AN EXTENDED VIEW OF THE PISCES OVERDENSITY FROM THE SCUSS SURVEY
AN EXTENDED VIEW OF THE PISCES OVERDENSITY FROM THE SCUSS SURVEY
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DOI：
10.1088/0004-637x/810/2/153
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发表时间：
2015-08
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影响因子：
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通讯作者：
J. Nie;M. Smith;V. Belokurov;X. Fan;Z. Fan;M. Irwin;Z. Jiang;Y. Jing;Sergey E. Koposov;M. Lesser;J. Ma;S. Shen;J. Wang;Z. Wu;T. Zhang;X. Zhou;Z. Zhou;H. Zou
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作者：
J. Nie;M. Smith;V. Belokurov;X. Fan;Z. Fan;M. Irwin;Z. Jiang;Y. Jing;Sergey E. Koposov;M. Lesser;J. Ma;S. Shen;J. Wang;Z. Wu;T. Zhang;X. Zhou;Z. Zhou;H. Zou
南银帽u波段巡天（SCUSS）是一个u波段测光测量，覆盖南银帽约4000平方度，深度达23等。通过比斯隆数字巡天（SDSS）单历元u数据深1.5等，SCUSS能够探测更大体积的外晕，即，利用SCUSS数据，蓝色水平分支（BHB）星可以追踪银河系外晕100-150千秒差距。利用这一优势，我们结合联合收割机SCUSS的u波段与SDSS DR 9 gri光度带，以确定BHB星和探索晕子结构。我们证实了双鱼座超密度的存在，这是一个结构的外晕（约80千秒差距），发现使用RR天琴座恒星。这是我们第一次能够确定它的空间范围，发现它似乎是一个清晰的距离梯度流的一部分。该溪流宽约15 °，沿沿着125 °延伸，由20-30个BHB组成，总显著性约为背景的6σ。假设我们已经探测到了整个星系流，并且前身星系已经完全分裂，那么BHB的数量表明，原始系统类似于一个较小的经典星系或一个较大的超暗矮星系。另一方面，如果祖先仍然存在，则可以通过根据流的距离梯度重建其轨道来寻找它。这张双鱼座高密度的新照片为这个有趣的系统的起源提供了新的线索。
The South Galactic Cap u-band Sky Survey (SCUSS) is a u-band photometric survey covering about 4000 square degrees of the South Galactic Cap, reaching depths of up to 23 mag. By extending around 1.5 mag deeper than the Sloan Digital Sky Survey (SDSS) single-epoch u data, SCUSS is able to probe a much larger volume of the outer halo, i.e., with SCUSS data blue horizontal branch (BHB) stars can trace the outer halo of the Milky Way as far as 100–150 kpc. Utilizing this advantage we combine the SCUSS u-band with the SDSS DR9 gri photometric bands to identify BHB stars and explore halo substructures. We confirm the existence of the Pisces overdensity, which is a structure in the outer halo (at around 80 kpc) that was discovered using RR Lyrae stars. For the first time we are able to determine its spatial extent, finding that it appears to be part of a stream with a clear distance gradient. The stream, which is ∼5° wide and stretches along ∼25°, consists of 20–30 BHBs with a total significance of around 6σ over the background. Assuming we have detected the entire stream and that the progenitor has fully disrupted, then the number of BHBs suggests that the original system was similar to a smaller classical or a larger ultra-faint dwarf galaxy. On the other hand, if the progenitor still exists, it can be hunted for by reconstructing its orbit from the distance gradient of the stream. This new picture of the Pisces overdensity sheds new light on the origin of this intriguing system.