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arXiv 0705.3289astro-phastro-ph.COastro-ph.HEastro-ph.IM
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星系团的氦丰度与Sunyaev-Zeldovich效应

Helium abundance in galaxy clusters and Sunyaev-Zeldovich effect

Maxim Markevitch

摘要:

长期以来,人们一直认为团内等离子体中的氦核可以很好地沉积在团引力势中。一些对松弛星系团核心的理论估计预测,氦丰度比其原始值高出几倍。星系团内的氦丰度无法直接测量。这为基于X射线导出的星系团数量(如气体质量、总质量和气体质量分数)的宇宙学测试提供了一个重要的不确定性来源,所有这些都取决于假设的氦丰度。我们指出,通过结合Sunyaev-Zeldovich(SZ)和X射线数据得出的集群距离也取决于氦丰度。这种依赖性可以用来测量丰度,只要距离是独立已知的。例如,如果采用WMAP的H_0值,那么Bonamente和他的合作者最近的H_0测量值,根据38个假设原始氦丰度的星团的SZ数据,对应于在r~1 Mpc内丰度过剩1.9 ± 0.8倍(仅使用他们的统计误差)。这表明,有趣的准确性是触手可及的。我们还简要地讨论了如何将SZ和X射线星系团数据结合起来解决d_a(z)宇宙学检验中氦丰度的依赖性。

英文摘要:

It has long been suggested that helium nuclei in the intracluster plasma can sediment in the cluster gravitational potential well. Some theoretical estimates for the cores of relaxed clusters predict an excess of helium abundance by up to a factor of a few over its primordial value. The intracluster helium abundance cannot be measured directly. This presents a significant source of uncertainty for cosmological tests based on the X-ray derived cluster quantities, such as the gas mass, total mass, and gas mass fraction, all of which depend on the assumed helium abundance. We point out that cluster distances derived by combining the Sunyaev-Zeldovich (SZ) and X-ray data also depend on the helium abundance. This dependence can be used to measure the abundance, provided the distance is known independently. For example, if one adopts the WMAP H_0 value, then the recent H_0 measurement by Bonamente and collaborators, derived from SZ data on 38 clusters assuming a primordial helium abundance, corresponds to an abundance excess by a factor of 1.9+-0.8 within r~1 Mpc (using only their statistical errors). This shows that interesting accuracy is within reach. We also briefly discuss how the SZ and X-ray cluster data can be combined to resolve the helium abundance dependence for the d_a(z) cosmological test.

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