A UV survey of hot, coronal gas in the halos of low-redshift galaxies

星系被大量弥散的气体包围，这些气体存在于它们延伸的暗物质晕中。这种所谓的环星系介质(CGM)在星系演化中扮演着重要的角色。激波加热的CGM相(“日冕”)包含CGM的主要质量分数，但由于气体密度很低和电离度很高，很难直接观察到。在这个博士项目中，我们将使用一种新的方法来研究局部宇宙中星系周围的高温日冕气体，即所谓的日冕广域莱曼阿尔法吸收体(CBLA)。这些都是在背景点源的紫外线(UV)光谱中看到的宽而浅的HI吸收特征。CBLA是由前景星系的热气晕中的微小中性气体组成的。我们将利用HST/COS光谱仪的记录紫外光谱数据，系统地研究红移z&lt；0.5处的~50个CBLA的性质，并限制相关前景星系中日冕气体的范围和物理性质。对观测方法的补充将是对CGM的数值磁流体力学模拟所产生的合成光谱中的CBLA进行系统研究。来自HST/COS光谱数据的大CBLA样本与模拟相结合，将使我们能够更好地理解星系热气晕产生的广泛Lyman Alpha特征的性质，并探索它们对观测约束星系演化模型的重要性。

Galaxies are surrounded by huge amounts of diffuse gas that resides in their extended dark-matter halos. This so-called circumgalactic medium (CGM) plays an important role for galaxy evolution. The shock-heated, hot CGM phase (the “Corona”) contains the dominant mass fraction of the CGM, but is very difficult to be observed directly because of the very low gas densities and a very high degree of ionization. In this PhD project, we will use a new method to study the hot coronal gas around galaxies in the local Universe by way of so-called Coronal Broad Lyman Alpha Absorbers (CBLAs). These are broad and shallow HI absorption features seen in the ultraviolet (UV) spectra of background point sources. CBLAs arise from the tiny neutral gas fraction in the hot gas halos of foreground galaxies. We will use archival ultraviolet spectral data from the HST/COS spectrograph to systematically study the properties of ~50 CBLAs at redshifts z<0.5 and constrain the extent and physical properties of the coronal gas in the associated foreground galaxies. The observational approach will be supplemented with the systematic study of CBLAs in synthetic spectra generated from numerical magneto-hydrodynamic simulations of the CGM. The combination of a large CBLA sample from HST/COS spectral data and simulations will enable us to better understand the nature of the broad Lyman Alpha features that arise from the hot gas halos of galaxies and explore their importance for observationally constraining galaxy-evolution models.