2026ApJ...996L..30J

In dwarf galaxy models, outflows expel metal-enriched interstellar medium (ISM) into the circumgalactic medium (CGM) to reproduce their observed low metallicities, but measurements of dwarf CGM properties are scarce. We present a study of the CGM of an isolated dwarf at z = 0.5723 with a stellar mass of ≈5 × 10⁷M_⊙ and star formation rate (≈0.05 M_⊙ yr^–1) and ISM metallicity ([O/H] ≈ -0.9) consistent with the star-forming main sequence and mass-metallicity relation. A background quasar sight line with archival UV spectra probes the dwarf's CGM at a projected distance of 28 kpc, corresponding to approximately half of the estimated virial radius. The dwarf's CGM is detected in H I; intermediate metal ions of C III, O III, O IV, and S V; and kinematically broader, highly ionized O VI but is undetected in N IV and Ne VIII. Photoionization modeling of the intermediate ions indicates a modest volume filling factor (∼6% along the sight line or ∼2% globally) and a mass of ∼2 × 10⁸M_⊙, ∼4× higher than the dwarf's stellar mass but ∼10× less than the highly ionized CGM. The O VI kinematics are comparable to the dwarf's estimated virial velocity, suggesting that it is likely associated with cool, photoionized, and volume-filling CGM, with bulk motion or turbulence dominating over thermal pressure. The metallicity inferred for the intermediate ions is [O/H] = -0.6, but with low relative abundances of [C/O] = -0.6 and [N/O] < -1.0. The [N/O] is below levels expected of the dwarf's ISM but consistent with core-collapse supernova ejecta, suggesting that supernova-enriched gas escaped the dwarf without mixing significantly with ISM enriched in nitrogen from evolved, low-mass stars.