COSMOS is a scientific and instrumental program designed for the Gran Telescopio de Canarias (GTC), currently under construction by the Instituto de Astrofísica de Canarias (IAC) on La Palma. The main science driver is to characterize the galaxy population during the epoch of maximum star formation in the history of the universe. According to recent studies, this critical epoch occurred when the universe was 10-40% of its current age, which corresponds to redshifts 1 < z < 2 . At these redshifts, the optical window -the region of the spectrum that has been most widely studied in nearby galaxies- is shifted into the near infrared (1-2.5 microns). Major spectroscopic surveys down to 1.8 microns are currently being planned to study the rest-frame optical properties of galaxies and the global star formation of the universe at z up to 1. We propose to carry out a comprehensive study of galaxies at 2 < z < 3, including: morphology, structure, kinematics, stellar population, star formation rate, metallicity, luminosity and mass functions, clustering, and large scale-structure. The goal is to understand the nature of these distant galaxies and assess their role in the star formation history of the universe, by comparing directly their rest-frame optical properties with those of the nearby population. COSMOS will be the first major survey to extend these studies to the high-z universe.

To carry out this project, we propose to build EMIR (Espectrógrafo Multiobjeto Infrarrojo). EMIR is designed to provide both high-multiplex (100 simultaneous objects over a 6 arcmin diameter field) and integral-field spectroscopy, covering the 1-2.5 microns range with a resolution of 5000. EMIR will be indeed a unique instrument in its class, being the first multi-object spectrograph operating in the K-band, long before 2007 when a similar instrument is scheduled for Gemini. The estimated cost of designing, constructing, and commissioning EMIR is $4.5M.

The science team behind COSMOS includes a group of -mostly- Spanish astronomers, with experience in both the study of the nearby and distant universe, and the use of 10-m class telescopes similar to GTC. We propose EMIR be constructed by a consortium of foreign and Spanish institutions led by the IAC, including: Durham (UK), and OMP(France) which would offer their extensive expertise in instrumentation in addition to technical and human resources, and INTA and UCM (Spain), which would provide support with the electronics, hardware, and software. These institutions may also provide additional sources of funding.

In summary, COSMOS will provide a unique first-class instrument and an immediate outstanding scientific return for the GTC. Our program will also make excellent use of other observational facilities in La Palma. We emphasise that the construction of EMIR will benefit the entire Spanish astronomical community given its versatility to accomplish a wide variety of projects in stellar, galactic, and extra-galactic astronomy, and the opportunity it offers to develop our own expertise in instrumentation for 10m-class telescopes in collaboration with world-class experts. Indeed, the collective expertise gained in completing COSMOS will be key to build a solid instrumental and scientific foundation upon which Spanish participation in the new astronomy of the XXI century will be firmly anchored.