Measuring protoplanetary disk gas surface density profiles with ALMA

Abstract

The gas and dust are spatially segregated in protoplanetary disks due to the vertical settling and radial drift of large grains. A fuller accounting of the mass content and distribution in disks therefore requires spectral line observations. We extend the modeling approach presented in Williams & Best (2014) to show that gas surface density profiles can be measured from high fidelity 13CO integrated intensity images. We demonstrate the methodology by fitting ALMA observations of the HD 163296 disk to determine a gas mass, Mgas = 0.048 solar masse, and accretion disk characteristic size Rc = 213au and gradient gamma = 0.39. The same parameters match the C18O 2--1 image and indicates an abundance ratio [13CO]/[C18O] of 700 independent of radius. To test how well this methodology can be applied to future line surveys of smaller, lower mass T Tauri disks, we create a large 13CO 2--1 image library and fit simulated data. For disks with gas masses 3-10 Jupiter masses at 150pc, ALMA observations with a resolution of 0.2-0.3 arcseconds and integration times of about 20 minutes allow reliable estimates of Rc to within about 10au and gamma to within about 0.2. Economic gas imaging surveys are therefore feasible and offer the opportunity to open up a new dimension for studying disk structure and its evolution toward planet formation.

22 pages, 9 figures, submitted to ApJ, available here in the case the ALMA TAC want to see it

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• The Host Galaxies of Tidal Disruption Events
• Gas vs dust sizes of protoplanetary disks: effects of dust evolution
• Systematic Variations of CO Gas Abundance with Radius in Gas-rich Protoplanetary Disks
• Dust settling and rings in the outer regions of protoplanetary discs subject to ambipolar diffusion
• Ring formation and dust dynamics in wind-driven protoplanetary discs: global simulations
• The First Detection of 13C17O in a Protoplanetary Disk: a Robust Tracer of Disk Gas Mass
• Probing the Protosolar Disk Using Dust Filtering at Gaps in the Early Solar System
• New Constraints From Dust Lines On The Surface Densities Of Protoplanetary Disks
• The determination of protoplanetary disk masses
• Mass constraints for 15 protoplanetary disks from HD 1-0
• Grand challenges in protoplanetary disc modelling
• Using Ice and Dust Lines to Constrain the Surface Densities of Protoplanetary Disks
• Gas mass tracers in protoplanetary disks: CO is still the best
• Depletion of gaseous CO in protoplanetary disks by surface-energy-regulated ice formation
• Probing the protoplanetary disk gas surface density distribution with ${}^{13}$CO emission
• Pebbles in an Embedded Protostellar Disk: The Case of CB26
• Size-polydisperse dust in molecular gas: Energy equipartition versus non-equipartition
• Global magnetohydrodynamic simulations of the inner regions of protoplanetary discs. I. Zero-net flux regime
• Dust Drift Timescales in Protoplanetary Disks at the Cusp of Gravitational Instability
• Molecules with ALMA at Planet-forming Scales (MAPS) XVII: Determining the 2D Thermal Structure of the HD 163296 Disk
• Inferring the Gas-to-Dust Ratio in the Main Planet-Forming Region of Disks