Tracing the assembly history of galaxies over cosmic time remains a primary goal for observational and theoretical studies of the Universe. In recent years, large spectroscopic surveys at optical wavelengths (0.3 μm – 1 μm) have provided important information on the formation and evolution of galaxies, but near-IR spectroscopy is now required to extend our knowledge beyond z∼1. In fact, at these redshifts almost all the main spectral features used to determine the physical, chemical and dynamical properties of galaxies are shifted to λ > 1μm (e.g. Hα, OIII, Ca HK).
Exploiting the large multiplex and wavelength coverage of MOONS will provide high-quality spectra for a statistically significant number of galaxies (∼1 M) at z>1 for the first time, matching a similar rest-frame wavelength, volume, range of environments and stellar masses as the successful Sloan Digital Sky Survey (SDSS) in the local Universe. This will provide an unparalleled resource to study the physical processes that shape galaxy evolution and will determine the key relations between stellar mass, star-formation, metallicity and the role of feedback. Moreover, MOONS will fill a critical gap in discovery space, unveiling the redshift desert (1.5 < z < 3), enabling studies of this crucial epoch around the peak of star formation, the assembly of the most massive galaxies, the effects of environment on galaxy properties, and the connection with the growth of super-massive black holes.