深入仙女座星系晕的天区：在 UNIONS 中发现飞马座 VII 矮星系
Deep in the Fields of the Andromeda Halo: Discovery of the Pegasus VII dwarf galaxy in UNIONS
AI总结：
研究利用 UNIONS 测光并结合 CFHT 与 Gemini-North 后续成像，发现并确认 M31 子群矮星系 Peg VII，测定其光度、尺寸、距离及拉伸形态。
摘要：
我们展示了新发现的矮星系 Pegasus VII（Peg VII），它是 M31 子星系群的成员，在 Ultraviolet Near-Infrared Optical Northern Survey 的 $ri$ 测光星表中被发现，并通过 Canada-France-Hawaii Telescope 和 Gemini-North Telescope 的后续成像得到确认。该系统的绝对 $V$ 波段星等为 $-5.7 \pm 0.2$ mag，物理半光半径为 $177^{+36}_{-34}$ pc，具有经动力学确认的银河系卫星矮星系的典型特征，并且比 M31 最延展的球状星团还要延展约 5 倍。Peg VII 与 M31 的三维间距为 $331^{+15}_{-4}$ kpc，且沿 M31 的投影方向具有显著拉伸（$ε\sim0.5$），这可能表明其曾经历潮汐相互作用；但为了更好地理解 Peg VII 的演化，还需要进一步研究其轨道、恒星形成历史以及星系中是否仍有气体残留。
英文摘要：
We present the newly discovered dwarf galaxy Pegasus VII (Peg VII), a member of the M31 sub-group which has been uncovered in the $ri$ photometric catalogs from the Ultraviolet Near-Infrared Optical Northern Survey and confirmed with follow-up imaging from both the Canada-France-Hawaii Telescope and the Gemini-North Telescope. This system has an absolute $V$-band magnitude of $-5.7 \pm 0.2$ mag and a physical half-light radius of $177^{+36}_{-34}$ pc, which is characteristic of dynamically-confirmed Milky Way satellite dwarf galaxies and about 5 times more extended than the most extended M31 globular clusters. Peg VII lies at a three-dimensional separation from M31 of $331^{+15}_{-4}$ kpc and a significant elongation ($ε\sim 0.5$) towards the projected direction of M31 could be indicative of a past tidal interaction, but additional investigation into the orbit, star formation history, and whether any gas remains in the galaxy is needed to better understand the evolution of Peg VII.
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