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arXiv 0908.1309astro-ph.GA
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星团内介质的金属富集:SN驱动的星系风

Metal enrichment of the intracluster medium: SN-driven galactic winds

Verena Baumgartner, Dieter Breitschwerdt

摘要:

我们研究了超新星驱动的星系风在团内介质化学富集中的作用。星系尺度上的这种外流起源于巨大的恒星形成区,并将富含金属的物质从星系中驱逐到周围,例如在附近的星暴星系NGC 253中观察到的。当OB-associations中的大质量恒星相继爆炸时,冲击波被驱动到星系的星际介质中并合并,形成超级气泡(SB)。这些SB沿着ISM的密度梯度在垂直于盘平面的方向上扩展。我们使用Kompaneets(1960)的二维解析近似来模拟指数分层ISM中SB的扩展。这是修改,以描述SN爆炸的序列作为一个时间依赖的过程,考虑到SN-祖先的主序星的寿命,并使用初始质量函数,以获得每个质量间隔的大质量恒星的数量。解析计算了气泡在空间和时间上的演化,由此可以确定壳体中瑞利-泰勒不稳定性的发生。在其进一步的演化过程中,壳层将破裂,高金属含量的气体将被喷射到星系的晕中,甚至进入ICM。我们推导出的恒星数量需要井喷取决于规模的高度和密度的环境介质,以及分数的α和铁峰元素包含在热气体。最后,银河系型星系注入ICM的金属量的计算证实了这一富集过程的重要性。

英文摘要:

We investigate the role of supernova (SN)-driven galactic winds in the chemical enrichment of the intracluster medium (ICM). Such outflows on galactic scales have their origin in huge star forming regions and expel metal enriched material out of the galaxies into their surroundings as observed, for example, in the nearby starburst galaxy NGC 253. As massive stars in OB-associations explode sequentially, shock waves are driven into the interstellar medium (ISM) of a galaxy and merge, forming a superbubble (SB). These SBs expand in a direction perpendicular to the disk plane following the density gradient of the ISM. We use the 2D analytical approximation by Kompaneets (1960) to model the expansion of SBs in an exponentially stratified ISM. This is modified in order to describe the sequence of SN-explosions as a time-dependent process taking into account the main-sequence life-time of the SN-progenitors and using an initial mass function to get the number of massive stars per mass interval. The evolution of the bubble in space and time is calculated analytically, from which the onset of Rayleigh-Taylor instabilities in the shell can be determined. In its further evolution, the shell will break up and high-metallicity gas will be ejected into the halo of the galaxy and even into the ICM. We derive the number of stars needed for blow-out depending on the scale height and density of the ambient medium, as well as the fraction of alpha- and iron peak elements contained in the hot gas. Finally, the amount of metals injected by Milky Way-type galaxies to the ICM is calculated confirming the importance of this enrichment process.

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