The Interstellar Gas Seen in the Mid- and Far-infrared: the Promise of Spica Space Telescope

The midand far-IR spectral ranges are critical windows to characterize the physical and chemical processes that transform the interstellar gas and dust into stars and planets. Sources in the earliest phases of star formation and in the latest stages of stellar evolution release most of their energy at these wavelengths. Besides, the midand far-IR ranges provide key spectral diagnostics of the gas chemistry (water, light hydrides, organic species ...), of the prevailing physical conditions (H2, atomic fine structure lines ...), and of the dust mineral and ice composition that can not be observed from ground-based telescopes. With the launch of JAXA’s SPICA telescope, uninterrupted studies in the midand far-IR will be possible since ESA’s Infrared Space Observatory (1995). In particular, SAFARI will provide full access to the ∼34-210μm waveband through several detector arrays and flexible observing modes (from broadband photometry to medium resolution spectroscopy with R∼3,000 at 63μm), and reaching very high line sensitivities (∼10 Wm, 5σ-1hr) within a large FOV (∼2×2). Compared to previous farIR instruments (ISO /LWS,Akari/FIS, Spitzer/MIPS and Herschel/PACS), SAFARI will provide a superior way to obtain fully-sampled spectro-images and continuous SEDs of very faint and extended ISM sources in a wavelength domain not accessible to JWST or ALMA. The much increased sensitivity of SPICA will allow us to step forward and reveal not only the chemical complexity in the local ISM, but also in the extragalactic ISM routinely.