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arXiv 1205.2697astro-ph.CO
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吸收中的大尺度结构:星系空洞内和周围的气体

Large Scale Structure in Absorption: Gas within and around Galaxy Voids

Nicolas Tejos, Simon L. Morris, Neil H. M. Crighton, Tom Theuns, Gabriel Altay, Charles W. Finn

摘要:

我们调查的HI Ly-a吸收系统(Ly-a森林)内和周围的星系空洞在z <0.1的属性。我们发现显著过量(> 99%c.l.)在~5 h ^{-1} Mpc尺度上,Ly-a系统在星系空洞边缘的随机分布。我们没有发现显着的差异,在内部空洞的随机期望系统的数量。我们报告了在> 98%和> 90%c.l.星系空洞内部和边缘发现的Ly-a系统的柱密度(N_{HI})和多普勒参数(b_{HI})分布之间的差异。分别低密度环境(空隙)的N_{HI}和b_{HI}值均小于高密度环境(空隙边缘)的值。这些趋势在理论上是预期的,也发现在GIMIC,一个国家的最先进的流体动力学模拟。我们的发现与至少三种类型的Ly-alpha的情况是一致的:(1)包含嵌入星系,因此与星系直接相关(称为“晕状”),(2)与星系相关,只是因为它们位于同一个过密LSS中,以及(3)与低密度LSS相关,具有非常低的自相关幅度(~随机),与发光星系无关。我们认为,后者出现在结构仍然线性增长的原始密度波动内的星系空洞,还没有形成星系,因为它们的低密度。我们估计,这些低密度LSS吸收体占当前Ly-a群体(N_{HI}> 10 ^{12.5} cm ^{-2})的25 - 30% ± 6%,而其他两种类型占剩余的70 - 75% ± 12%。假设只有N_{HI}> 10 ^{14} cm ^{-2}的系统附近有嵌入星系,我们估计"类晕" Ly-a的贡献约为12 - 15% ± 4%,因此约55 - 60% ± 13%的Ly-a系统与过密的LSS有关。

英文摘要:

We investigate the properties of the HI Ly-a absorption systems (Ly-a forest) within and around galaxy voids at z<0.1. We find a significant excess (>99% c.l.) of Ly-a systems at the edges of galaxy voids with respect to a random distribution, on ~5 h^{-1} Mpc scales. We find no significant difference in the number of systems inside voids with respect to the random expectation. We report differences between both column density (N_{HI}) and Doppler parameter (b_{HI}) distributions of Ly-a systems found inside and at the edge of galaxy voids at the >98% and >90% c.l. respectively. Low density environments (voids) have smaller values for both N_{HI} and b_{HI} than higher density ones (edges of voids). These trends are theoretically expected and also found in GIMIC, a state-of-the-art hydrodynamical simulation. Our findings are consistent with a scenario of at least three types of Ly-alpha: (1) containing embedded galaxies and so directly correlated with galaxies (referred as `halo-like'), (2) correlated with galaxies only because they lie in the same over-dense LSS, and (3) associated with under-dense LSS with a very low auto-correlation amplitude (~ random) that are not correlated with luminous galaxies. We argue the latter arise in structures still growing linearly from the primordial density fluctuations inside galaxy voids that have not formed galaxies because of their low densities. We estimate that these under-dense LSS absorbers account for 25-30% +- 6% of the current Ly-a population (N_{HI} > 10^{12.5} cm^{-2}) while the other two types account for the remaining 70-75% +- 12%. Assuming that only N_{HI} > 10^{14} cm^{-2} systems have embedded galaxies nearby, we have estimated the contribution of the `halo-like' Ly-a to be ~12-15% +- 4% and consequently ~55-60% +- 13% of the Ly-a systems to be associated with the over-dense LSS.

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