The Enigmatic (Almost) Dark Galaxy Coma P: Distance Measurement and Stellar Populations from HST Imaging
The Enigmatic (Almost) Dark Galaxy Coma P: Distance Measurement and Stellar Populations from HST Imaging
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DOI：
10.3847/1538-3881/aafb39
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发表时间：
2019-01
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通讯作者：
Samantha W. Brunker;K. McQuinn;J. Salzer;J. Cannon;S. Janowiecki;L. Leisman;K. Rhode;E. Adams;C. Ball;A. Dolphin;R. Giovanelli;M. Haynes
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作者：
Samantha W. Brunker;K. McQuinn;J. Salzer;J. Cannon;S. Janowiecki;L. Leisman;K. Rhode;E. Adams;C. Ball;A. Dolphin;R. Giovanelli;M. Haynes
我们展示了哈勃太空望远镜（HST）对低表面亮度（SB）星系彗发p的观测结果。这个星系最初是在阿雷西博遗产快速阿尔法H巡天中发现的，并被归类为一个（几乎）暗星系，因为它在现有的巡天数据（例如斯隆数字巡天）中没有表现出任何明显的光学对应。随后的WIYN pODI成像显示了位于H探测中心的超低SB恒星成分。我们使用HST图像生成了彗发p中存在的已分辨恒星群的深彩色星等图。我们清楚地发现了一个红色恒星序列，我们将其解释为红巨星分支，并用它来推断Mpc红巨星分支距离的一个尖端。新的距离大大低于先前的估计，表明后发星系P是一个极端矮星系。我们得到的恒星质量只有4.3 × 105 M⊙，这意味着彗发P的H -恒星质量比达到了81。我们对彗发P所在的星系环境进行了详细的分析。我们假设彗发P是在一个局部的空洞中形成的，并且在一个低密度的环境中度过了它生命的大部分时间。随着时间的推移，位于空洞壁上的星系的万有引力把它移到了边缘，在那里它最近与M64发生了一次“飞掠”相互作用。我们研究了彗发P在更远的距离上的可能性，并得出结论，现有数据最适合5.5 Mpc的距离。
We present Hubble Space Telescope (HST) observations of the low surface brightness (SB) galaxy Coma P. This system was first discovered in the Arecibo Legacy Fast ALFA H i survey and was cataloged as an (almost) dark galaxy because it did not exhibit any obvious optical counterpart in the available survey data (e.g., Sloan Digital Sky Survey). Subsequent WIYN pODI imaging revealed an ultra-low SB stellar component located at the center of the H i detection. We use the HST images to produce a deep color–magnitude diagram of the resolved stellar population present in Coma P. We clearly detect a red stellar sequence that we interpret to be a red giant branch and use it to infer a tip of the red giant branch distance of Mpc. The new distance is substantially lower than earlier estimates and shows that Coma P is an extreme dwarf galaxy. Our derived stellar mass is only 4.3 × 105 M⊙, meaning that Coma P has an extreme H i-to-stellar mass ratio of 81. We present a detailed analysis of the galaxy environment within which Coma P resides. We hypothesize that Coma P formed within a local void and has spent most of its lifetime in a low-density environment. Over time, the gravitational attraction of the galaxies located in the void wall has moved it to the edge, where it had a recent “fly-by” interaction with M64. We investigate the possibility that Coma P is at a farther distance and conclude that the available data are best fit by a distance of 5.5 Mpc.