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SUMMARY:Galaxy clusters at sub-millimeter wavelengths - Gianfranco De Zott
 i (Padua Observatory - INAF)
DTSTART:20170428T103000Z
DTEND:20170428T113000Z
UID:TALK71739@talks.cam.ac.uk
CONTACT:Martin Haehnelt
DESCRIPTION:The standard techniques for detecting galaxy clusters (optical
 /near-IR "red sequence"\, X-ray emission\, SZ effect) preferentially or ex
 clusively select evolved objects\, with mature galaxy populations and a ho
 t intra-cluster medium. As a result\, most known clusters are at redshifts
  <1.5\, i.e. below that of the peak of global star-formation activity. A c
 omplementary high-z cluster detection technique is to look for regions of 
 exceptionally high star-formation at far-IR/sub-mm wavelengths. Due to the
  low density of such objects on the sky\, large areas must be probed in or
 der to find a significant sample. This has motivated searches of (proto)-c
 luster candidates in the all-sky sub-mm maps produced by the Planck satell
 ite. \n\nThe Planck Collaboration has recently published a catalogue of mo
 re than two thousands sources with cold sub-mm colours\, suggestive of z>2
 \, over about 26% of the sky\, at high Galactic latitudes. Follow-up Hersc
 hel observations of a sub-sample of these sources have shown that almost a
 ll of them are highly significant overdensities of star-forming galaxies\,
  supporting their classification as galaxy (proto)-clusters. However\, we 
 have found that the number densities (or the flux-densities) of these obje
 cts are  far in excess of the expectations from the standard scenario for 
 the evolution of large-scale structure. Our simulations\, based on a physi
 cally motivated galaxy evolution model\, show that essentially all cold pe
 aks brighter than S(545GHz) = 500 mJy found in Planck maps after having re
 moved the Galactic dust emission can be interpreted not as individual (pro
 to)-clusters but as positive Poisson fluctuations of the number of high-z 
 overdensities of dusty galaxies within the Planck beam. The simulations ac
 curately reproduce the statistic of the Planck detections. Also the distri
 butions of sizes and ellipticities are in qualitative agreement with obser
 vations. The redshift distribution of the brightest proto-clusters contrib
 uting to the cold peaks has a broad maximum at 1.5 < z < 3. Perspectives f
 or sub-mm (proto)-cluster surveys are discussed.\n
LOCATION:Sackler Lecture Theatre\, IoA
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