.

astro-ph.EP↗

arXiv2023

A Primordial Origin for the Gas-Rich Debris Disks Around Intermediate-Mass Stars

While most debris disks consist of dust with little or no gas, a fraction has significant amounts of gas detected via emission lines of CO, ionized carbon, and/or atomic oxygen. Almost all such gaseous debris disks known are around A-type stars with ages up to 50 Myr. We show, using semi-analytic disk evolution modeling, that this can be understood if the gaseous debris disks are remnant protoplanetary disks that have become depleted of small grains compared to the interstellar medium. Photoelectric heating by the A-stars' FUV radiation is then inefficient, while the stars' EUV and X-ray emissions are weak owing to a lack of surface convective zones capable of driving magnetic activity. In this picture, stars outside the range of spectral types from A through early B are relatively hard to have such long-lived gas disks. Less-massive stars have stronger magnetic activity in the chromosphere, transition region, and corona with resulting EUV and X-ray emission, while more-massive stars have photospheres hot enough to produce strong EUV radiation. In both cases, primordial disk gas is likely to photoevaporate well before 50 Myr. These results come from 0D disk evolution models where we incorporate internal accretion stresses, MHD winds, and photoevaporation by EUV and X-ray photons with luminosities that are functions of the stellar mass and age. A key issue this work leaves open is how some disks become depleted in small dust so that FUV photoevaporation slows. Candidates include grains' growth, settling, radial drift, radiation force, and incorporation into planetary systems.

astro-ph.EP↗

arXiv2023

MAPS: Constraining Serendipitous Time Variability in Protoplanetary Disk Molecular Ion Emission

Theoretical models and observations suggest that the abundances of molecular ions in protoplanetary disks should be highly sensitive to the variable ionization conditions set by the young central star. We present a search for temporal flux variability of HCO+ J=1-0, which was observed as a part of the Molecules with ALMA at Planet-forming Scales (MAPS) ALMA Large Program. We split out and imaged the line and continuum data for each individual day the five sources were observed (HD 163296, AS 209, GM Aur, MWC 480, and IM Lup, with between 3 to 6 unique visits per source). Significant enhancement (>3σ) was not observed, but we find variations in the spectral profiles in all five disks. Variations in AS 209, GM Aur, and HD 163296 are tentatively attributed to variations in HCO+ flux, while variations in IM Lup and MWC 480 are most likely introduced by differences in the \textit{uv} coverage, which impact the amount of recovered flux during imaging. The tentative detections and low degree of variability are consistent with expectations of X-ray flare driven HCO+ variability, which requires relatively large flares to enhance the HCO+ rotational emission at significant (>20%) levels. These findings also demonstrate the need for dedicated monitoring campaigns with high signal to noise ratios to fully characterize X-ray flare driven chemistry.

astro-ph.EP↗

arXiv2023

Primordial or Secondary? Testing models of debris disk gas with ALMA

The origin and evolution of gas in debris disks is still not well understood. Secondary gas production from cometary material or a primordial origin have been proposed. So far, observations have mostly concentrated on CO, with only few C observations available. We create an overview of the C and CO content of debris disk gas and use it test state-of-the-art models. We use new and archival ALMA observations of CO and CI emission, complemented by CII data from Herschel, for a sample of 14 debris disks. This expands the number of disks with ALMA measurements of both CO and CI by ten disks. We present new detections of CI emission towards three disks: HD 21997, HD 121191 and HD 121617. We use a simple disk model to derive gas masses and column densities. We find that current state-of-the-art models of secondary gas production overpredict the neutral carbon content of debris disk gas. This does not rule out a secondary origin, but might indicate that the models require an additional C removal process. Alternatively, the gas might be produced in transient events rather than a steady-state collisional cascade. We also test a primordial gas origin by comparing our results to a simplified thermo-chemical model. This yields promising results, but more detailed work is required before a conclusion can be reached. Our work demonstrates that the combination of C and CO data is a powerful tool to advance our understanding of debris disk gas.

astro-ph.EP↗

arXiv2023

Molecules with ALMA at Planet-forming Scales (MAPS). Complex Kinematics in the AS 209 Disk Induced by a Forming Planet and Disk Winds

We study the kinematics of the AS 209 disk using the J=2-1 transitions of $^{12}$CO, $^{13}$CO, and C$^{18}$O. We derive the radial, azimuthal, and vertical velocity of the gas, taking into account the lowered emission surface near the annular gap at ~1.7 (200 au) within which a candidate circumplanetary disk-hosting planet has been reported previously. In $^{12}$CO and $^{13}$CO, we find a coherent upward flow arising from the gap. The upward gas flow is as fast as $150~{\rm m~s}^{-1}$ in the regions traced by $^{12}$CO emission, which corresponds to about 50% of the local sound speed or $6\%$ of the local Keplerian speed. Such an upward gas flow is difficult to reconcile with an embedded planet alone. Instead, we propose that magnetically driven winds via ambipolar diffusion are triggered by the low gas density within the planet-carved gap, dominating the kinematics of the gap region. We estimate the ambipolar Elsasser number, Am, using the HCO$^+$ column density as a proxy for ion density and find that Am is ~0.1 at the radial location of the upward flow. This value is broadly consistent with the value at which numerical simulations find ambipolar diffusion drives strong winds. We hypothesize the activation of magnetically-driven winds in a planet-carved gap can control the growth of the embedded planet. We provide a scaling relationship which describes the wind-regulated terminal mass: adopting parameters relevant to 100 au from a solar-mass star, we find the wind-regulated terminal mass is about one Jupiter mass, which may help explain the dearth of directly imaged super-Jovian-mass planets.

astro-ph.EP↗

arXiv2022

Molecules with ALMA at Planet-forming Scales (MAPS). A Circumplanetary Disk Candidate in Molecular Line Emission in the AS 209 Disk

We report the discovery of a circumplanetary disk (CPD) candidate embedded in the circumstellar disk of the T Tauri star AS 209 at a radial distance of about 200 au (on-sky separation of 1."4 from the star at a position angle of $161^\circ$), isolated via $^{13}$CO $J=2-1$ emission. This is the first instance of CPD detection via gaseous emission capable of tracing the overall CPD mass. The CPD is spatially unresolved with a $117\times82$ mas beam and manifests as a point source in $^{13}$CO, indicating that its diameter is $\lesssim14$ au. The CPD is embedded within an annular gap in the circumstellar disk previously identified using $^{12}$CO and near-infrared scattered light observations, and is associated with localized velocity perturbations in $^{12}$CO. The coincidence of these features suggests that they have a common origin: an embedded giant planet. We use the $^{13}$CO intensity to constrain the CPD gas temperature and mass. We find that the CPD temperature is $\gtrsim35$ K, higher than the circumstellar disk temperature at the radial location of the CPD, 22 K, suggesting that heating sources localized to the CPD must be present. The CPD gas mass is $\gtrsim 0.095 M_{\rm Jup} \simeq 30 M_{\rm Earth}$ adopting a standard $^{13}$CO abundance. From the non-detection of millimeter continuum emission at the location of the CPD ($3σ$ flux density $\lesssim26.4~μ$Jy), we infer that the CPD dust mass is $\lesssim 0.027 M_{\rm Earth} \simeq 2.2$ lunar masses, indicating a low dust-to-gas mass ratio of $\lesssim9\times10^{-4}$. We discuss the formation mechanism of the CPD-hosting giant planet on a wide orbit in the framework of gravitational instability and pebble accretion.

astro-ph.EP↗