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

UNSPECIFIED (2026) Ultra-faint Milky Way Satellites Discovered in Carina, Phoenix, and Telescopium with DELVE Data Release 3. The Astrophysical Journal, 1000 (1): 46. ISSN 0004-637X

Text (pdf.pdf)
pdf.pdf - Published Version
Available under License Creative Commons Attribution.
Download (5MB)

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 (MV = −2.8; r1/2 = 40 pc) and Phoenix III (MV = −1.2; r1/2 = 19 pc) have half-light radii that are consistent with the known population of dwarf galaxies, while DELVE 7 (MV = 1.2; r1/2 = 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⋆=2250−830+1180M⊙ ) 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⋆=520−290+660M⊙ ) is the faintest known satellite in the extreme outer stellar halo (DGC > 100 kpc), while DELVE 7 ( M⋆=60−40+120M⊙ ) is the faintest known satellite with DGC > 20 kpc.