Observability of forming planets and their circumplanetary discs - IV. With JWST and ELT

To understand the potential for observing forming planets and their circumplanetary discs (CPDs) with James Webb Space Telescope (JWST) and Extremely Large Telescope (ELT), we created mock observations from three-dimensional radiative hydrodynamic simulations and radiative transfer post-processing for planets with 10, 5, and 1 Jupiter and 1 Saturn masses with orbital separation of 50 and 30 au in 0, 30, and 60 degrees inclinations. Instrumental effects were then simulated with Mirage for JWST/NIRCam and NIRISS, MIRISim for JWST/MIRI, and SimCADO and SimMETIS for ELT/MICADO and METIS. We found that the longer wavelengths (mid-infrared and beyond) are the best to detect CPDs, since they allow CPD of planet with smaller mass to be detected. MIRI on JWST and METIS on ELT offer the best possibility on these telescopes. Specifically, below 3 mu m, only 10(Jup) planets with their CPDs are detectable with NIRCam and MICADO. 5 M-Jup planets are only detectable if at 30 au (i.e. closer) orbital separation. Planets above 5 Mj up with their CPDs are detectable between 3 and 5 mu m with NIRCam and METIS LIM band, or above 10 um with MIRI and METIS N band. For <= 1 M-Jup planets >15 mu m are needed, where MIRI uniquely offers imaging capability. We present magnitudes and spectral energy distributions for separate components of the planet + CPD + circumstellar disc (CSD) system, to differentiate the extinction rates of CPDs and CSDs and to provide predictions for observational proposals. Because the CPD turns out to be the main absorber of the planet's emission, especially <10 mu m, this makes the detection of forming planets quite challenging.