Spatial Profiles of 3I/ATLAS CN and Ni Outgassing from Keck/KCWI Integral Field Spectroscopy

Abstract

Abstract Cometary activity from interstellar objects provides a unique window into the environs of other stellar systems. We report blue-sensitive integral field unit (IFU) spectroscopy of the interstellar object 3I/ATLAS from the Keck II–mounted Keck Cosmic Web Imager on 2025 August 24 UT. We confirm the previously reported CN and Ni outgassing and, for the first time, present the radial profiles of Ni and CN emission in 3I/ATLAS. We find characteristic e -folding radii of 593.7 ± 14.8 km for Ni and 841.0 ± 15.4 km for CN; this suggests that the Ni emission is more centrally concentrated in the comet’s nucleus and favors hypotheses involving easily dissociated species, such as metal carbonyls or metal–polycyclic aromatic hydrocarbon (PAH) molecules. Additional integral field spectroscopy after perihelion will provide an ongoing opportunity to determine the evolution of the radial distributions of species in the interstellar comet 3I/ATLAS.