The discovery of the Cosmic Infrared Background (CIB) in 1996, together with recent cosmological surveys from the mid-infrared (MIR) to the millimeter has revolutionized our view of star formation at high redshifts. It has become clear, in the last decade, that a population of galaxies that radiate most of their power in the far-infrared ("infrared galaxies") contributes a large part of the whole galaxy build-up in the Universe. Since the discovery of the CIB, new results on the identification of the sources contributing to the CIB, their redshift distribution, and their nature, are coming out at increasing speed, especially through multi-wavelength analysis. We are now in the position to migrate from an exploratory research to a deep understanding of this population. Our team has played a crucial role in the exploratory phase (e.g. discovery of the CIB, ISO deep surveys, participation to the discovery of submm galaxies) and we now want to take an active part in the complete characterization of this galaxy population. The present project aims at reinforcing our team, mostly by widening our expertise at other wavelengths and adding resources to our project by hiring 3 postdocs (see the announcement below).

Infrared galaxies show extremely high rates of evolution with redshift, exceeding those measured for galaxies at all other wavelengths and comparable to or larger than the evolution rates observed for quasars. For instance, the infrared comoving luminosity density was ~15 times larger at z~1 than in the local Universe ; for comparison, the far-ultraviolet luminosity density was only ~4 times larger at z=1 than today. The very strong evolution is driven by the evolution of the IR-bright galaxies, Luminous and Ultraluminous infrared Galaxies (LIRGs and ULIRGs) with luminosities 1112, respectively. Infrared luminosity function evolution is such that the power output is dominated by LIRGs at z~0.7-1.5 and ULIRGs at z~2-3. Understanding what processes are generating these enormous infrared luminosity outputs at high redshift is one of the challenges of the coming decade. The proposed project wants to address the most exciting and challenging questions in this field of research. Our immediate scientific objectives are to understand:
- The role of LIRGs and ULIRGs in the context of general galaxy population, their role in the mass assembly and their link to other high redshift galaxies.
- The physical properties of LIRGs and ULIRGs and their contribution to the CIB.
- The role of the small scale (merging, flyby) and large scale (nodes, filaments and sheets of the large-scale structures) environment on star formation.

The unique strength of our team will be to combine multi-wavelength imaging of wide and deep fields including MIPS/Spitzer and Akari infrared data with deep spectroscopy, including MIR IRS/Spitzer. The imaging component allows us to select large samples of LIRGs and ULIRGs at various redshifts and perform a fine statistical analysis in order to shed light on the relations between the starburst phenomenon and the general galaxy population, their respective evolution and impact through large-scale structures. The spectroscopic component allows us to gain a deeper insight into the physical processes at work in the LIRG and ULIRG phases. By nature, these samples are smaller, but this is compensated by the wealth of information gained on these objects. We will maintain a good control on the selection biases of our samples so that we can use the results of spectroscopic studies for the interpretation of imaging data and vice-versa.
More specifically, we will use the Spitzer and Akari data, in combination with GALEX, HST and ground based observations to understand i) the role of interactions in trigerring the LIRG and ULIRG phases at high redshift, ii) the quenching of star formation in the densest environments, iii) the localization of the star-formation in the cosmic web as a function of redshift. We will further characterize the link between LIRGs and ULIRGs and Lyman-Break Galaxies that are the largest sample of spectroscopically confirmed UV-selected high-redshift star-forming galaxies. With MIR Spitzer spectroscopy, we will disentangle the Active Galactic Nuclei/Starburst contribution to mid-IR emission, thus constrain the estimate of bolometric luminosities. Our spectra, in combination with brighter samples from previous Spitzer surveys, will allow us to trace the evolution of the strength of PAH emission and mid-IR opacities as a function of L(IR) and z. This evolution will be related to other physical properties such as morphology, metallicity and mass. Finally, our project will yield the fraction of the comoving bolometric luminosity density at z~0.5-3 arising from accretion and nucleosynthesis, one of the key goals of galaxy evolution studies.
Our project will rally our unique expertises and will strengthen our competitivity in the context of the future European Herschel mission.

The complete scientific case of the project can be found here [pdf].