GYES and 3D mapping of the galactic ISM
Lallement, R., Marshall D., Vergely J.L., Crifo F., Raimond S.
The need for realistic three-dimensional interstellar medium distributions in the Galaxy has strongly increased in the context of the new missions: -(i) the building of a 3D distribution of dust will be part of a whole self-consistent analysis of Gaia -(ii) the ISM structure is important in the context of the Planck and Fermi missions, because the interstellar radiation field (responsible for dust heating and emission) and the cosmic ray propagation and diffusion (that influences the gamma ray diffuse emission) both depend on the 3D distribution of gas and dust. -(iii) studies of stellar-interstellar interfaces now currently detected with new generation instruments from ground or space require the physical properties of the ambient ISM in each case. In addition, 3D maps can be of wide use: optimization of searches for faint objects, identification of foreground and background for specific objects, - multi-phase ISM structure and evolution etc Such maps can only be built based on ISM absorption lines or colour excesses measured towards stars of know distance, with absorption spectra having the advantage of additionally providing information on the kinematics and abundances. However they require time consuming high-resolution data. A solution to this problem is the use of a multi-fibre spectrograph, preferentially in association with a stellar survey. This is exactly what GYES would provide! We will detail existing methods and 3D maps, in particular nearby ISM maps from absorption data inversion, and discuss their potential extension to the galactic scale using GYES observations in support to Gaia.