The Herschel Lensing Survey

For deep imaging longward of 100 um, confusion noise sets thefundamental sensitivity limits achievable with Herschel, and theselimits cannot be improved by integrating longer. As a result,Herschel PACS/SPIRE images will not quite reach the depth of Spitzer24 um, not to mention that of ALMA. This means that with the rawsensitivities of PACS and SPIRE, it will be difficult to reach thepopulation of infraredluminous galaxies at z>2. To penetrate throughthe Herschel confusion limits with the lensing power of massive galaxyclusters and to reach z>2 infraredluminous galaxies, we propose herea deep PACS/SPIRE imaging survey of 40 lensing clusters, which havecarefully been selected from the past and ongoing HST/Spitzersurveys. Although both the PACS and SPIRE GT teams will conductsimilar surveys, its small sample size of 10 clusters is not enough tofully achieve the great potential of such a survey since highlymagnified (e.g., >510x) lensed galaxies are rare. By expanding thesample size by a factor of four, and by preselecting most spectacularsources from our ongoing Spitzer 24um survey of virgul100 Xrayluminous(i.e., massive) clusters, we will detect a significant number ofhighly magnified infraredluminous galaxies at z>2 with PACS andSPIRE, which will enable us to (1) resolve a large fraction of thefarinfrared/submillimeter background in the PACS/SPIRE bands and (2)map out the full spectral energy distributions (SEDs) of detectedgalaxies from midinfrared to submillimter. Such an extensive survey oflensing clusters will be a great legacy of Herschel, providing a largenumber of interesting highredshift targets for ALMA followup in thefuture. Because of the large sample size and strong lensing power ofthe targeted clusters, this survey also offers a great potential forbreakthrough discoveries such as the first detection of a starforming(i.e., non truncated!, P [truncated!, Please see actual data for full text]