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Detecting the First Objects in the Mid-IR with NGST

We calculate the expected Mid-IR molecular hydrogen line emission from the first objects in the universe. Due to their low masses, the stellar feedback from massive stars is able to blowaway their gas content and collect it into a cooling shell where H_2 rapidly forms and IR roto-vibrational (as for example the restframe 2.12 micron) lines carry away a large fraction (up to 10%) of the explosion energy. The fluxes from these sources are in the range 10^{-21}-10^{-17} erg/s/cm^2. The highest number counts are expected in the 20 micron band, where about 10^5 sources/deg^2 are predicted at the limiting flux of 3 \times 10^{-18} erg/s/cm^2. Among the planned observational facilities, we find that the best detection perspectives are offered by NGST, which should be able to reveal about 200 first objects in one hour observation time at its limiting flux in the above band. Therefore, Mid-IR instruments appear to represent perfect tools to trace star formation and stellar feedback in the high (z>5) redshift universe.