arXiv 1709.007092017-09-03astro-ph.GAastro-ph.CO

星系际介质的引力坍缩预热和紫外背景

Pre-heating of the intergalactic medium by gravitational collapse and ultraviolet background

Weishan Zhu, Long-Long Feng

备注：: 18 pages, 11 figures, To appear in ApJ
DOI：: 10.3847/1538-4357/aa88d2

摘要：

在宇宙流体动力学模拟中，研究了星系际介质结构坍缩和紫外背景辐射对星系际介质的预热作用。当引力坍缩是唯一的加热机制时，我们发现：（1）在$z=0$，IGM的$60\%, 45\%$分别被加热到$S>8, 17$ kev cm $^2$，但在$z=2$，$60\%, 45\%$的分数迅速下降到几个单位;（2）从$z=2$开始，环晕气体$S_{\rm{cir}}$的熵大于质量为$M<10^{11.5}$ $M_{\odot}$的晕的维里熵，但在星系形成的预防模型中，当$M<10^{10.5} M_{\odot}$处于$z=0$时，所需的高于熵的部分$S_{\rm{pr}}$仅为$15-20 \%$，且随红移的增加而减小;（3）假设金属丰度为$Z \leq 0.03 Z_{\odot}$，则环晕气体冷却时间长于哈勃时间的部分$t_{cool,cir}>t_{\rm{H}}$仅为$5-10 \%$ at $z \lesssim 0.5$，而在$z \geq 1$使用$M<10^{10.5} M_{\odot}$进行晕圈测试的情况更少。(4)灯丝中的气体经历最强的预热。此外，我们还发现，UVB并不能增加IGM与$S>17$ kev cm $^2$的比例，但可以增加低质量晕（$<10^{10.5} M_{\odot}$）的比例，即在$z=0$处由$S_{\rm{cir}}>S_{\rm{pr}}$变为$\sim 70 \%$，以及在$z \lesssim 0.5$处由$t_{\rm{cool, cir}}>t_{\rm{H}}$变为$15-30 \%$。我们的研究结果表明，由于重力坍缩和UVB预热是不足以满足预防模型的需要，特别是与$10^{10.5}<M<10^{11.5} M_{\odot}$晕。然而，这两种机制可能会导致大规模的星系整合。

英文摘要：

The preheating of intergalactic medium(IGM) by structure collapsing and ultraviolet background(UVB) are investigated in cosmological hydrodynamical simulations. When gravitational collapsing is the sole heating mechanism, we find that (1) $60\%, 45\%$ of the IGM are heated up to $S>8, 17$ kev cm$^2$ respectively at $z=0$, but the fractions drop rapidly to a few percents at $z=2$, (2) the entropy of the circum-halo gas $S_{\rm{cir}}$ is higher than the virial entropy for more than $75 \%$ of the halos with masses $M<10^{11.5}$ $M_{\odot}$ since $z=2$, but the fraction higher than the entropy, $S_{\rm{pr}}$, required in preventive model of galaxies formation is only $15-20 \%$ for halos with $M<10^{10.5} M_{\odot}$ at $z=0$, and decreases as redshift increases, (3)assuming a metallicity of $Z \leq 0.03 Z_{\odot}$, the fraction of halos whose circum-halo gas having a cooling time longer than the Hubble time $t_{cool,cir}>t_{\rm{H}}$ is merely $5-10 \%$ at $z \lesssim 0.5$, and even less at $z \geq 1$ for halos with $M<10^{10.5} M_{\odot}$. (4) gas in the filaments undergoes the strongest preheating. Furthermore, we show that the UVB can not enhance the fraction of IGM with $S>17$ kev cm$^2$, but can increase the fraction of low mass halos($<10^{10.5} M_{\odot}$) that having $S_{\rm{cir}}>S_{\rm{pr}}$ to $\sim 70 \%$ at $z=0$, and that having $t_{\rm{cool, cir}}>t_{\rm{H}}$ to $15-30 \%$ at $z \lesssim 0.5$. Our results indicate that preheating due to gravitational collapsing and UVB are inadequate to fulfil the needs of preventative model, especially for halos with $10^{10.5}<M<10^{11.5} M_{\odot}$. Nevertheless, these two mechanisms might cause large scale galactic conformity.

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