深入研究DES矮星系候选者：鹤I和印度河II
A Deeper Look at DES Dwarf Galaxy Candidates: Grus I and Indus II
摘要：
我们提出了深$g$和$r$波段麦哲伦/Megacam测光的暗能量调查（DES）中发现的两个矮星系候选人，鹤I和印度河II（DES J2038-4609）。对于天鹤座I的情况，我们解决了主序星关闭（MSTO）和$\sim 2$马格它下面。MSTO可以看到在$g_0\sim 24$与$0.03$马格的光度不确定性。我们表明天鹤座I是一致的老，贫金属（$\sim 13.3$陀螺仪，[Fe/H] $\sim-1.9$）矮星系。我们使用这个深度、均匀、宽视场的数据集推导出Grus I的更新距离和结构参数。我们发现一个方位角平均半光半径大于2倍（$\sim 151^{+21}_{-31}$ pc; $\sim 4.^{\prime} 16^{+0.54}_{-0.74}$）和一个绝对的$V$ -带幅度$\sim-4.1$是$\sim 1$幅度比以前的研究更明亮。我们得到更新的距离，椭圆率和质心参数与其他研究的不确定性。虽然我们的光度测定的印度河二是$\sim 2-3$级深于DES Y1公开发布，我们发现没有连贯的恒星人口在其报告的位置。最初的探测位于DES Y2 Q1数据集中的一个不完整的天空区域，由于潜在的蓝色水平分支成员星而被标记。最佳拟合等时线参数与矮星系和球状星团的物理不一致。我们的结论是，印度河二号可能是一个假阳性，由于沿着视线的恒星排列的机会标记。
英文摘要：
We present deep $g$- and $r$-band Magellan/Megacam photometry of two dwarf galaxy candidates discovered in the Dark Energy Survey (DES), Grus I and Indus II (DES J2038-4609). For the case of Grus I, we resolved the main sequence turn-off (MSTO) and $\sim 2$ mags below it. The MSTO can be seen at $g_0\sim 24$ with a photometric uncertainty of $0.03$ mag. We show Grus I to be consistent with an old, metal-poor ($\sim 13.3$ Gyr, [Fe/H]$\sim-1.9$) dwarf galaxy. We derive updated distance and structural parameters for Grus I using this deep, uniform, wide-field data set. We find an azimuthally averaged half-light radius more than two times larger ($\sim 151^{+21}_{-31}$ pc; $\sim 4.^{\prime} 16^{+0.54}_{-0.74}$) and an absolute $V$-band magnitude $\sim-4.1$ that is $\sim 1$ magnitude brighter than previous studies. We obtain updated distance, ellipticity, and centroid parameters which are in agreement with other studies within uncertainties. Although our photometry of Indus II is $\sim 2-3$ magnitudes deeper than the DES Y1 Public release, we find no coherent stellar population at its reported location. The original detection was located in an incomplete region of sky in the DES Y2Q1 data set and was flagged due to potential blue horizontal branch member stars. The best fit isochrone parameters are physically inconsistent with both dwarf galaxies and globular clusters. We conclude that Indus II is likely a false-positive, flagged due to a chance alignment of stars along the line of sight.
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