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The combination of surveys at different wavelengths, from ISOCAM, ISOPHOT and SCUBA, together with the the shape and intensity of the CIRB, was used by several authors to constrain the parameters of their backward evolution models assuming a combination of luminosity and density evolution as a function of redshift of the IR luminosity function at 15 or 60 µm : Roche & Eales (1999), Tan et al. (1999), Devriendt & Guiderdoni (2000), Dole et al. (2000), Chary & Elbaz (2001), Franceschini et al. (2001, 2003), Malkan & Stecker (2001), Pearson (2001), Rowan-Robinson (2001), King & Rowan-Robinson (2003), Takeuchi et al. (2001), Xu et al. (2001, 2003), Balland et al. (2003), Lagache, Dole & Puget (2003), Totani & Takeuchi (2002), Wang (2002).

Being limited by the sensitivity of the extragalactic surveys, the major output of these models was to show that LIRGs and ULIRGs were much more common in the past than they are today. Chary & Elbaz (2001) derived that the comoving IR luminosity due to LIRGs was about seventy times larger at z ~ 1 than it is today (Fig. 15). Quite logically, it resulted that the contribution of LIRGs to the cosmic star formation history was so large in the past that it dominated the integrated star formation that galaxies experienced in the past. Hence, LIRGs should now be considered not as a type of galaxies but instead as a common phase of intense star formation that any galaxy may have experienced.

Figure 15

Figure 15. Star Formation Rate from Chary & Elbaz (2001). Upper panel: min and max range from their model, and observed UV/opt data; dots represent Xu et al. (2001) model. Lower panel: 3 different evolution scenarios from their model and data corrected for extinction. Line: pure luminosity; upper dash: pure density; lower dash: luminosity+density.

Elbaz et al. (2002) derived the contribution to the peak of the CIRB at 140 µm from the population of LIRGs around z ~ 0.8 detected in the ISOCAM 15 µm deep surveys and found that these objects alone can explain more than two thirds of the peak and integrated intensities of the CIRB (see Fig. 16). Hence the CIRB is the signature of the strong redshift evolution of LIRGs and the fossil record of star formation which took place in such burst phases.

Figure 16

Figure 16. Integrated Galaxy Light (IGL, filled dots) and Extragalactic Background Light (EBL, open squares, grey area) from the UV to sub-millimeter (from Elbaz et al. 2002). EBL measurements from COBE: 200-1500 µm EBL from COBE-FIRAS (grey area, Lagache et al. 1999), 1.25, 2.2, 3.5, 100, 140 µm EBL from COBE-DIRBE (open squares). IGL in the U,B,V,I,J,H,K bands from Madau & Pozzetti (2000). The upper end of the arrows indicate the revised values suggested by Bernstein et al. (2001, factor two higher). 6.75 µm (ISOCAM-LW2 filter) IGL from Metcalfe et al. (2003, filled dot with error bar and arrow). Hatched upper limit from Mkn 501 (Stanev & Franceschini 1998). The ISOCAM 15 µm IGL (2.4 ± 0.5 nW m-2 sr-1) is marked with a star surrounded by a circle. The other star surrounded by a circle is the prediction of the contribution of the 15 µm sources to 140 µm (Elbaz et al. 2002).

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