半解析模型和SPH模拟中的气体冷却：结果一致吗？
Gas cooling in semi-analytic models and SPH simulations: are results consistent?
摘要：
我们提出了一个详细的比较大规模集群内的星系人口，流体动力学SPH模拟和半解析模型（SAM）的星系形成预测。这两个模型都包括气体冷却和恒星形成的简单处方，即将任何冷气体瞬间转化为恒星，同时忽略任何能量反馈源。我们发现，在一般情况下，星系人口从自组装和SPH有类似的统计特性，与以前的研究。然而，当我们逐个比较星系时，我们发现了一些有趣的差异：a）SAM和SPH模型计算的最亮星系团（BCGs）的恒星形成历史有很大的不同，SPH BCGs在低红移时表现出较低的恒星形成活动水平，并且相对于SAM对应物，其恒星形成的初始爆发更强烈和更短; b）虽然在这里使用的半解析模型中，所有与BCG相关的恒星都是在其祖先中形成的，但在SPH模拟中，这只适用于最终BCG恒星质量的一半，剩下的一半是由恒星从与星系团晕上吸积的星系相关的弥漫恒星成分中潮汐剥离所贡献的;（c）SPH卫星在吸积时可由于潮汐剥离而失去高达90%的恒星质量，这一过程未包括在本研究所用的半分析模型中;（d）在SPH模拟中，大部分质量卫星星系都发生了显著的冷却，吸积后这种冷却可持续1 Gyr。这个物理过程不包括在我们的研究中使用的半解析模型，以及在最近的文献中讨论的大多数模型。
英文摘要：
We present a detailed comparison between the galaxy populations within a massive cluster, as predicted by hydrodynamical SPH simulations and by a semi-analytic model (SAM) of galaxy formation. Both models include gas cooling and a simple prescription of star formation, which consists in transforming instantaneously any cold gas available into stars, while neglecting any source of energy feedback. We find that, in general, galaxy populations from SAMs and SPH have similar statistical properties, in agreement with previous studies. However, when comparing galaxies on an object-by-object basis, we find a number of interesting differences: a) the star formation histories of the brightest cluster galaxies (BCGs) from SAM and SPH models differ significantly, with the SPH BCG exhibiting a lower level of star formation activity at low redshift, and a more intense and shorter initial burst of star formation with respect to its SAM counterpart; b) while all stars associated with the BCG were formed in its progenitors in the semi-analytic model used here, this holds true only for half of the final BCG stellar mass in the SPH simulation, the remaining half being contributed by tidal stripping of stars from the diffuse stellar component associated with galaxies accreted on the cluster halo; c) SPH satellites can loose up to 90 per cent of their stellar mass at the time of accretion, due to tidal stripping, a process not included in the semi-analytic model used in this study; d) in the SPH simulation, significant cooling occurs on the most massive satellite galaxies and this lasts for up to 1 Gyr after accretion. This physical process is not included in the semi-analytic model used in our study, as well as in most of the models discussed in the recent literature.
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