Observational signatures of eccentric Jupiters inside gas cavities in protoplanetary discs

TL;DR

This study uses hydrodynamical and radiative transfer simulations to identify observable signatures of an eccentric Jupiter-sized planet inside a protoplanetary disc cavity, aiding in unseen planet detection.

Contribution

It demonstrates how planet eccentricity influences gas asymmetries and velocity structures detectable with ALMA, providing new observational diagnostics for eccentric planets.

Findings

Eccentric Jupiter induces large-scale asymmetries in 12CO emission.

Eccentricity causes detectable distortions in velocity maps.

No significant signatures in dust or near-infrared scattered light.

Abstract

Predicting how a young planet shapes the gas and dust emission of its parent disc is key to constraining the presence of unseen planets in protoplanetary disc observations. We investigate the case of a 2 Jupiter mass planet that becomes eccentric after migrating into a low-density gas cavity in its parent disc. Two-dimensional hydrodynamical simulations are performed and post-processed by three-dimensional radiative transfer calculations. In our disc model, the planet eccentricity reaches ~0.25, which induces strong asymmetries in the gas density inside the cavity. These asymmetries are enhanced by photodissociation and form large-scale asymmetries in 12CO J=3-2 integrated intensity maps. They are shown to be detectable for an angular resolution and a noise level similar to those achieved in ALMA observations. Furthermore, the planet eccentricity renders the gas inside the cavity eccentric, which manifests as a narrowing, stretching and twisting of iso-velocity contours in velocity maps of 12CO J=3-2. The planet eccentricity does not, however, give rise to detectable signatures in 13CO and C18O J=3-2 inside the cavity because of low column densities. Outside the cavity, the gas maintains near-circular orbits, and the vertically extended optically thick CO emission displays a four-lobed pattern in integrated intensity maps for disc inclinations > 30 degrees. The lack of large and small dust inside the cavity in our model further implies that synthetic images of the continuum emission in the sub-millimetre, and of polarized scattered light in the near-infrared, do not show significant differences when the planet is eccentric or still circular inside the cavity.