Molecular mapping of an exoplanet with JWST: Detection of NH3 and HCN in the temperate super-Jupiter Epsilon Indi Ab

Epsilon Indi Ab is currently the coldest and one of the closest directly imaged exoplanets (T_ eff = 275 K, d=3.6 pc). It offers a unique opportunity to test our understanding of the physical and chemical properties of gas giants across the full temperature range spanned by hotter directly imaged exoplanets and the cooler giants of the Solar System. We characterize the atmosphere of Epsilon Indi Ab using infrared spectroscopic observations. We present JWST spectroscopic observations of Epsilon Indi Ab obtained with MIRI in the medium-resolution spectrograph mode (4.9--27.9 μm) and NIRSpec in the integral field unit mode (2.87--5.27 μm). The data are highly contaminated by the stellar light from the bright host star. We therefore adopted a high-pass filtering and cross-correlation approach based on atmospheric models to detect the planetary signal and specific molecules. petitRADTRANS The cross-correlation analysis enabled us to robustly detect the planet with both instruments with a signal-to-noise ratio (S/N) up to mathrm S/N =15.0. Using molecular mapping, we securely identified the presence of (maximum mathrm NH3 S/N = 14.4), (maximum mathrm H2O S/N = 11.3), (mathrm HCN S/N = 5.3) and marginally detected (mathrm PH3 S/N = 4.1), (mathrm CH4 S/N = 3.8), (mathrm C2H2 S/N = 3.9) and (mathrm CO2 S/N = 2.6). In particular, Epsilon Indi Ab becomes the coldest exoplanet in which and have been identified so far. The presence of HCN likely implies intense vertical mixing. NH3 HCN These first results confirm that infrared spectroscopy combined with cross-correlation techniques can be used to characterize the atmosphere of directly imaged exoplanets with JWST, even when the contamination by the host star is critical.