2014ApJ...787L...1C

We present H I spectral-line imaging of the extremely metal-poor galaxy DDO 68. This system has a nebular oxygen abundance of only ∼3% Z_☉, making it one of the most metal-deficient galaxies known in the local volume. Surprisingly, DDO 68 is a relatively massive and luminous galaxy for its metal content, making it a significant outlier in the mass-metallicity and luminosity-metallicity relationships. The origin of such a low oxygen abundance in DDO 68 presents a challenge for models of the chemical evolution of galaxies. One possible solution to this problem is the infall of pristine neutral gas, potentially initiated during a gravitational interaction. Using archival H I spectral-line imaging obtained with the Karl G. Jansky Very Large Array, we have discovered a previously unknown companion of DDO 68. This low-mass (M_HI = 2.8x10⁷ M_☉), recently star-forming (SFR_FUV= 1.4x10^–3 M_☉/yr, SFR_Hα< 7x10^–5 M_☉/yr) companion has the same systemic velocity as DDO 68 (V_sys= 506 km/s; D = 12.74±0.27 Mpc) and is located at a projected distance of ∼42 kpc. New H I maps obtained with the 100 m Robert C. Byrd Green Bank Telescope provide evidence that DDO 68 and this companion are gravitationally interacting at the present time. Low surface brightness H I gas forms a bridge between these objects.