Title: Evidence for a gas-rich major merger in a proto-cluster at z=2.5 Show Chinese title

Title: z=2.5 原星团中富含气体的主要合并的证据

Abstract: Gas-rich major mergers in high-redshift proto-clusters are important events, perhaps leading to the creation of the slowly rotating remnants seen in the cores of clusters in the present day. Here, we present a deep Jansky Very Large Array observation of CO J = 1-0 emission line in a proto-cluster at z = 2.5, USS1558-003. The target field is an extremely dense region, where 20 H-alpha emitters (HAEs) are clustering. We have successfully detected the CO emission line from three HAEs and discovered a close pair of red and blue CO-emitting HAEs. Given their close proximity (~30 kpc), small velocity offset (~300 km/s), and similar stellar masses, they could be in the early phase of a gas-rich major merger. For the red HAE, we derive a total infrared luminosity of L(IR)=5.1e12 Lsun using MIPS 24 um and radio continuum images. The L(IR)/L'(CO) ratio is significantly enhanced compared to local spirals and high-redshift disks with a similar CO luminosity, which is indicative of a starburst mode. We find the gas depletion timescale is shorter than that of normal star-forming galaxies regardless of adopted CO-H2 conversion factors. The identification of such a rare event suggests that gas-rich major mergers frequently take place in proto-clusters at z > 2 and may involve the formation processes of slow rotators seen in local massive clusters. Show Chinese abstract

Abstract: 高红移原星团中的富含气体的主要并合事件是重要的事件，或许导致了如今在星团核心处观察到的缓慢旋转遗迹的形成。 在这里，我们展示了针对红移 z = 2.5 的原星团 USS1558-003 中 CO J = 1-0 发射线的深度 Jansky 非常大阵列观测结果。 目标区域是一个极其密集的区域，在其中聚集了 20 个氢α发射线星（HAEs）。 我们成功地从三个 HAEs 检测到了 CO 发射线，并发现了一对红色和蓝色 CO 发射线 HAEs 的近距离配对。 鉴于它们之间的近距离（~30 千秒差距）、小的速度偏移（~300 公里/秒）以及相似的恒星质量，它们可能处于富含气体的主要并合事件的早期阶段。 对于红色 HAE，我们使用 MIPS 24 微米和射电连续谱图像推导出总红外亮度为 L(IR)=5.1e12 Lsun。 与具有相似 CO 辐射亮度的本地螺旋星系和高红移盘状星系相比，L(IR)/L'(CO) 比值显著增强，这表明了爆发性星系形成的模式。 我们发现，无论采用何种 CO-H2 转换因子，气体耗尽的时间尺度都比正常恒星形成星系的短。 这种罕见事件的识别表明，在 z > 2 的原星团中频繁发生富含气体的主要并合事件，并且可能涉及在本地大质量星团中所见的慢速旋转星系的形成过程。