摘要
We report two new sets of tidal debris nearby the Sagittarius （Sgr） tidal stream in the north Galactic cap （NGC） identified from the M giant stars in LAMOST DR2. The M giant stars located in the sky area of 210° 〈 A 〈 290°, and having a distance of 10-20 kpc and We/HI 〈 -0.75 show clear bimodality in their velocity distribution. We denote the two peaks as Vel-3＋83 for the one within a mean velocity of -3 km s^-1 with respect to that of the well observed Sgr leading tail at the same A and Ve1＋162＋26 for the other one with a mean velocity of 162km s^-1 with respect to the Sgr leading tail. Although the projected A-Vgsr relation of Vel-3＋83 is very similar to the Sgr leading tail, the opposite trend in the A-distance relation as compared to the Sgr leading tail suggests Vel-3＋83 has a different 3D direction of motion with any branch of the simulated Sgr tidal stream from Law ＆ Majewski. Therefore, we propose it is new tidal debris not related to the Sgr stream. Similarly, the other substructure Vel＋162＋26, which is the same one as the NGC group discovered by Chou et al., also moves toward a different direction with respect to the Sgr stream, implying that it may have a different origin than the Sgr tidal stream.
We report two new sets of tidal debris nearby the Sagittarius （Sgr） tidal stream in the north Galactic cap （NGC） identified from the M giant stars in LAMOST DR2. The M giant stars located in the sky area of 210° 〈 A 〈 290°, and having a distance of 10-20 kpc and We/HI 〈 -0.75 show clear bimodality in their velocity distribution. We denote the two peaks as Vel-3＋83 for the one within a mean velocity of -3 km s^-1 with respect to that of the well observed Sgr leading tail at the same A and Ve1＋162＋26 for the other one with a mean velocity of 162km s^-1 with respect to the Sgr leading tail. Although the projected A-Vgsr relation of Vel-3＋83 is very similar to the Sgr leading tail, the opposite trend in the A-distance relation as compared to the Sgr leading tail suggests Vel-3＋83 has a different 3D direction of motion with any branch of the simulated Sgr tidal stream from Law ＆ Majewski. Therefore, we propose it is new tidal debris not related to the Sgr stream. Similarly, the other substructure Vel＋162＋26, which is the same one as the NGC group discovered by Chou et al., also moves toward a different direction with respect to the Sgr stream, implying that it may have a different origin than the Sgr tidal stream.
基金
supported by the Strategic Priority Research Program “The Emergence of Cosmological Structures” of the Chinese Academy of Sciences(Grant No.XDB09000000)
the National Key Basic Research Program of China(2014CB845700)
the National Natural Science Foundation of China(NSFC,Grant Nos.11373032,11333003and U1231119)
the NSFC(Grant Nos.11173044 and 11503066)
the Shanghai Natural Science Foundation(14ZR1446900)
