Parkes observations for project P1219 semester 2025APRS_03

Magnetic fields are fundamental in regulating star formation and the evolution of molecular clouds. Zeeman splitting offers a unique method to directly measure line-of-sight magnetic field strengths in interstellar environments, from the diffuse ISM to dense cores. Observations of HI and OH absorption toward pulsars provide an unprecedented opportunity to measure magnetic fields with high precision, benefiting from pulsars' small angular sizes and reliable Stokes V spectra unaffected by instrumental effects. Our recent tentative Zeeman splitting detections in OH absorption toward PSR J1644-4559 with Parkes reveal magnetic field strengths that suggest magnetically subcritical states, where magnetic pressure counteracts gravity. This challenges conventional theories of subcritical cold neutral medium (CNM) transitioning to supercritical star-forming molecular clouds, emphasizing the need for detailed investigation. We propose a continuation of Zeeman splitting studies through high-sensitivity OH and HI absorption observations of pulsars PSR J1644-4559, J1721-3532, and J1852+0031 using Parkes. By employing an innovative phase-resolved spectral technique and extending integration times, we aim to enhance Zeeman detection sensitivity and study magnetic field transitions in the CNM and quiescent molecular clouds. This work will refine our understanding of subcritical-to-supercritical transitions in star formation, establish pulsar absorption as a robust probe of interstellar magnetic fields, and advance observational techniques critical to star formation studies.

磁场在调控恒星形成与分子云演化进程中发挥着基础性作用。塞曼分裂（Zeeman splitting）是一种独特的直接测量方法，可用于获取星际环境中从弥散星际介质（diffuse ISM）到致密核的视向磁场强度。针对脉冲星（pulsar）的中性氢（HI）与羟基（OH）吸收观测，得益于脉冲星极小的角尺度以及不受仪器效应干扰的可靠斯托克斯V谱（Stokes V），为高精度测量星际磁场提供了前所未有的契机。我们近期利用帕克斯望远镜（Parkes）对脉冲星PSR J1644-4559方向的OH吸收谱开展的初步塞曼分裂探测结果显示，该区域磁场处于磁亚临界态——此时磁压可与引力形成抗衡。这一发现对“冷中性介质（cold neutral medium, CNM）从亚临界态向恒星形成型超临界分子云过渡”的传统理论提出了挑战，凸显了开展系统性深入研究的必要性。我们提议延续塞曼分裂相关研究，利用帕克斯望远镜对脉冲星PSR J1644-4559、PSR J1721-3532及PSR J1852+0031开展高灵敏度的OH与HI吸收观测。通过采用创新性的相位分辨光谱技术并延长积分时长，我们旨在提升塞曼分裂的探测灵敏度，进而研究冷中性介质与宁静分子云中的磁场过渡机制。本研究将完善我们对恒星形成过程中亚临界态向超临界态过渡的认知，确立脉冲星吸收作为星际磁场可靠探针的地位，并推动恒星形成研究所需的关键观测技术的发展。