It is well known that almost all isolated dwarf galaxies are actively forming stars. We report the discovery of dw1322m2053 (nicknamed Hedgehog), an isolated quiescent dwarf galaxy at a distance of 2.40 ± 0.15 Mpc with a stellar mass of M _⋆ ≈ 10^5.8 M _⊙. The distance is measured using surface brightness fluctuations with both Legacy Surveys and deep Magellan/IMACS imaging data. Hedgehog is 1.7 Mpc from the nearest galaxy group, Centaurus A, and has no neighboring galaxies within 1 Mpc, making it one of the most isolated quiescent dwarf galaxies at this stellar mass. It has a red optical color and early-type morphology and shows no UV emission. This indicates that Hedgehog has an old stellar population and no ongoing star formation. Compared with other quiescent dwarfs in the Local Group and Local Volume, Hedgehog appears smaller in size for its luminosity but is consistent with the mass–size relations. Hedgehog might be a backsplash galaxy from the Centaurus A group, but it could also have been quenched in the field by ram pressure stripping in the cosmic web, reionization, or internal processes such as supernova and stellar feedback. Future observations are needed to fully unveil its formation, history, and quenching mechanisms.

中文翻译：

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刺猬：一个孤立的静止矮星系，分辨率为 2.4 Mpc


众所周知，几乎所有孤立的矮星系都在积极形成恒星。我们报道了 dw1322m2053（昵称 Hedgehog）的发现，这是一个孤立的静止矮星系，距离为 2.40 ± 0.15 Mpc，恒星质量为 M_⋆ ≈ 10^5.8M_⊙。该距离是使用 Legacy Surveys 和深度 Magellan/IMACS 成像数据的表面亮度波动来测量的。刺猬距离最近的星系群半人马座 A 1.7 Mpc，并且在 1 Mpc 以内没有相邻星系，使其成为这个恒星质量中最孤立的静止矮星系之一。它具有红色的光学颜色和早期型形态，没有紫外线发射。这表明 Hedgehog 有一个古老的恒星种群，没有正在进行的恒星形成。与局部组和局部体积中的其他静止矮星相比，Hedgehog 的光度看起来更小，但与质量-大小关系一致。刺猬可能是来自半人马座 A 群的后挡星系，但它也可能在场中被宇宙网中的冲压压力剥离、再电离或超新星和恒星反馈等内部过程淬灭。需要进一步的观测来全面揭示它的形成、历史和淬灭机制。