论文标题
Pegasus IV：发现和光谱证实星座上的超品种矮人星系
Pegasus IV: Discovery and Spectroscopic Confirmation of an Ultra-Faint Dwarf Galaxy in the Constellation Pegasus
论文作者
论文摘要
我们报告了发现Pegasus IV的发现，这是一种在DECAM Local Volume Exploration调查中处理的档案数据中发现的超生物矮人的银河系。 Pegasus IV是一个紧凑的超物质恒星系统（$ r_ {1/2} = 41^{+8} _ { - 6} $ pc; $ m_v = -4.25 \ pm 0.2 $ 0.2 $ mag），位于$ 90^{+4} {+4} _ {+4} _ { - 6} $ { - 6} $ kpc的地震距离为$ 90^{+4}。基于与麦哲伦/iMac观察到的七个不可变化的成员明星的光谱，我们自信地解决Pegasus IV的速度分散，测量$σ_{v} = 3.3^{+1.7} _ { - 1.1} _ { - 1.1}}这意味着$ m_ {1/2}/l_ {v，1/2} = 167^{+224} _ { - 99} m _ {\ odot}/l _ {\ odot} $用于系统的系统。从具有最高信噪光谱的五颗星中，我们还测量了$ \ rm [fe/h] = -2.67^{+0.25} _ { - 0.29} $ dex的全身金属性，使Pegasus IV成为最高金属贫困的Ultra-faint Dwarfs之一。我们暂时解决该系统的非零金属性分散剂。这些测量值提供了有力的证据，表明Pegasus IV是一个由黑暗的矮人星系，而不是星团。我们使用Gaia早期数据版本3的数据测量Pegasus IV的适当运动，发现（$μ__{α*}，μ_δ）=（0.33 \ pm 0.07，-0.21 \ pm 0.08）\ text {mas yr}^{ - 1} $。当与我们测量的全身速度结合使用时，这种适当的运动表明Pegasus IV位于椭圆形的逆行轨道上，目前在其轨道式启动器附近。最后，我们确定了Pegasus IV内的三颗潜在的RR Lyrae变量恒星，其中包括一个距系统质心超过十半灯半径的候选成员。发现另一个超生物的矮人星系的发现强烈表明，即使在100 kpc之内，银河系的人口普查仍然不完整。
We report the discovery of Pegasus IV, an ultra-faint dwarf galaxy found in archival data from the Dark Energy Camera processed by the DECam Local Volume Exploration Survey. Pegasus IV is a compact, ultra-faint stellar system ($r_{1/2} = 41^{+8}_{-6}$ pc; $M_V = -4.25 \pm 0.2$ mag) located at a heliocentric distance of $90^{+4}_{-6}$ kpc. Based on spectra of seven non-variable member stars observed with Magellan/IMACS, we confidently resolve Pegasus IV's velocity dispersion, measuring $σ_{v} = 3.3^{+1.7}_{-1.1} \text{ km s}^{-1}$ (after excluding three velocity outliers); this implies a mass-to-light ratio of $M_{1/2}/L_{V,1/2} = 167^{+224}_{-99} M_{\odot}/L_{\odot}$ for the system. From the five stars with the highest signal-to-noise spectra, we also measure a systemic metallicity of $\rm [Fe/H] = -2.67^{+0.25}_{-0.29}$ dex, making Pegasus IV one of the most metal-poor ultra-faint dwarfs. We tentatively resolve a non-zero metallicity dispersion for the system. These measurements provide strong evidence that Pegasus IV is a dark-matter-dominated dwarf galaxy, rather than a star cluster. We measure Pegasus IV's proper motion using data from Gaia Early Data Release 3, finding ($μ_{α*}, μ_δ) = (0.33\pm 0.07, -0.21 \pm 0.08) \text{ mas yr}^{-1}$. When combined with our measured systemic velocity, this proper motion suggests that Pegasus IV is on an elliptical, retrograde orbit, and is currently near its orbital apocenter. Lastly, we identify three potential RR Lyrae variable stars within Pegasus IV, including one candidate member located more than ten half-light radii away from the system's centroid. The discovery of yet another ultra-faint dwarf galaxy strongly suggests that the census of Milky Way satellites is still incomplete, even within 100 kpc.
