The Milky Way increases its mass through merging low-mass dwarf galaxies. Some of dwarf galaxies will experience tidal force during orbiting around the Milky Way, and their member stars will be lost.

As a result, there will be tidal tails on the one side or on both sides of the dwarf galaxies, which are also known as stellar streams. Sagittarius stream (an artistic picture is shown in Figure 1) is the most typical and direct evidence of it. However, there are far more streams generated by globular clusters than those generated by dwarf galaxies in the Milky Way so far.

Figure 1: Artistic representation of the Sagittarius dwarf galaxy in its current approximation to the Milky Way. (Credit: Gabriel Pérez Díaz, SMM/IAC)

Recently, by mining Gaia data release 3 (DR3), a new stellar stream in the Milky Way was found by Drs. YANG Yong, ZHAO Jing-Kun et al. from the Stellar Abundances and Galactic Evolution Group of the National Astronomical Observatories of the Chinese Academy of Sciences (NAOC). The results have been published in The Astrophysical Journal Letters this March. This finding will enlarge the stream number originated from dwarf galaxy.

The authors developed an algorithm called Stream Scanner based on a matched filter method. This algorithm is designed for detecting streams by combining proper motions and photometry from Gaia. A new stream was successfully exposed which was dubbed as Yangtze.

The trajectory of Yangtze in R.A.-Dec. panel is shown with the red dashed line in the middle panel of Figure 2. The left and right panels show interstellar extinction and Gaia DR3 scanning pattern, to prove Yangtze is not an artificial signal. Yangtze is measured to have a width of 1.9 degree and a length of 27 degree on sky, with a distance of 9.12 kpc from the sun. Its metallicity [Fe/H] is estimated to be -0.7 dex.

Figure 2: The middle panel shows Yangtze location (red dashed line). The left and right ones show the interstellar extinction map and Gaia DR3 scanning pattern, respectively. (Credit: Yang et al.)

The authors also tried to understand whether Yangtze is associated with other known streams and globular clusters in the Milky Way. The left panel of Figure 3 shows that the globular cluster Pal 1 is rather near to Yangtze in angular momentum and energy space. The right panel shows The Anticenter Stream (ACS, a known stream) is almost on the orbit of Yangtze. Those results suggest Yangtze may have a close connection with Pal 1 as well as ACS.

Figure 3: Left: globular clusters and Yangtze in angular momentum and energy space; Right: the orbit of Yangtze and trajectories of known streams. (Credit: Yang et al.)

Dwarf galaxy debris streams are key materials to reveal the Galactic structure and evolution. Yangtze should be helpful in studying the merger history of the Milky Way.

This paper was published on March 1, 2023 at https://iopscience.iop.org/article/10.3847/2041-8213/acbb5c

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