Glitters of Warm H₂ in the Cold Interstellar Medium

¹ LERMA, ENS & Observatoire de Paris, France
² IAS, Orsay, France
³ LERMA, Observatoire de Paris, France
⁴ IRAM, Grenoble, France

Abstract

We present the scientific case for a high resolution spectro-imager in the mid-IR that would be 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 in galaxies. 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 in galaxies, will be traced by the emission of glitters of warm H₂ heated, throughout the medium, by the dissipation of omnipresent turbulence. The main scientific objectives are to (i) directly measure the mass and temperature distribution of the warm H₂, far from star forming regions, in particular in low metallicity environments where the traditional 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 H₂ in a large sample of galaxies along the Hubble sequence.