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

星系被大量弥漫的气体包围着，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）在星系演化中起着重要作用。冲击加热的热CGM相（“电晕”）包含CGM的主要质量分数，但由于非常低的气体密度和非常高的电离度，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，通过所谓的日冕宽莱曼阿尔法吸收器（CBLA）来研究本地宇宙中星系周围的热日冕气体。这些是在背景点源的紫外（UV）光谱中看到的宽而浅的HI吸收特征。CBLA产生于前景星系热气晕中微小的中性气体部分。我们将利用HST/COS光谱仪的紫外光谱数据，系统地研究红移z<0.5的约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。观测方法将得到补充的系统研究CBLA在合成光谱产生的数值磁流体动力学模拟的CGM。从HST/COS光谱数据和模拟的大CBLA样本的组合将使我们能够更好地了解广泛的莱曼阿尔法功能，从星系的热气晕产生的性质，并探索其重要性，观测约束星系演化模型。

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.