Parkes observations for project P1219 semester 2025APRS_02

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中起着基础性作用。塞曼分裂为直接测量星际环境（从弥散星际介质（ISM）到致密核区）中的视向磁场强度提供了独特方法。对脉冲星方向的HI和OH吸收线观测，借助脉冲星小角径及不受仪器效应影响的可靠斯托克斯V（Stokes V）光谱，为高精度测量磁场提供了前所未有的机遇。我们近期利用Parkes望远镜对PSR J1644-4559方向OH吸收线进行的初步塞曼分裂探测，揭示的磁场强度表明其处于磁亚临界状态——即磁压足以抵消引力。这对亚临界冷中性介质（CNM）向超临界恒星形成分子云转变的传统理论提出了挑战，凸显了深入研究的必要性。我们提议利用Parkes望远镜对脉冲星PSR J1644-4559、J1721-3532及J1852+0031开展高灵敏度OH和HI吸收线观测，以延续塞曼分裂研究。通过采用创新的相位分辨光谱技术并延长积分时间，我们旨在提升塞曼探测灵敏度，研究CNM与宁静分子云中的磁场转变。此项工作将深化我们对恒星形成中亚临界向超临界转变的理解，确立脉冲星吸收线作为星际磁场可靠探针的地位，并推动对恒星形成研究至关重要的观测技术发展。