DDO68-C: HST confirms yet another companion of the isolated dwarf galaxy DDO 68

TL;DR

Deep HST observations confirm DDO 68-C as a low-mass, star-forming dwarf galaxy physically associated with DDO 68, providing insights into its satellite system within the Lynx-Cancer Void.

Contribution

First detailed stellar analysis of DDO 68-C confirming it as a companion galaxy and measuring its distance, expanding understanding of dwarf galaxy interactions in voids.

Findings

DDO 68-C is at the same distance as DDO 68, confirming companionship.

DDO 68 hosts at least two other satellite galaxies.

DDO 68-C is a low-mass, star-forming galaxy with old stellar populations.

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$_{*}$ $\sim$ 1.5 $\times$ 10$^7$ M$_{\odot}$) 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 $\pm$ 0.3 Mpc and D = 12.7 $\pm$ 0.4 Mpc, respectively), thus confirming that the two dwarfs are physically associated. While paired dwarf galaxies with 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.