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arXiv 1407.7129astro-ph.GAastro-ph.CO
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高z星系中angular-momentum形成的四个阶段:从宇宙网流通过扩展环到盘和隆起

Four phases of angular-momentum buildup in high-z galaxies: from cosmic-web streams through an extended ring to disc and bulge

Mark Danovich, Avishai Dekel, Oliver Hahn, Daniel Ceverino, Joel Primack

摘要:

利用高分辨率宇宙学模拟研究了高$z$质量星系的角动量(AM)积累。AM起源于冷气体的共面流和追踪宇宙网细丝的合并星系,它经历了四个演化阶段。(I)在晕维里半径($R_{\rm v}\!\sim\!100\,{\rm kpc}$)之外,由于气体的四极矩更高,伸长的流通过潮汐力矩获得AM,具有特定的AM(sAM)$\sim\!1.7$乘以暗物质(DM)自旋。该AM表示为从$\sim\!0.3R_{\rm v}$到反向旋转的流碰撞参量。(II)在外晕中,当进入的DM与较低sAM的现有晕混合成自旋$λ_{\rm dm}\!\sim\!0.04$时,冷流将AM输送到内晕,使得它们在晕中的自旋为$\sim\!3λ_{\rm dm}$。(III)在近中心附近,气流消散成不规则的旋转环,延伸至$\sim\!0.3R_{\rm v}$,并相对于内盘倾斜。部分由圆盘施加的扭矩使环气体失去AM,螺旋进入,并在一个轨道内进入圆盘。该环作为阻尼Lyman- $α$吸收体可以30%的概率观测到。(IV)在圆盘$<\!0.1R_{\rm v}$中,与剧烈的圆盘不稳定性相关的扭矩将AM和重子驱动到中央隆起中,而外流则带走了低自旋气体,从而对反馈强度产生了一定的敏感性。尽管气体和DM的AM历史不同,但盘的自旋与DM-晕的自旋相当。逆旋转可以强烈地影响盘的演化。

英文摘要:

We study the angular-momentum (AM) buildup in high-$z$ massive galaxies using high-resolution cosmological simulations. The AM originates in co-planar streams of cold gas and merging galaxies tracing cosmic-web filaments, and it undergoes four phases of evolution. (I) Outside the halo virial radius ($R_{\rm v}\!\sim\!100\,{\rm kpc}$), the elongated streams gain AM by tidal torques with a specific AM (sAM) $\sim\!1.7$ times the dark-matter (DM) spin due to the gas' higher quadrupole moment. This AM is expressed as stream impact parameters, from $\sim\!0.3R_{\rm v}$ to counter rotation. (II) In the outer halo, while the incoming DM mixes with the existing halo of lower sAM to a spin $λ_{\rm dm}\!\sim\!0.04$, the cold streams transport the AM to the inner halo such that their spin in the halo is $\sim\!3λ_{\rm dm}$. (III) Near pericenter, the streams dissipate into an irregular rotating ring extending to $\sim\!0.3R_{\rm v}$ and tilted relative to the inner disc. Torques exerted partly by the disc make the ring gas lose AM, spiral in, and settle into the disc within one orbit. The ring is observable with 30\% probability as a damped Lyman-$α$ absorber. (IV) Within the disc, $<\!0.1R_{\rm v}$, torques associated with violent disc instability drive AM out and baryons into a central bulge, while outflows remove low-spin gas, introducing certain sensitivity to feedback strength. Despite the different AM histories of gas and DM, the disc spin is comparable to the DM-halo spin. Counter rotation can strongly affect disc evolution.

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