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We present HI spectral-line imaging of the extremely metal-poor galaxy DDO68. This system has a nebular oxygen abundance of only 3% Z$_{\odot}$, makingit one of the most metal-deficient galaxies known in the local volume.Surprisingly, DDO 68 is a relatively massive and luminous galaxy for its metalcontent, making it a significant outlier in the mass-metallicity andluminosity-metallicity relationships. The origin of such a low oxygen abundancein DDO 68 presents a challenge for models of the chemical evolution ofgalaxies. One possible solution to this problem is the infall of pristineneutral gas, potentially initiated during a gravitational interaction. Usingarchival HI spectral-line imaging obtained with the Karl G. Jansky Very LargeArray, we have discovered a previously unknown companion of DDO 68. Thislow-mass (M$_{\rm HI}$ $=$ 2.8$\times$10$^{7}$ M$_{\odot}$), recentlystar-forming (SFR$_{\rm FUV}$ $=$ 1.4$\times$10$^{-3}$ M$_{\odot}$ yr$^{-1}$,SFR$_{\rm H\alpha}$ $<$ 7$\times$10$^{-5}$ M$_{\odot}$ yr$^{-1}$) companion hasthe same systemic velocity as DDO 68 (V$_{\rm sys}$ $=$ 506 km s$^{-1}$; D $=$12.74$\pm$0.27 Mpc) and is located at a projected distance of 42 kpc. New HImaps obtained with the 100m Robert C. Byrd Green Bank Telescope provideevidence that DDO 68 and this companion are gravitationally interacting at thepresent time. Low surface brightness HI gas forms a bridge between theseobjects.

Discovery of a Gas-Rich Companion to the Extremely Metal-Poor Galaxy DDO 68