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Chandra measurements of a complete sample of x-ray luminous clusters: The gas mass fraction.

机译：X射线发光簇的完整样品的Chandra测量：气体质量分数。

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摘要

Clusters of galaxies are the largest known bound systems in the Universe and are formed from the collapse of primordial density fluctuations. Since clusters are extremely large and massive, the cluster's baryons and dark matter originated from approximately the same comoving volume, and thus it is believed that their ratio should be representative of the Universe. Current studies indicate that the cluster baryon fraction is lower than the cosmic baryon fraction as measured by the Omegab / OmegaM parameter.;To address this issue, the gas mass fraction, ƒgas, is measured out to large radii for a complete sample of the 35 most luminous clusters from the Brightest Cluster Sample and its extension at redshifts z = 0.15 -- 0.30 using Chandra X-ray data. This sample includes relaxed and unrelaxed clusters, and the data were analyzed using two different models for the gas density and temperature of the cluster. In accord with earlier studies, the gas mass fraction is shown to increase with radius, and thus the value of ƒgas depends on the radius used. However, the background of the surface brightness and temperature profiles often limits the radius out to which masses can be measured accurately. Therefore, measurements for the entire sample were limited to r500, the radius within which the mass density is 500 times the critical density. The average gas mass fraction for this sample of clusters at r500 is measured to be ƒ gas = 0.163 +/- 0.032, which is in agreement with the cosmic baryon fraction (Omegab / OmegaM = 0.167 +/- 0.006) at the 1sigma level, after adding the stellar baryon fraction. In this analysis, it is shown that the most X-ray luminous clusters in the redshift range z = 0.15 -- 0.30 have a gas mass fraction that is consistent with the cosmic value at r500.
机译：星系团是宇宙中最大的已知系统，是由原始密度波动的崩溃形成的。由于星团非常大且巨大，所以星团的重子和暗物质起源于大致相同的共同运动体积，因此可以认为它们的比率应代表宇宙。当前的研究表明，通过Omegab / OmegaM参数测得的簇重子分数低于宇宙重子分数。为了解决这个问题，对35个完整样本的气体质量分数ƒgas进行了大半径测量使用钱德拉X射线数据，从最亮簇样本中提取的大多数发光簇及其在红移z = 0.15-0.30处的扩展。该样本包括松弛和无松弛的星团，并使用两种不同的模型对星团的气体密度和温度进行了数据分析。与早期的研究一致，气体质量分数显示为随半径增加，因此ƒgas的值取决于所使用的半径。但是，表面亮度和温度曲线的背景通常会限制可精确测量质量的半径。因此，整个样品的测量值限制为r500，即半径范围内的质量密度是临界密度的500倍。该团簇样品在r500的平均气体质量分数经测量为ƒgas = 0.163 +/- 0.032，这与1sigma水平的宇宙重子分数（Omegab / OmegaM = 0.167 +/- 0.006）相符，加入恒星重子部分后。在此分析中，显示出在红移范围z = 0.15-0.30中的大多数X射线发光簇具有与r500的宇宙值一致的气体质量分数。

著录项

  • 作者

    Landry, David.;

  • 作者单位

    The University of Alabama in Huntsville.;

  • 授予单位 The University of Alabama in Huntsville.;
  • 学科 Physics Astrophysics.;Physics Astronomy and Astrophysics.
  • 学位 Ph.D.
  • 年度 2013
  • 页码 204 p.
  • 总页数 204
  • 原文格式 PDF
  • 正文语种 eng
  • 中图分类 TS97-4;
  • 关键词

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