Discovery of a damped Ly$\alpha$ absorber originating in a spectacular interacting dwarf galaxy pair at $z=0.026$

Abstract

We present the discovery of neutral gas detected in both damped Ly$\alpha$ absorption (DLA) and HI 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 HI bridge connecting two interacting dwarf galaxies (log$(M_{\text{star}}/{\text{M}}_{\odot })=8.5\pm 0.2$) that host a $z=0.026$ DLA with log[$N$(HI)/cm${}^{-2}$]$=20.60\pm 0.05$ toward the QSO J2339-5523 ($z_{\text{QSO}}=1.35$). At impact parameters of $d=6$ and $33$ kpc, the dwarf galaxies have no companions more luminous than $\approx 0.05L_{\ast }$ within at least $\Delta v=\pm 300$ km s${}^{-1}$ and $d\approx 350$ kpc. HI 21-cm emission is spatially coincident with the DLA at the 2-3$\sigma$ level per spectral channel over several adjacent beams. However, HI 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 spin temperature to covering factor ratio $T_s/f_c>1880$ K). VLT-MUSE observations demonstrate that the $\alpha$-element abundance of the ionized ISM is consistent with the DLA ($\approx 10$% 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 HI 21-cm analyses will be critical for connecting the cosmic neutral gas content to galaxy environments.

arXiv commentAccepted for publication in ApJL. 16 pages, 4 figures, 2 tables

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