Investigating the Relative Gas and Small Dust Grain Surface Heights in Protoplanetary Disks

Abstract

Dust evolution in protoplanetary disks from small dust grains to pebbles is key to the planet formation process. The gas in protoplanetary disks should influence the vertical distribution of small dust grains (∼1 μm) in the disk. Utilizing archival near-infrared polarized light and millimeter observations, we can measure the scale height and flare parameter β of the small dust grain scattering surface and 12CO gas emission surface for three protoplanetary disks: IM Lup, HD 163296, and HD 97048 (CU Cha). For two systems, IM Lup and HD 163296, the 12CO gas and small dust grains at small radii from the star have similar heights, but at larger radii (>100 au), the dust grain scattering surface height is lower than the 12CO gas emission surface height. In the case of HD 97048, the small dust grain scattering surface has similar heights to the 12CO gas emission surface at all radii. We ran a protoplanetary disk radiative transfer model of a generic protoplanetary disk with TORUS and showed that there is no difference between the observed scattering surface and 12CO emission surface. We also performed analytical modeling of the system and found that gas-to-dust ratios larger than 100 could explain the observed difference in IM Lup and HD 163296. This is the first direct comparison of observations of gas and small dust grain height distribution in protoplanetary disks. Future observations of gas emission and near-infrared scattered-light instruments are needed to look for similar trends in other protoplanetary disks.

Molecules with ALMA at Planet-forming Scales (MAPS) IV: Emission Surfaces and Vertical Distribution of Molecules

“…et al (2018) were the first to demonstrate an approach to directly extract CO emission surfaces in moderate resolution observations of IM Lup. Similar methods were then used by Teague et al (2018aTeague et al ( ,b, 2019 and Rich et al (2021) to constrain the emitting layers in AS 209 and HD 163296. Below, we compare these previous results to the high spatial resolution MAPS observations and comment on the relatively consistency and any salient differences.…”

“…2 are consistent, suggesting that the results presented here are not underestimated due to insufficient angular resolutions. Rich et al (2021) fit the CO 2-1 emission surfaces in the IM Lup disk using the DSHARP datacubes (Andrews et al 2018) with a similar extraction method. These images have a spatial resolution of ∼0.…”

CO Line Emission Surfaces and Vertical Structure in Midinclination Protoplanetary Disks

“…However, with the high angular resolution and surface brightness sensitivity provided by the Atacama Large Millimeter/submillimeter Array (ALMA), it is possible to extract disk vertical structures from midinclination (≈30°-75°) disks by exploiting spatially resolved emission from elevated regions above and below the midplane (e.g., de Gregorio-Monsalvo et al 2013;Rosenfeld et al 2013;Isella et al 2018). In these cases, the emission heights of bright molecular lines can be directly determined (Pinte et al 2018;Rich et al 2021;Paneque-Carreño et al 2021;Law et al 2021a). This approach expands the sample of disks whose vertical structure can be mapped and allows us to relate vertical gas structure to that of the radial continuum, which is often inaccessible in edge-on disks due to high optical depths.…”

Scattering and sublimation: a multi-scale view of $μ$m-sized dust in the inclined disc of HD 145718

“…Thus, probing the vertical disc structure allows us to probe the properties of the dust content of the disc. In recent years, observational constraints on the degree of flaring in the surface layers of dusty and gaseous components of protoplanetary discs have begun to be made (Ginski et al 2016;Avenhaus et al 2018;Pinte et al 2018;Villenave et al 2020;Rich et al 2021). Elliptical models, similar to those we employ in Section 4, have been used to determine the height of the scattering surface in concentric ring features of discs exhibiting substructure, with power law profiles (Equation ( 7)) then used to constrain the flaring exponent of the scattering surface, 𝛽 scat .…”