New tidal debris nearby the Sagittarius leading tail from the LAMOST DR2 M giant stars

TL;DR

This paper identifies two new tidal debris structures near the Sagittarius stream using LAMOST DR2 M giant stars, revealing their distinct kinematic and spatial properties, and suggesting they are separate from the Sgr stream.

Contribution

The study discovers and characterizes two new tidal debris structures near the Sagittarius stream, showing they are likely separate entities based on velocity and distance relations.

Findings

Two new tidal debris structures identified near Sgr stream.

Vel-3+83 has distinct 3D motion from Sgr stream.

Vel+162+26 likely has a different origin from Sgr stream.

Abstract

We report two new tidal debris nearby the Sagittarius (Sgr) tidal stream in the north Galactic cap identified from the M giant stars in LAMOST DR2 data. The M giant stars with sky area of $210^\circ<$\Lambda$<290^\circ$, distance of 10--20kpc, and [Fe/H]$<-0.75$ show clear bimodality in velocity distribution. We denote the two peaks as Vel-3+83 for the one within mean velocity of -3kms$^{-1}$ with respect to that of the well observed Sgr leading tail at the same $\Lambda$ and Vel+162+26 for the other one with mean velocity of 162kms$^{-1}$ with respect to the Sgr leading tail. Although the projected $\Lambda$--$V_{gar}$ relation of Vel-3+83 is very similar to the Sgr leading tail, the opposite trend in $\Lambda$--distance relation against 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 to be a new tidal debris not related to the Sgr stream. Similarly, the another 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 the Sgr stream, implying that it may have different origin with the Sgr tidal stream.