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, known as stellar streams. Sagittarius stream 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.

Recently, by mining Gaia data release 3 (DR3), researchers led by Dr. YANG Yong and Dr. ZHAO Jingkun from the National Astronomical Observatories of the Chinese Academy of Sciences (NAOC) have discovered a new stellar stream from dwarf galaxy in the Milky Way. This finding will enlarge the stream number originated from dwarf galaxy.

The results were published in The Astrophysical Journal Letters on March 1.

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

The researchers 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 exposed and was dubbed as Yangtze," said Dr. YANG.

Yangtze was proved not an artificial signal based on interstellar extinction and Gaia DR3 scanning pattern. It was measured to have a width of 1.9 degree and a length of 27 degree on the sky, with a distance of 9.12 kpc from the Sun, and its metallicity [Fe/H] was estimated to be -0.7 dex.

Fig. 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. (Image by YANG et al.)

The researchers also tried to understand whether Yangtze was associated with other known streams and globular clusters in the Milky Way. They found that the globular cluster Pal 1 was rather near to Yangtze in angular momentum and energy space, and the Anticenter Stream (ACS, a known stream) was almost on the orbit of Yangtze. These results suggest Yangtze may have a close connection with Pal 1 as well as ACS.

"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," said Dr. ZHAO.

Fig. 3 Left: globular clusters and Yangtze in angular momentum and energy space; Right: the orbit of Yangtze and trajectories of known streams. (Image by YANG et al.)