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arXiv 0901.1317astro-ph.CO
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解析星系形成:I.纯暗物质与重子模型的比较

Dissecting Galaxy Formation: I. Comparison Between Pure Dark Matter and Baryonic Models

Emilio Romano-Diaz, Isaac Shlosman, Clayton Heller, Yehuda Hoffman

摘要:

我们比较组装的DM晕和没有重子,在宇宙演化的背景下,在LCDM WMAP 3宇宙(重子+DM,BDM模型,和纯DM,PDM模型)。在有代表性的PDM和BDM模型中,我们发现重子对中心区域的演化有决定性的贡献,导致等温DM尖点,以及平坦的DM密度核心--在静止演化时期由子结构的动态摩擦加热的结果。这一过程从一个嵌入的盘中烧蚀冷气体,使恒星形成率降低约10,并加热球状气体和恒星成分,引发它们的膨胀。在重子的存在下,子结构更有弹性。根据气体含量和球盘恒星质量比,由内向外形成的气体盘在z ~ 2时转变为哈勃中期型,z ~ 0.5时转变为早期型。在PDM和BDM模型中,只有相对较小的~20%的DM粒子被束缚在晕中的最大圆速度半径内-大多数DM粒子执行较大的径向偏移。我们还发现,在晕维里半径的重子的分数有所增加,在主要合并和减少,在次要合并。净效应似乎可以忽略不计。当子结构被潮汐破坏时,其碎片在晕中的混合效率不高,并且随着z的增加而变得更低。在z ~ 1之后形成的流光大部分保留到了现在--这是嵌入盘演化的一个重要暗示。

英文摘要:

We compare assembly of DM halos with and without baryons, within the context of cosmological evolution in the LCDM WMAP3 Universe (baryons+DM, BDM model, and pure DM, PDM model). In representative PDM and BDM models we find that baryons contribute decisively to the evolution of the central region, leading to an isothermal DM cusp, and to a flat DM density core -- the result of heating by dynamical friction of the substructure during a quiescent evolution epoch. This process ablates the cold gas from an embedded disk, cutting the star formation rate by ~10, and heats up the spheroidal gas and stellar components, triggering their expansion. The substructure is more resilient in the presence of baryons. The disk which formed from inside-out as gas dominated, is transformed into an intermediate Hubble type by z ~ 2 and to an early type by z ~ 0.5, based on its gas contents and spheroidal-to-disk stellar mass ratio. Only a relatively small ~20% fraction of DM particles in PDM and BDM models are bound within the radius of maximal circular velocity in the halo -- most of the DM particles perform larger radial excursions. We also find that the fraction of baryons within the halo virial radius somewhat increases during the major mergers and decreases during the minor mergers. The net effect appears to be negligible. While the substructure is being tidally-disrupted, mixing of its debris in the halo is not efficient and becomes even less so with z. The streamers formed after z ~ 1 survive largely to the present time -- an important implication for embedded disk evolution.

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