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[2013-11-5]: SZ effect or Not? - Detecting most galaxy clusters’ main foreground effect
2013-10-29  |  作者:  |  【  】 【打印】 【关闭

  [Seminar]

  ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

  Title: SZ effect or Not? - Detecting most galaxy clusters’ main foreground effect

  Speaker: Dr. Weike Xiao

  Affiliation: Department of Astrophysics and Applied physics, Harbin Institute of Technology

  Time:  Nov 5, 2013 (Tuesday) 9:30 a.m.

  Venue: Meeting Room 401 (Main Building)

  Abstract:

  Galaxy clusters are the most massive objects in the Universe and comprise a high-

  temperature intracluster medium of about 107 K, believed to offer a main foreground

  effect for cosmic microwave background (CMB) data in the form of the thermal

  Sunyaev-Zeldovich (SZ) effect. This assumption has been confirmed by SZ signal

  detection in hundreds of clusters but, in comparison with the huge numbers of clusters

  within optically selected samples from Sloan Digital Sky Survey (SDSS) data, this only

  accounts for a few percent of clusters. Here we introduce a model-independent new

  method to confirm the assumption that most galaxy clusters can offer the thermal SZ

  signal as their main foreground effect. For the Wilkinson Microwave Anisotropy Probe

  (WMAP) seven-year data (and a given galaxy cluster sample), we introduced a parameter

  d1 as the nearest-neighbour cluster angular distance of each pixel, then we

  classified data pixels as to be (d1!0 case) or not to be (d1 large enough) affected by

  the sample clusters. By comparing the statistical results of these two kinds of pixels, we

  can see how the sample clusters affect the CMB data directly. We find that the Planck

  Early Sunyaev-Zeldovich (ESZ) sample and X-ray samples (102 clusters) can lead to

  obvious temperature depression in the WMAP seven-year data, which confirms the

  SZ effect prediction. However, each optically selected sample (> 104 clusters) shows

  an opposite result: the mean temperature rises to about 10μ K. This unexpected

  qualitative scenario implies that the main foreground effect of most clusters is not

  always the expected SZ effect. This may be the reason why the SZ signal detection result

  is lower than expected from the model.

  ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

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       南方天文观测基地

  中国科学院天体结构与演化重点实验室

  云南天文台学术委员会

  2013-10-29

 
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