| Description |
For deep imaging longward of 100 um, confusion noise sets thefundamental sensitivity limits achievable with Herschel, and theselimits cannot be improved by integrating longer. To penetrate throughthis confusion limit and detect faint high-redshift galaxies,gravitational lensing by massive galaxy clusters offers a verypowerful and yet cheap solution. For this reason, we are currentlyconducting a PACS/SPIRE imaging survey of virgul40 massive lensing clustersas one of the Herschel Key Programs, The Herschel Lensing Survey(PI: Egami, 292.3 hrs). Although this program is producing manyexciting results as reported in our 5 Herschel special-issue papers,one thing is becoming clear: it is extremely difficult to find lensedgalaxies that are bright enough (> 200 mJy in SPIRE bands) to performspectroscopy with PACS/SPIRE. This disappointment, however, wasquickly overcome by the serendipitous discovery of an exceptionallybright (virgul500 mJy@350 um) z=2.3 galaxy lensed by a massive cluster atz=0.325. This discovery suggests that if we survey a large enoughcluster sample, we will find similarly bright lensed sources that makeall kinds of exciting follow-up observations possible. Here, wepropose to conduct such a survey by taking advantage of the MillenniumCluster Sample constructed from the ROSAT All-Sky Survey with manyyears of extensive follow-ups. More specifically, we will conduct aSPIRE snapshot survey of 279 X-ray-selected clusters. SPIRE.s greatsensitivity and observing efficiency means that we can complete thisprogram in only 27 hours while achieving a nearly confusion-limitedsensitivity of 10 mJy (1 sigma). Such a depth will allow all kinds ofsecondary science projects as well. Although SPIRE wide-area surveyslike H-ATLAS will also discover many bright lensed galaxies, thesesources are mostly lensed by galaxies and not clusters, which makesour approach an economic alternative to investigate a different typeof lensed systems. |
