arXiv subjects

Ryuta Orihara

Publications and source records attributed to Ryuta Orihara.

26 records · Page 2Linked to original sources

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↗

arXiv2023

ALMA Band 6 high-resolution observations of the transitional disk around SY Cha

In this study, we reported the results of high-resolution (0.14 arcsec) Atacama Large Millimeter/submillimeter Array (ALMA) observations of the 225 GHz dust continuum and CO molecular emission lines from the transitional disk around SY Cha. Our high-resolution observations clearly revealed the inner cavity and the central point source for the first time. The radial profile of the ring can be approximated by a bright narrow ring superimposed on a fainter wide ring. Furthermore, we found that there is a weak azimuthal asymmetry in dust continuum emission. For gas emissions, we detected $\rm{}^{12}CO$(2$-$1), $\rm{}^{13}CO$(2$-$1) and $\rm{}C^{18}O$(2$-$1), from which we estimated the total gas mass of the disk to be $2.2\times10^{-4}M_\odot$, assuming a CO/H$_2$ ratio of $10^{-4}$. The observations showed that the gas is present inside the dust cavity. The analysis of the velocity structure of the $\rm{}^{12}CO$(2$-$1) emission line revealed that the velocity is distorted at the location of the dust inner disk, which may be owing to warping of the disk or radial gas flow within the cavity of the dust disk. High-resolution observations of SY Cha showed that this system is composed of a ring and a distorted inner disk, which may be common, as indicated by the survey of transitional disk systems at a resolution of $\sim$0.1~arcsec.

astro-ph.EP↗