| Modern absorption-line surveys of gas in the halos of nearby spiral galaxies reveal that the circumgalactic medium (CGM) — which plays a fundamental role in shaping galaxy evolution — is metal-enriched, ionized, multiphase in nature, and ubiquitously present. We generate synthetic quasar absorption-line observations of the simulated CGM to trace cosmic gas flows in high-resolution cosmological zoom-in simulations of present-day spiral galaxies. Using these, we explore the physical origins of observed absorption lines, for low (e.g., LyA, MgII), intermediate (e.g., SiIII, CIV), and high (e.g., OVI) ions, and demonstrate that these simulations produce good agreement with observational results. In our simulations, low ions best trace the kinematics of gas inflows, while high ions best trace gas outflows: highly metal-enriched gas close to the galaxies originates from outflows, whereas accreted pre-enriched material dominates the enriched gas in the outer halo. We find that supplementing existing measurements with a recently proposed observational marker — the equivalent-width co-rotation fraction — may not only permit the tracing of gas accretion, recycling, and outflows, but potentially also distinguish between the various modes of gas accretion onto galaxies. Better characterisations of these gas flows, as enabled by new observational tracers for future measurements, will be necessary to understand the baryon cycle in evolving spiral galaxies, and, ultimately, the future evolution of these galaxies. |
