明亮的[CII]158μm流带作为SPT2349−56在z=4.3处巨大星系形成的灯塔
Bright [CII]158$μ$m Streamers as a Beacon for Giant Galaxy Formation in SPT2349$-$56 at $z=4.3$
AI总结：
SPT2349−56在z=4.3处的[CII]流带揭示了潮汐抛射对巨大星系形成的关键作用
摘要：
极端恒星burst的观测，通常位于原星团的核心，挑战了经典的自下而上星系形成范式。在z=0处的巨大椭圆星系必须迅速组装，可能在几亿年内通过高红移下的极端增长阶段，以每秒数千个太阳质量的恒星形成率分布在同时进行的气体丰富的并合中。我们通过敏感的多周期ALMA尘埃连续和[CII]158μm线观测，提出了z=4.3原星团核心SPT2349−56的新观点。分布在60kpc范围内，一个高度结构化的气体储备，具有线光度L_[CII]=3.0±0.2×10^9 L_⊙和推断的冷气体质量M_gas=8.9±0.7×10^9 M_⊙，发现围绕中心大质量星系三元组。像“珠链”一样，新发现的[CII]流带分裂成几个相隔数kpc的湍流团块，这些团块的气体柱密度与本地宇宙螺旋星系臂的Σ_gas=20-60 M_⊙ pc^{-2}相似。对于尘埃温度为30K，从被驱逐的团块中发射的[CII]辐射携带了约3%的远红外光度，转化为极低的质光比α_[CII]=2.95±0.3 M_⊙ L_⊙^{-1}，表明是受激的分子气体。在相空间中，大约一半的原星团核心中的星系占据与[CII]流带相同的caustic（r/r_vir×|Δv|/σ_vir≈0.1），表明通过潮汐抛射耗散角动量，同时最亮的星团星系（BCG）正在组装。我们的发现提供了新的证据，表明潮汐抛射[CII]明亮、受激材料的重要性，这些材料可能代表了z≥4时BCG与其热、金属富集大气共进化的关键阶段。
英文摘要：
Observations of extreme starbursts, often located in the cores of protoclusters, challenge the classical bottom-up galaxy formation paradigm. Giant elliptical galaxies at $z=0$ must have assembled rapidly, possibly within few 100 Myr through an extreme growth phase at high-redshift, characterized by elevated star-formation rates of several thousand solar masses per year distributed over concurrent, gas-rich mergers. We present a novel view of the $z=4.3$ protocluster core SPT2349$-$56 from sensitive multi-cycle ALMA dust continuum and [CII]158$μ$m line observations. Distributed across 60 kpc, a highly structured gas reservoir with a line luminosity of $L_\mathrm{[CII]}=3.0\pm0.2\times10^9$ $L_\odot$ and an inferred cold gas mass of $M_{gas}= 8.9\pm0.7\times10^{9}$ $M_\odot$ is found surrounding the central massive galaxy triplet. Like ``beads on a string'', the newly-discovered [CII] streamers fragment into a few kpc-spaced and turbulent clumps that have a similar column density as local Universe spiral galaxy arms at $Σ_{gas}=20$--$60$ $M_\odot$ pc$^{-2}$. For a dust temperature of 30 K, the [CII] emission from the ejected clumps carry $\gtrsim$3% of the FIR luminosity, translating into an exceptionally low mass-to-light ratio of $α_\mathrm{[CII]}=2.95\pm0.3$ $M_\odot$ $L_\odot^{-1}$, indicative of shock-heated molecular gas. In phase space, about half of the galaxies in the protocluster core populate the same caustic as the [CII] streamers ($r/r_{vir}\times|Δv|/σ_{vir}\approx0.1$), suggesting angular momentum dissipation via tidal ejection while the brightest cluster galaxy (BCG) is assembling. Our findings provide new evidence for the importance of tidal ejections of [CII]-bright, shocked material following multiple major mergers that might represent a landmark phase in the $z\gtrsim4$ co-evolution of BCGs with their hot, metal enriched atmospheres.
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