牧夫座II矮椭球的光谱确认
A spectroscopic confirmation of the Bootes II dwarf spheroidal
摘要：
我们提出了一套新的光度和光谱数据暗淡的牧夫座II矮球状星系候选人。我们用INT/WFC获得的深度测光表明，距离为46千秒差距，半光半径为4.0弧分（56秒差距），与以前的估计一致。后续的光谱与双子座/GMOS仪器获得径向速度和金属丰度。虽然我们的大多数目标涵盖了广泛的速度和金属丰度范围，但我们发现了五颗速度和金属丰度非常相似的恒星，并且它们都与银河系可能的红巨星分支的颜色和大小兼容。我们将这些解释为Bootes II系统的光谱检测。这些恒星的平均速度为-117 km/s，速度色散为（10.5+-7.4）km/s，平均[Fe/H]为-1.79 dex，色散为0.14 dex。在这个金属丰度下，Boo II与更明亮的矮星系的恒星-质量-金属丰度关系并不一致。再加上我们的距离估计，它的高负系统速度排除了与其投影邻居Bootes I矮球体的任何物理联系，其速度约为+100 km/s。牧夫座II的速度和距离与人马座主旋臂的速度和距离一致，它穿过天空的这一区域，因此牧夫座II可能是一个与人马座流有关的恒星系统。最后，我们注意到牧夫座II的性质与先前更大，更明亮的dSph星系的幸存遗迹是一致的。
英文摘要：
We present a new suite of photometric and spectroscopic data for the faint Bootes II dwarf spheroidal galaxy candidate. Our deep photometry, obtained with the INT/WFC, suggests a distance of 46 kpc and a small half-light radius of 4.0 arcmin (56 pc), consistent with previous estimates. Follow-up spectroscopy obtained with the Gemini/GMOS instrument yielded radial velocities and metallicities. While the majority of our targets covers a broad range in velocities and metallicities, we find five stars which share very similar velocities and metallicities and which are all compatible with the colors and magnitudes of the galaxy's likely red giant branch. We interpret these as a spectroscopic detection of the Bootes II system. These stars have a mean velocity of -117 km/s, a velocity dispersion of (10.5+-7.4) km/s and a mean [Fe/H] of -1.79 dex, with a dispersion of 0.14 dex. At this metallicity, Boo II is not consistent with the stellar-mass-metallicity relation for the more luminous dwarf galaxies. Coupled with our distance estimate, its high negative systemic velocity rules out any physical connection with its projected neighbor, the Bootes I dwarf spheroidal, which has a velocity of ~+100 km/s. The velocity and distance of Bootes II coincide with those of the leading arm of Sagittarius, which passes through this region of the sky, so that it is possible that Bootes II may be a stellar system associated with the Sagittarius stream. Finally, we note that the properties of Bootes II are consistent with being the surviving remnant of a previously larger and more luminous dSph galaxy.
机构、总结、中文摘要均由AI分析而来，可能存在错误，请以论文正文为准。
