DDO 68-C: HST Confirms Yet Another Companion of the <i>Isolated</i> Dwarf Galaxy DDO 68

Abstract We present the results of deep Hubble Space Telescope photometry of the dwarf galaxy DDO 68-C, proposed as possibly associated with the isolated peculiar dwarf DDO 68. The new data resolve for the first time the stars of DDO 68-C down to well below the tip of the red giant branch (RGB), revealing a low-mass ( M ⋆ ≃ 1.5 × 10 7 M ⊙ ) star-forming galaxy with a backbone of old stars. By means of a fully homogeneous analysis and using the RGB tip as a standard candle, we find that DDO 68 and DDO 68-C lie at the same distance from us, within the uncertainties ( D = 12.6 ± 0.3 Mpc and D = 12.7 ± 0.4 Mpc, respectively), thus confirming that the two dwarfs are physically associated. While paired dwarf galaxies with a mutual projected distance similar to DDO 68 and DDO 68-C are not exceptional in the Lynx-Cancer void where they live, DDO 68 remains a unicum as, in addition to the newly confirmed companion, it records the evidence of at least two other satellites.