Assembly of Galaxies
Galaxy interactions can trigger powerful episodes of star formation and also can activate accretion onto nuclear supermassive black holes, producing an AGN. In the initial stages, these processes are deeply shrouded in the interstellar medium of the colliding galaxies. This material obscures our view nearly completely in the optical and near infrared, and the activity is most easily studied through the strong reradiated emission and emission line spectra in the mid-infrared and accessible to MIRI.
For example, the black hole accretion sources produce hard ultraviolet fluxes that can be identified by high excitation mid-infrared fine structure lines. A key line is [NeVI] at 7.65mm rest wavelength; it is the shortest wavelength bright high excitation line (see Figure 3). In addition, its rest wavelength lies in a region of exceptional transparency of the interstellar medium, A7.6mm < 0.02 AV. Thus, sources where the rest optical line emission is totally inaccessible can be studied with this line using MIRI up to z ~ 2.5, determining key parameters such as the true AGN hard UV energetics.
Dusty luminous galaxies (Ivision et al. 2004) with submm 'MAMBO' survey galaxies detected by Spitzer