Observational signatures of eccentric Jupiters inside gas cavities in protoplanetary discs

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. 2D hydrodynamical simulations are performed and post-processed by 3D radiative transfer calculations. In our disc model, the planet eccentricity reaches similar to 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 (CO)-C-12 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 (CO)-C-12 J=3 -> 2. The planet eccentricity does not, however, give rise to detectable signatures in (CO)-C-13 and (CO)-O-18 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(circle). 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.