Abstract　 　　  

　I present an Herschel and Spitzer study on the ULIRGs at z~2. One of the great heritages of the Spitzer Space Telescope is detection of PAH emission from star forming galaxies. The strong PAH emission at rest 7.7\,$\mu$m provides not only a good measure of star formation rate but also a good photometric redshift estimate.  A PAH-selected star forming galaxy sample will have better-determined photometric redshifts than a FIR selected sample.   Neither sample suffers much bias because of dust attenuation, and thus the PAH-selected sample provides a fair estimate of the star forming population at any redshift. The Spitzer IRAC 8\,$\mu$m, the IRS peak-up 16\,$\mu$m, and the MIPS 24\,$\mu$m surveys effectively detect star forming galaxies with strong PAH emission at z=0, 1, and 2 respectively.  However, Spitzer 70 and 160\,\micron\ data are not sensitive enough to detect the FIR emission from most galaxies at high redshift.  Herschel PACS and SPIRE, which are sensitive enough to detect galaxies as far as $z>6$ will provide the needed data.  The combination of Spitzer and Herschel data will all measurement of the  star formation history from $z=2$ to the present.