The Smith cloud: H i associated with the Sgr dwarf?
The Smith cloud: H i associated with the Sgr dwarf?
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史密斯云：H i 与人马座矮星有关吗？
DOI：
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发表时间：
1998
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通讯作者：
P. Maloney
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作者：
J. Bland;S. Veilleux;G. Cecil;M. Putman;B. K. Gibson;P. Maloney
在发射线[O III]15007、[N II]16548和Ha的两个位置观测到了史密斯高速云(VLSR o 98 km Sπ1)。[N II]和Ha剖面都显示了由于雷诺层而形成的明亮的核心，以及红色的机翼，其排放延伸到130千米的Sπ1。这是第一次同时探测到两条朝向高速云的发射线，使我们能够形成这些线轮廓的比率，作为当地静止标准(LSR)速度的函数。在这两个云层位置，我们看到了在云速度下的发射和雷诺层发射(VLSR<；0)之间的明显区别。雷诺层的[NIi]/Ha比(<；0：25)是典型的温电离介质。在云速度下，这一比率比相对于LSR的静止排放提高了3-4倍。从我们的数据得到了在[O III]处的中等深的上限(在3J时为0.12R)。如果是热年轻恒星的稀薄光致电离辐射，[NII]/Ha的高度增强、[O III]的未探测和弱的Ha发射(0.24-0.30R)表明Smith云距离太阳26 6 4kpc，银心半径为2 0 6 4kpc。这个值假设辐射来自一个光学厚度很厚的板条，电离光子的覆盖部分是统一的，其方向要么(A)平行于银河盘，要么(B)使从银盘接收的通量最大化。云的质量和大小估计为4〈10 6M(和6kpc)。我们讨论了与更大的SGR矮星的可能联系，它的银心半径为1662kpc，位于史密斯云358(12kpc)范围内。
ABSTRA C T The Smith high-velocity cloud (VLSR o 98 km s π1 ) has been observed at two locations in the emission lines [O III]l5007, [N II]l6548 and Ha. Both the [N II] and Ha profiles show bright cores due to the Reynolds layer, and red wings with emission extending to VLSR < 130 km s π1 . This is the first simultaneous detection of two emission lines towards a high-velocity cloud, allowing us to form the ratio of these line profiles as a function of local standard of rest (LSR) velocity. At both cloud positions, we see a clear distinction between emission at the cloud velocity, and the Reynolds layer emission (VLSR < 0). The [N II]/Ha ratio (<0:25) for the Reynolds layer is typical of the warm ionized medium. At the cloud velocity, this ratio is enhanced by a factor of 3‐4 compared to emission at rest with respect to the LSR. A moderately deep upper limit at [O III] (0.12R at 3j) was derived from our data. If the emission arises from dilute photoionization from hot young stars, the highly enhanced [N II]/Ha ratio, the [O III] non-detection and weak Ha emission (0.24‐0.30R) suggest that the Smith cloud is 26 6 4 kpc from the Sun, at a Galactocentric radius of 20 6 4 kpc. This value assumes that the emission arises from an optically thick slab, with a covering fraction of unity as seen by the ionizing photons, the orientation of which is either (a) parallel to the Galactic disc, or (b) such as to maximize the received flux from the disc. The estimated mass and size of the cloud are 4 〈 10 6 M( and 6 kpc. We discuss a possible association with the much larger Sgr dwarf, at a Galactocentric radius of 16 6 2 kpc, which lies within 358 (,12 kpc) of the Smith cloud.