Tracing Inflows and Outflows with Absorption Lines in Circumgalactic Gas

We examine how HI and metal absorption lines within low-redshift galaxy halos trace the dynamical state of circumgalactic gas, using cosmological hydrodynamic simula-tions that include a well-vetted heuristic model for galactic outflows. We categorize inflowing, outflowing, and ambient gas based on its history and fate as tracked in our simulation. Following our earlier work showing that the ionisation level of absorbers was a primary factor in determining the physical conditions of absorbing gas, we show here that it is also a governing factor for its dynamical state. Low-ionisation metal absorbers (e.g. Mg ii) tend to arise in gas that will fall onto galaxies within several Gyr, while high-ionisation metal absorbers (e.g. Ovi) generally trace material that was deposited by outflows many Gyr ago. Inflowing gas is dominated by enriched ma-terial that was previously ejected in an outflow, hence accretion at low redshifts is typically substantially enriched. Recycling wind material is preferentially found closer to galaxies, and is more dominant in lower-mass halos since high-mass halos have more hot gas that is able to support itself against infall. Low-mass halos also tend to re-ejec