The ALMA-QUARKS Survey: Fibers’ role in star formation unveiled in an intermediate-mass protocluster region of the Vela D cloud

In this paper, we present a detailed analysis of the IRS 17 filament within the intermediate-mass protocluster IRAS 08448-4343 (of ∼ 103 L⊙), using ALMA data from the ATOMS 3-mm and QUARKS 1.3-mm surveys. The IRS 17 filament, which spans ∼54000 au (0.26 pc) in length and ∼4000 au (0.02 pc) in width, exhibits a complex, multi-component velocity field, and harbours hierarchical substructures. These substructures include three bundles of seven velocity-coherent fibers, and 29 dense (n ∼ 108 cm−3) condensations. The fibers have a median length of ∼ 4500 au and a median width of ∼ 1400 au. Among these fibers, four are identified as “fertile”, each hosting at least three dense condensations, which are regarded as the “seeds” of star formation. While the detected cores are randomly spaced within the IRS 17 filament based on the 3-mm dust continuum image, periodic spacing (∼ 1600 au) of condensations is observed in the fertile fibers according to the 1.3-mm dust map, consistent with the predictions of linear isothermal cylinder fragmentation models. These findings underscore the crucial role of fibers in star formation and suggest a hierarchical fragmentation process that extends from the filament to the fibers, and ultimately, to the smallest-scale condensations.

本研究针对位于中等质量原星团IRAS 08448-4343（光度约10³倍太阳光度，L⊙）内部的IRS 17丝状体开展了详细分析，所用数据来自ATOMS 3毫米波段与QUARKS 1.3毫米波段的阿塔卡马大型毫米/亚毫米波阵列（ALMA）巡天项目。该IRS 17丝状体的长度约为54000天文单位（0.26秒差距），宽度约为4000天文单位（0.02秒差距），呈现出复杂的多分量速度场，并蕴含层级化子结构。这些子结构包含3组共7条速度相干纤维状结构，以及29个密度约为10⁸ cm⁻³的致密凝块。这些纤维状结构的中位长度约为4500天文单位，中位宽度约为1400天文单位。其中4条纤维状结构被判定为“富产型”，每条至少包含3个致密凝块——这些凝块被视作恒星形成的“种子”。基于3毫米波段尘埃连续谱图像，所探测到的恒星形成核在IRS 17丝状体内部呈随机分布；但在1.3毫米波段尘埃分布图中，富产型纤维状结构内的致密凝块呈现出约1600天文单位的周期性间距，这与线性等温圆柱碎裂模型的理论预言相符。上述研究结果凸显了纤维状结构在恒星形成过程中的关键作用，并揭示了一套层级化碎裂过程：该过程从丝状体延伸至纤维状结构，最终细化至最小尺度的致密凝块。