Massive elliptical galaxies form through a two-phase process: an intense and fast star formation episode creates red, compact and massive objects (“red nuggets”), and then a second phase, dominated by mergers and gas inflows, causes structural evolution and size growth. 

Given the stochastic nature of mergers, a small fraction of red nuggets should survive, without experiencing any interaction, massive (M>8x10^11 solar masses) and compact (R<2kpc) until today: Relic Galaxies. This fraction highly depends on the processes dominating the size growth and how they are modeled. Thus, counting relics at low-z is an incredibly valuable way to disentangle between different galaxy evolution models. 

Relics are made of only “in situ” stars since they missed the “accretion” channels of size growth. As such, they provide a unique opportunity to track the evolution of this stellar component, which is mixed with the accreted one in normal galaxies. They are the only systems that allow us to understand the mass assembly in the early Universe with the amount of details currently available only in the local Universe. 

The goal of INSPIRE is building the first statistically large catalog of spectroscopically confirmed relics, thanks to an approved X-Shooter ESO Large Program, and comparing their number density with predictions from simulations.