Authors: M. Gruntman and V. Izmodenov

Title: Energetic Neutral Atoms as tracers of the ionization state of the Local Interstellar Medium


Global images of the heliosphere in energetic neutral atom (ENA) fluxes are a powerful tool to study the solar wind interaction with the surrounding local interstellar medium (LISM). We explore the sensitivity of the images to the ionization state of the LISM. Solar wind plasma is compressed and heated in the termination shock transition. The shocked solar plasma is convected toward the heliospheric tail in the heliosheath, the region between the termination shock and the heliopause. The ENAs that are produced in charge exchange of the heated plasma and background neutral gas can be readily detected at 1 AU. Global ENAs images, the angular and energy dependences of ENA fluxes, are essentially dependent on the solar plasma density, temperature, and velocity in the heliosheath. The size and structure of the heliospheric interface region depend on the parameters of the interstellar plasma and gas. Hence the ENA images would also depend on the LISM parameters. We explore in this work the sensitivity of the ENA images to the ionization state of the LISM. We use an axis-symmetric model of the solar wind/LISM interaction with the self-consistent treatment of plasma-gas coupling and Monte Carlo simulations of the neutral gas distribution.