2022ApJ...926L..33B

We present the discovery of neutral gas detected in both damped Lyα absorption (DLA) and H I 21 cm emission outside of the stellar body of a galaxy, the first such detection in the literature. A joint analysis between the Cosmic Ultraviolet Baryon Survey and the MeerKAT Absorption Line Survey reveals an H I bridge connecting two interacting dwarf galaxies (log (M _star/M _☉) = 8.5 ± 0.2) that host a z = 0.026 DLA with log[N(H I)/cm^–2] = 20.60 ± 0.05 toward the QSO J2339-5523 (z _QSO = 1.35). At impact parameters of d = 6 and 33 kpc, the dwarf galaxies have no companions more luminous than ≃0.05L _* within at least Δv = ±300 km s^–1 and d ≃ 350 kpc. The H I 21 cm emission is spatially coincident with the DLA at the 2σ-3σ level per spectral channel over several adjacent beams. However, H I 21 cm absorption is not detected against the radio-bright QSO; if the background UV and radio sources are spatially aligned, the gas is either warm or clumpy (with a spin temperature to covering factor ratio T _ s _/f c _ > 1880 K). Observations with VLT-MUSE demonstrate that the α-element abundance of the ionized interstellar medium (ISM) is consistent with the DLA (≃10% solar), suggesting that the neutral gas envelope is perturbed ISM gas. This study showcases the impact of dwarf-dwarf interactions on the physical and chemical state of neutral gas outside of star-forming regions. In the SKA era, joint UV and H I 21 cm analyses will be critical for connecting the cosmic neutral gas content to galaxy environments.