张华年，2011年获得山东大学物理学士，2016年毕业于亚利桑那大学物理，同年博士后入职亚利桑那大学Steward Observatory。张博士的主要研究领域在于用全新的方法研究星系外围的稀疏气体介质，取得了丰硕的成果。张博士的研究还包括用机器学习的方法寻找高红移 Quasar，以及通过理论和数值模拟来研究高红移星系和quasar的相关性。Galaxies are surrounded by extended and diffuse gas, referred to as the circumgalactic medium (CGM), which is a critical but incompletely understood part of galactic ecosystems. The CGM provides fuel for subsequent star formation activities and serves as the dumping ground for galactic recycling and feedback. The exceedingly low column density of gas in the CGM creates a significant observational challenge. The large spectroscopy survey like SDSS or DESI provides a statistical approach to study the CGM in detail. In this talk, I will introduce the method of the spectral absorption features and the emission lines to study the CGM, and how the CGM depends on the galaxy's various properties.