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外文期刊>The Astrophysical journal
>CONSTRAINING CLUSTER PHYSICS WITH THE SHAPE OF X-RAY CLUSTERS: COMPARISON OF LOCAL X-RAY CLUSTERS VERSUS ΛCDM CLUSTERS
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CONSTRAINING CLUSTER PHYSICS WITH THE SHAPE OF X-RAY CLUSTERS: COMPARISON OF LOCAL X-RAY CLUSTERS VERSUS ΛCDM CLUSTERS
Recent simulations of cluster formation have demonstrated that condensation of baryons into central galaxies during cluster formation can drive the shape of the gas distribution in galaxy clusters significantly rounder out to their virial radius. These simulations generally predict stellar fractions within cluster virial radii that are ~2-3 times larger than the stellar masses deduced from observations. In this paper, we compare ellipticity profiles of simulated clusters performed with varying input physics (radiative cooling, star formation, and supernova feedback) to the cluster ellipticity profiles derived from Chandra and ROSAT observations, in an effort to constrain the fraction of gas that cools and condenses into the central galaxies within clusters. We find that local relaxed clusters have an average ellipticity of = 0.18 ± 0.05 in the radial range of 0.04 ≤ r/r 500 ≤ 1. At larger radii r 0.1r 500, the observed ellipticity profiles agree well with the predictions of non-radiative simulations. In contrast, the ellipticity profiles of simulated clusters that include dissipative gas physics deviate significantly from the observed ellipticity profiles at all radii. The dissipative simulations overpredict (underpredict) ellipticity in the inner (outer) regions of galaxy clusters. By comparing simulations with and without dissipative gas physics, we show that gas cooling causes the gas distribution to be more oblate in the central regions, but makes the outer gas distribution more spherical. We find that late-time gas cooling and star formation are responsible for the significantly oblate gas distributions in cluster cores, but the gas shapes outside of cluster cores are set primarily by baryon dissipation at high redshift (z ≥ 2). Our results indicate that the shapes of X-ray emitting gas in galaxy clusters, especially at large radii, can be used to place constraints on cluster gas physics, making it potential probes of the history of baryonic cooling in galaxy clusters.
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机译：最近的星团形成模拟表明，在星团形成过程中重子凝结到中心星系中，可以驱动星团中气体分布的形状显着变圆至其病毒半径。这些模拟通常预测星团病毒半径内的恒星分数比从观测结果推导出的恒星质量大约2-3倍。在本文中，我们将通过改变输入物理学（辐射冷却，恒星形成和超新星反馈）执行的模拟星团的椭圆率轮廓与从钱德拉和ROSAT观测得到的星团椭圆率轮廓进行比较，以限制冷却气体的比例并凝结成团内的中央星系。我们发现在0.04≤r / r 500≤1的径向范围内，局部松弛簇的平均椭圆度= = 0.18±0.05。在较大半径r> 0.1r 500时，观察到的椭圆度轮廓与非椭圆形的预测非常吻合。辐射模拟。相反，包括耗散气体物理学在内的模拟团簇的椭圆率轮廓与在所有半径处观察到的椭圆率轮廓有很大的偏差。耗散模拟高估（低估）星系团内部（外部）区域的椭圆率。通过比较有和没有耗散气体物理条件的模拟，我们表明气体冷却导致气体分布在中心区域更加扁平，但使外部气体分布更加球形。我们发现，后期气体冷却和恒星形成是造成团簇核中明显扁圆的气体分布的原因，但团簇核外的气体形状主要是由高红移（z≥2）处的重子耗散来设定的。我们的结果表明，星系团簇中发出X射线气体的形状，特别是在大半径处，可以用来限制团簇气体的物理性质，使其成为星系团中重子冷却历史的潜在探查。
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