HLS-snapshot I


The “SPIRE Snapshot Survey of Massive Galaxy Clusters” (PI: E Egami) is attempting to find a large number of extremely IR-bright galaxies by observing ~300 X-ray-selected massive clusters with short, shallow imaging at 250–500 μm. The great sensitivity and observing efficiency of Herschel/SPIRE makes such a large sample achievable in ~30 hours. The survey follows the ROSAT Millennium Cluster Sample, based on the ROSAT All-Sky Survey, which comprises 357 clusters with an X-ray luminosity brighter than 5×10^44 erg/s (0.1–2.4 keV). After screening for targets already selected for Herschel key programs, the SPIRE Snapshot Survey consists of 279 clusters distributed over the whole sky and in the redshift range z=0.1-0.5.

The main science goals of the survey are as follows:

  1. Search for exceptionally bright (> 200 mJy) lensed galaxies - These sources are rare, but will stand out immediately. Once identified, extensive follow-up will commence.

  2. Study faint SPIRE sources - The SPIRE maps detect sources down to ~50 mJy (5 sigma), which is comparable to the confusion limit (~30 mJy). We can therefore study a large number of < 200 mJy sources such as background lensed galaxies (e.g. Rex et al. 2010) and cluster members (e.g. Rawle et al. 2010). A conservative estimate based on the first 25 observations indicates that the survey will easily detect 4000 sources.

  3. Investigate the SZ signal - For the most luminous X-ray clusters, the SZ increment signal may be directly detectable (e.g. Zemcov et al. 2010). Combined with a stacking analysis of less-luminous clusters, we can examine whether the ICM gas temperature is high enough to produce relativistic electrons, which will distort the resultant SZ increment signal.

  4. Brightest cluster galaxies - It has long been suspected that there may be a link between IR-bright BCGs and the strong cool-core hosts. The SPIRE snapshot survey will provide a large unbiased sample of BCGs/hosts.



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