Origins, distribution and kinematics of circumgalactic O VI around star forming L* galaxies

Abstract

Analysing the state of the art, zoom-in simulation "Eris", we study the distribution, origins and kinematics of O~VI gas around star forming L* galaxies. A detailed comparison to observations from the COS-halo survey is made, by generating sightlines through the simulated halo and examining the properties of the gas along them. At $z \sim$ 0, the O~VI column density is between $10^{14}$ and $10^{15}$ cm$^{-2}$ up to 300 kpc, consistent with the COS-halo data. This column density appears to remain unchanged from $z=3$ to $z=0$ in the range of 10-100 kpc, which is at least partially explained by an expanding O~VI bubble. O~VI rich gas particles in Eris are tracked from $z=0$ to $z=3$, with the aim of finding the origin of the circumgalactic O~VI gas. The result demonstrates that most of the O~VI rich corona gas in Eris is be enriched and heated by supernova feedback at early times, in contrast with the classical interpretation of hot mode shock accretion. The majority of the O~VI bearing gas is outflowing at all times, but the inflowing component increases with time. The mass distribution of the circumgalactic O~VI peaks at the virial radii for all redshifts. The majority of the gas traced by O~VI is warm-hot corona gas with temperature $10^5$ K $<$ T $<10^6$ K, and the density of the O~VI gas is around $10^{-5}-10^{-4}$ cm$^{-3}$. The gas is mainly collisionally ionised, but photoionisation also has a non-negligible impact on O~VI abundance beyond 100 kpc. Synthetic O~VI spectra for the Eris simulation are generated in post-processing, and are fitted to find broadening parameters. With this we recreate the column density relation to broadening parameter seen in the COS-halo survey and other observations. Although the simulation successfully reproduces the observed column density distribution of O~VI and H~I, it underpredicts the column densities of low metallic ions, indicating the need of alternative non-thermal feedback, or a better resolution of the CGM in cosmological simulations.