Powerful outflow is considered as an important mechanism to quench star formation in massive galaxy. A luminous AGN is supposed to drive an outflow to high velocity (e.g., over 1000 km/s). Recently a sample of ULIRGs with extremely fast outflows (1000–2000 km/s) was reported. However, these ULIRGs only show AGN signatures in large scale, i.e., fast outflow and ionization cone, while the MIR radiation from pc-scale dusty torus is not detected. The combination of large scale AGN activity and non-detection of AGN in the central region suggests "fading AGNs" in the ULIRGs, and the observed extreme outflow could be relics of AGN activity in a past active episode, i.e., "fossil outflows". Although simulation works predict a significant population of those fossil outflows since outflows can persist much longer than the active episode of driving AGN, those observational identification is still rare in the literature. The proposal provides the largest sample of identified fossil outflows powered by past AGN activity, which is the first-ever opportunity for a statistical study. We propose FOCAS IFU observation to resolve the outflow structure, investigate AGN activity history, and quantitively determine its feedback effect on evolution of host galaxy.
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