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

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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.