Pegasus IV: Discovery and Spectroscopic Confirmation of an Ultra-faint Dwarf Galaxy in the Constellation Pegasus-猫眼课题宝

DOI：

10.3847/1538-4357/aca1c3

发表时间：

2022-03

期刊：

The Astrophysical Journal

影响因子：

通讯作者：

中科院分区：

其他

文献类型：

作者：

W. Cerny;J. Simon;T. Li;A. Drlica-Wagner;A. Pace;C. Martínez-Vázquez;A. Riley;B. Mutlu-Pakdil;S. Mau;P. Ferguson;D. Erkal;R. Munoz;C. Bom;J. Carlin;D. Carollo;Y. Choi;A. Ji;V. Manwadkar;D. Martinez-Delgado;A. Miller;N. Noël;J. Sakowska;D. Sand;G. Stringfellow;E. Tollerud;A. K. Vivas;J. Carballo-Bello;D. Hernandez-Lang;D. James;D. Nidever;J. L. N. Castellón;K. Olsen;A. Zenteno

我们报告了Pegasus IV的发现，这是一个超微弱的矮星系，在DECam局部体积探测调查处理的暗能量相机的档案数据中发现的。飞马四是一个紧密的、超微弱的恒星系统(R1/2=41−6+8pc；MV=−4.25±0.2mag)，位于90−6+4kpc的日心距离。根据用麦哲伦/iMACS观测到的7颗不变成员星的光谱，我们自信地解决了飞马4的速度色散，测得σv=3.3−1.1+1.7 KM S−1(剔除3个速度离群点后)，这意味着该系统的质量光比为M1/2/LV，1/2=16 7−99+224M⊙/L⊙。从信噪比最高的五颗恒星中，我们还测量到了[Fe/H]=−2.63−0.30+0.26Dex的系统金属丰度，使飞马四成为最缺乏金属的超暗矮星之一。我们试探性地解决了该系统的非零金属丰度色散。这些测量提供了强有力的证据，证明飞马四是一个以暗物质为主的矮星系，而不是一个星团。我们使用GAIA早期数据发布3，发现(μα*，μδ)=(0.33±0.07，−0.21±0.08)ma yr−1的数据来测量飞马四的自身运动。当结合我们测量的系统速度时，这个自身运动表明飞马四处于椭圆形的逆行轨道上，目前接近其轨道中心。最后，我们在Pegasus IV中发现了三颗潜在的天琴座RR变星，其中一颗候选恒星距离系统质心超过10个半光半径。另一个超暗矮星系的发现有力地表明，对银河系卫星的普查仍然不完整，即使在100kpc以内。

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 ( r1/2=41−6+8 pc; M V = −4.25 ± 0.2 mag) located at a heliocentric distance of 90−6+4kpc . Based on spectra of seven nonvariable member stars observed with Magellan/IMACS, we confidently resolve Pegasus IV’s velocity dispersion, measuring σv=3.3−1.1+1.7 km s−1 (after excluding three velocity outliers); this implies a mass-to-light ratio of M1/2/LV,1/2=167−99+224M⊙/L⊙ for the system. From the five stars with the highest signal-to-noise spectra, we also measure a systemic metallicity of [Fe/H] = −2.63−0.30+0.26 dex, making Pegasus IV one of the most metal-poor ultra-faint dwarfs. We tentatively resolve a nonzero 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 ± 0.07, −0.21 ± 0.08) 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 10 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.

Pegasus IV: Discovery and Spectroscopic Confirmation of an Ultra-faint Dwarf Galaxy in the Constellation Pegasus

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