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SUMMARY:Planck and the Optical Depth to Reionization - George Efstathiou (
 IoA\, Cambridge)
DTSTART:20160602T150000Z
DTEND:20160602T160000Z
UID:TALK65682@talks.cam.ac.uk
CONTACT:Simon Hodgkin
DESCRIPTION:The inter-galactic medium at  redshifts less than about 7 is h
 ighly ionized. But when was it ionized? What can we learn about the first 
 sources of UV photons and the emergence of structure from the dark ages? O
 bservations of the cosmic microwave background can offer clues\, particula
 rly from measurements of large-angle polarization anisotropies. In this ta
 lk\, I will review the constraints on the  optical depth to reionization\,
  tau\,  from WMAP\, the Planck LFI (low frequency instrument) and HFI (hig
 h frequency instrument). Each of these provides a\nnear-independent measur
 ement of tau.  Control of systematic errors in these experiments is critic
 al\, but highly technical. I will  therefore try to give a non-technical a
 ccount suitable for non-specialists. By the end of  the talk\, I hope that
  people will have a feel for the issues involved and whether the recent Pl
 anck results indicating tau ~ 0.05 are reliable.\n
LOCATION:Sackler Lecture Theatre\, IoA (tea at 3:30 pm)
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