2020ApJ...892...33R

We explore the possibility to systematically study the extended, hot gaseous halos of low-redshift galaxies with coronal broad Lyα absorbers (CBLAs). These are weak, thermally broadenend H I absorption lines arising from the tiny fraction of neutral hydrogen that resides in the collisionally ionized, million-degree halo gas in these galaxies. Using a semi-analytic approach, we model the spatial density and temperature distribution of hot coronal gas to predict strength, spectral shape, and cross section of CBLAs as a function of galaxy-halo mass and line-of-sight impact parameter. For virial halo masses in the range log (M/M_☉)=10.6–12.6, the characteristic logarithmic CBLA H I column densities and Doppler parameters are log N(H I) = 12.4-13.4 and b(H I) = 70-200 km s^–1, indicating that CBLAs represent weak, shallow spectral features that are difficult to detect. Yet, the expected number density of CBLAs per unit redshift in the above given mass range is d N/dz(CBLA) ≃ 3, implying that CBLAs have a substantial absorption cross section. We compare the model predictions with a combined set of UV absorption-line spectra from the Hubble Space Telescope (HST)/Cosmic Origins Spectrograph and HST/Space Telescope Imaging Spectrograph that trace the halos of four low-redshift galaxies. We demonstrate that CBLAs might already have been detected in these spectra, but the complex multi-component structure and the limited signal-to-noise ratio complicate the interpretation of these CBLA candidate systems. Our study suggests that CBLAs represent a very interesting absorber class that potentially will allow us to further explore the hot coronae of galaxies with UV spectral data.