局部环境与全局环境：星系团周边恒星形成的抑制
Local versus global environment: the suppression of star formation in the vicinity of galaxy clusters
AI总结：
本研究利用射电巡天数据探究星系团周边恒星形成熄灭机制，发现SFG比例在远至 $10R_{500}$ 处即下降，且受星系质量、局部与全局环境复杂相互作用的共同影响。
摘要：
为了探究星系团外围恒星形成熄灭的起始位置、方式及原因，我们研究了一大批熄灭星系和恒星形成星系（SFGs）在星系团周围直至 $30R_{500}$ 范围内的去投影径向分布。我们利用低频阵列两米巡天的射电连续辐射来证认SFG样本。我们发现，SFG比例在远至 $10R_{500}$ 处就开始偏离场星系比例下降，这远在星系团的位力半径之外。我们研究了SFG比例如何依赖于大尺度和局部环境，使用距离星系团的径向距离表征大尺度环境，使用距离第五近邻星系的距离表征局部环境。高密度局部环境中的SFG比例始终低于低密度局部环境，表明星系紧邻的周围环境对恒星形成有显著影响。然而，对于高质量星系（以及较低程度上的低质量星系），高密度局部环境似乎充当了那些在预处理中幸存下来的SFG的保护屏障，使它们免受星系团外围外部熄灭机制的影响。对于不在密集局部环境中的星系，全局环境导致SFG比例向星系团中心下降，且该方式与星系质量无关。因此，SFG的比例取决于星系质量、局部环境及其更全局的以星系团为中心距离之间相当复杂的相互作用。
英文摘要：
In order to examine where, how and why the quenching of star formation begins in the outskirts of galaxy clusters, we investigate the de-projected radial distribution of a large sample of quenched and star-forming galaxies (SFGs) out to $30R_{500}$ around clusters. We identify the SFG sample using radio continuum emission from the Low-Frequency Array Two-metre Sky Survey. We find that the SFG fraction starts to decrease from the field fraction as far out as $10R_{500}$, well outside the virial radius of the clusters. We investigate how the SFG fraction depends on both large-scale and local environments, using radial distance from a cluster to characterise the former, and distance from 5th nearest neighbour for the latter. The fraction of SFGs in high-density local environments is consistently lower than that found in low-density local environments, indicating that galaxies' immediate surroundings have a significant impact on star formation. However, for high-mass galaxies -- and low mass galaxies to a lesser extent -- high-density local environments appear to act as a protective barrier for those SFGs that survived this pre-processing, shielding them from the external quenching mechanisms of the cluster outskirts. For those galaxies that are not in a dense local environment, the global environment causes the fraction of SFGs to decrease toward the cluster centre in a manner that is independent of galaxy mass. Thus, the fraction of SFGs depends on quite a complex interplay between the galaxies' mass, their local environment, and their more global cluster-centric distance.
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