Ultra-faint Milky Way Satellites Discovered in Carina, Phoenix, and Telescopium with DELVE Data Release 3

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Abstract We report the discovery of three Milky Way satellite candidates: Carina IV, Phoenix III, and DELVE 7, in the third data release of the DECam Local Volume Exploration survey (DELVE). The candidate systems were identified by cross-matching results from two independent search algorithms. All three are extremely faint systems composed of old, metal-poor stellar populations ( τ ≳ 10 Gyr, [Fe/H] ≲−1.4). Carina IV ( M V = −2.8; r 1/2 = 40 pc) and Phoenix III ( M V = −1.2; r 1/2 = 19 pc) have half-light radii that are consistent with the known population of dwarf galaxies, while DELVE 7 ( M V = 1.2; r 1/2 = 2 pc) is very compact and seems more likely to be a star cluster, though its nature remains ambiguous without spectroscopic follow-up. The Gaia proper motions of stars in Carina IV ( M ⋆ = 225 0 − 830 + 1180 M ⊙ ) indicate that it is unlikely to be associated with the LMC, while DECam CaHK photometry confirms that its member stars are metal poor. Phoenix III ( M ⋆ = 52 0 − 290 + 660 M ⊙ ) is the faintest known satellite in the extreme outer stellar halo ( D GC > 100 kpc), while DELVE 7 ( M ⋆ = 6 0 − 40 + 120 M ⊙ ) is the faintest known satellite with D GC > 20 kpc.

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