A Low-Latitude Halo Stream around the Milky Way
A Low-Latitude Halo Stream around the Milky Way
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DOI：
10.1086/374220
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发表时间：
2003-01
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影响因子：
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通讯作者：
B. Yanny;H. Newberg;E. Grebel;S. Kent;M. Odenkirchen;C. Rockosi;D. Schlegel;M. Subbarao;J. Brinkm
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作者：
B. Yanny;H. Newberg;E. Grebel;S. Kent;M. Odenkirchen;C. Rockosi;D. Schlegel;M. Subbarao;J. Brinkm
我们在银河系平面上提供了一个恒星环的证据，至少从l = 180°延伸到227°，关闭星等g ~ 19.5；这个环可以环绕银河系。我们推断，低银纬结构在银面以上距离银心的距离为R = 18±2 kpc，在银面以下采样区域的距离为R = 20±2 kpc。证据包括500个斯隆数字巡天（Sloan Digital Sky Survey）在平面30°范围内的恒星的光谱径向速度。在(l, b) =（198°，- 27°）处，与这种结构有关的恒星的速度色散为27 km s-1，在(l, b) =（225°，28°）处为22 km s-1，在(l, b) =（188°，24°）处为30 km s-1，在(l, b) =（182°，27°）处为30 km s-1。该结构以与银盘恒星相同的顺行方向旋转，但圆速度为110±25 km s-1。窄测量速度色散与幂律球或厚盘种群不一致。我们将这个结构中的速度色散与人马座矮星系潮汐流中的恒星的速度色散进行了比较，我们在(l, b) =（165°，- 55°）处测量了20 km s-1的速度色散。我们从[Fe/H] = -1.6的Ca II (K)线和关闭星的颜色估计了初步的金属丰度，色散指数为0.3，并注意到关闭星的颜色与椭球体的颜色一致。我们将我们的测量结果解释为一个被潮汐破坏的卫星的证据，其质量为2 × 107到5 × 108 M☉，环绕着银河系。
We present evidence for a ring of stars in the plane of the Milky Way, extending at least from l = 180° to 227° with turnoff magnitude g ~ 19.5; the ring could encircle the Galaxy. We infer that the low Galactic latitude structure is at a fairly constant distance of R = 18 ± 2 kpc from the Galactic center above the Galactic plane and has R = 20 ± 2 kpc in the region sampled below the Galactic plane. The evidence includes 500 Sloan Digital Sky Survey spectroscopic radial velocities of stars within 30° of the plane. The velocity dispersion of the stars associated with this structure is found to be 27 km s-1 at (l, b) = (198°, - 27°), 22 km s-1 at (l, b) = (225°, 28°), 30 km s-1 at (l, b) = (188°, 24°), and 30 km s-1 at (l, b) = (182°, 27°). The structure rotates in the same prograde direction as the Galactic disk stars but with a circular velocity of 110 ± 25 km s-1. The narrow measured velocity dispersion is inconsistent with power-law spheroid or thick-disk populations. We compare the velocity dispersion in this structure with the velocity dispersion of stars in the Sagittarius dwarf galaxy tidal stream, for which we measure a velocity dispersion of 20 km s-1 at (l, b) = (165°, - 55°). We estimate a preliminary metallicity from the Ca II (K) line and color of the turnoff stars of [Fe/H] = -1.6 with a dispersion of 0.3 dex and note that the turnoff color is consistent with that of the spheroid population. We interpret our measurements as evidence for a tidally disrupted satellite of 2 × 107 to 5 × 108 M☉ that rings the Galaxy.