Gaps, Rings, and Non-Axisymmetric Structures in Protoplanetary Disks - From Simulations to ALMA Observations (1411.2736v2)

Abstract: Recent observations by the Atacama Large Millimeter/submillimeter Array (ALMA) of disks around young stars revealed distinct asymmetries in the dust continuum emission. In this work we want to study axisymmetric and non-axisymmetric structures, evocated by the magneto-rotational instability in the outer regions of protoplanetary disks. We combine the results of state-of-the-art numerical simulations with post-processing radiative transfer (RT) to generate synthetic maps and predictions for ALMA. We performed non-ideal global 3D MHD stratified simulations of the dead-zone outer edge using the FARGO MHD code PLUTO. The stellar and disk parameters are taken from a parameterized disk model applied for fitting high-angular resolution multi-wavelength observations of circumstellar disks. The 2D temperature and density profiles are calculated consistently from a given surface density profile and Monte-Carlo radiative transfer. The 2D Ohmic resistivity profile is calculated using a dust chemistry model. The magnetic field is a vertical net flux field. The resulting dust reemission provides the basis for the simulation of observations with ALMA. The fiducial model develops a large gap followed by a jump in surface density located at the dead-zone outer edge. The jump in density and pressure is strong enough to stop the radial drift of particles. In addition, we observe the generation of vortices by the Rossby wave instability (RWI) at the jumps location close to 60 AU. The vortices are steadily generated and destroyed at a cycle of 40 local orbits. The RT results and simulated ALMA observations predict the feasibility to observe such large scale structures appearing in magnetized disks without having a planet.

• The paper presents a novel approach using non-ideal global 3D MHD simulations coupled with radiative transfer methods to link MRI phenomena to observable disk features.
• It identifies MRI-induced gaps, enhanced surface density at dead-zone edges, and cyclic vortex formations at around 60 AU influenced by varying dust-to-gas ratios.
• The findings stress the challenge of distinguishing MRI-induced structures from planetary-induced gaps and point to future improvements in simulation and observational resolution.

Analysis of "Gaps, rings, and non-axisymmetric structures in protoplanetary disks - from simulations to ALMA observations"

The paper presents a comprehensive paper of protoplanetary disks, focusing on the structures formed by magneto-rotational instability (MRI) and their observability with the Atacama Large Millimeter/submillimeter Array (ALMA). The authors utilize a combination of advanced numerical simulations and radiative transfer methods to model these astrophysical phenomena, shedding light on the intricate dynamics within protoplanetary disks.

Methodology

The research employs non-ideal global 3D magnetohydrodynamic (MHD) simulations, executed via the FARGO MHD code PLUTO, to investigate the outer regions of protoplanetary disks. These regions are characterized by significant activity due to the MRI, particularly at the dead-zone outer edges. For the simulations, key parameters include a stellar mass of $0.5 M_\odot$ and a total disk mass of $0.085 M_*$, under differing dust-to-gas mass ratios of $10^{-2}$ and $10^{-4}$ to paper varying levels of magnetic coupling.

The radiative transfer simulations, crucial for generating synthetic maps for ALMA, are performed using the MC3D code. By linking the MHD simulations to observable phenomena via radiative transfer simulations, the authors seek to establish predictions for ALMA's ability to detect these structures.

Results

The research identifies that both models transitioned rapidly into a turbulent state, spurred by MRI, with significant dynamic difference manifesting based on the dust-to-gas ratio. The fiducial model with a ratio of $10^{-2}$ revealed a substantial gap and a marked increase in surface density at the outer dead-zone edge, halting radial drift and generating vortices due to the Rossby wave instability at around 60 AU. This dynamic activity periodically generated and destroyed these vortices over cycles of 40 local orbits. These structures, possibly observable by ALMA, point to the complexity within these regions absent planetary influences.

Implications and Future Research

The findings underscore the importance of distinguishing between gaps formed by MRI-related processes and those potentially formed by planetary bodies. This paper highlights that while current technology like ALMA can detect large-scale structures in magnetized disks, distinguishing between MRI-induced and planetary-induced gaps remains challenging. Future work could focus on improving the resolution of such observations or integrating additional physical processes in simulations, like dynamical resistivity or other magnetic diffusion terms (e.g., ambipolar and Hall effects), to better understand the implications of these structures in disk evolution and planet formation.

Additionally, the research opens avenues to investigate the accumulation and dynamics of larger particles within these structures, which could be pertinent for understanding planetesimal formation. With further advancements in observational techniques and simulation models, enhanced clarity on these disk structures will potentially lead to significant insights into the early stages of planetary system formation.