Glitters of Warm H₂ in the Cold Interstellar Medium

Abstract

We present the scientific case for a high resolution spectro-imagerin the mid-IR that wouldbe dedicated to the mapping of H₂ emission in its four lowest rotational transitions, at 28.2, 17.0, 12.3 and 9.7 micron with a spectral resolution ~10⁴ sufficient to provide kinematical distances ingalaxies. The proposed instrument on a 2 m-class telescope will be most sensitive to H₂ line emission simultaneously extended and structured at small scale, in gas at temperatures higher than 80 K. Colder H₂,which may contribute most of the baryonic dark matter ingalaxies, will be traced by the emission of glitters of warm H₂heated, throughout the medium, by the dissipation of omnipresent turbulence.The main scientific objectives are to (i) directly measure themass and temperature distribution of the warm H₂, far from star formingregions, in particular in low metallicity environments where thetraditional tracers of H₂ (CO, dust emission) fail, (ii) trace the dissipation of turbulence in the perspective of building a global view of the star formation process in galaxies and (iii)trace baryonic dark matter in the form of cold H₂in a large sample of galaxies along the Hubble sequence.