New Insights into Lyman Limit Systems in Galaxy Environments

Recent research has focused on a multiphase Lyman limit system (LLS) identified at redshift $z=0.39047$ towards the quasar FBQS J0209-0438. The study, titled "Lyman Limit System with O VI in the Circumgalactic Environment of a Pair of Galaxies," reveals that the O VI doublet lines associated with this absorber exhibit a distinct profile compared to low ionization metals and hydrogen (H I). Notably, the Lyα line shows a broad H I component with a Doppler parameter of approximately 150 km/s, which is well-aligned with one of the O VI components.

The analysis indicates that the gas temperature ranges between $(0.8-2.0) \times 10^6$ K, with a total hydrogen column density significantly larger than that of the cooler gas phase responsible for the LLS. Observations conducted using the VLT/MUSE instrument identified two moderately star-forming galaxies located within 105 kpc and with a velocity difference of less than 130 km/s from the absorber. One of these is a dwarf galaxy with a stellar mass of about $10^6$ M$\odot$, while the other is a larger galaxy with a stellar mass of approximately $3 \times 10^{10}$ M$\odot$.

The findings suggest that the absorption is aligned with the extended major axis of the larger galaxy, although the velocity of the absorbing gas does not support the idea of corotating accretion. Furthermore, the metallicity of the LLS is found to be lower than that of the gas phase in both galaxies. This mixture of cool and warm/hot gas phases, along with the proximity and orientation to the galaxy pair, indicates that the LLS is likely high-velocity gas within the combined halo environment of both galaxies. The implications of this research contribute to the understanding of galaxy formation and the dynamics of circumgalactic environments.