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arXiv 0809.1430astro-ph
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模拟$Λ$ CDM宇宙I中的Galerkin:冷模和热核

Galaxies in a simulated $Λ$CDM Universe I: cold mode and hot cores

Dušan Kereš, Neal Katz, Mark Fardal, Romeel Dave, David H. Weinberg

摘要:

我们在一个(50 Mpc/h)^3的宇宙学模拟(2 × 288^3个粒子)中研究星系的形成,这个模拟是用熵守恒的SPH程序Gadget-2演化的。在所有质量的星系中,大多数重子质量最初是通过气体的间接“冷模”吸积获得的,这些气体从未被冲击加热到其晕维里温度,这证实了我们早期用不同的SPH代码获得的结果的关键特征(Keres et al. 2005)。在~2.5e11 Msun以上的晕中,热的维里化气体的大气层发展,过渡质量从z=3到z=0几乎是恒定的。冷吸积在过渡质量以上的晕中持续存在,特别是在z>=2时。它在任何时候都控制着低质量晕中星系的生长,是宇宙恒星形成历史的主要驱动力。卫星星系在高红移时的吸积率与相同重子质量的中心星系相似,但在低红移时,它们的吸积率比类似的中心星系要少。相对于我们早期的结果,Gadget-2模拟预测从大质量晕的维里化气体成分中的“热模式”吸积速率要低得多。在z<=1时,即使我们的模拟不包括活动星系核加热或其他形式的“预防性”反馈,在5e 12 Msun以上的晕中,典型的热吸积速率也低于1 Msun/年。在这些晕中的热气体的内部密度分布是浅的,与长的相关冷却时间。半解析模型中通常使用的冷却方法可能会高估这些晕中的吸积率,因此这些模型可能会过分强调预防性反馈在产生观测到的星系质量和颜色方面的作用。一小部分的大规模晕发展尖形轮廓和显着的冷却速率之间的z=1和z=0,红移趋势类似于观察到的趋势的频率冷却流团。

英文摘要:

We study the formation of galaxies in a (50 Mpc/h)^3 cosmological simulation (2x288^3 particles), evolved using the entropy conserving SPH code Gadget-2. Most of the baryonic mass in galaxies of all masses is originally acquired through filamentary "cold mode" accretion of gas that was never shock heated to its halo virial temperature, confirming the key feature of our earlier results obtained with a different SPH code (Keres et al. 2005). Atmospheres of hot, virialized gas develop in halos above ~2.5e11 Msun, a transition mass that is nearly constant from z=3 to z=0. Cold accretion persists in halos above the transition mass, especially at z>=2. It dominates the growth of galaxies in low mass halos at all times, and it is the main driver of the cosmic star formation history. Satellite galaxies have accretion rates similar to central galaxies of the same baryonic mass at high redshifts, but they have less accretion than comparable central galaxies at low redshift. Relative to our earlier results, the Gadget-2 simulations predict much lower rates of "hot mode" accretion from the virialized gas component of massive halos. At z<=1, typical hot accretion rates in halos above 5e12 Msun are below 1 Msun/yr, even though our simulation does not include AGN heating or other forms of "preventive" feedback. The inner density profiles of hot gas in these halos are shallow, with long associated cooling times. The cooling recipes typically used in semi-analytic models can overestimate the accretion rates in these halos by orders of magnitude, so such models may overemphasize the role of preventive feedback in producing observed galaxy masses and colors. A fraction of the massive halos develop cuspy profiles and significant cooling rates between z=1 and z=0, a redshift trend similar to the observed trend in the frequency of cooling flow clusters.

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