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By analyzing the data from the DESI Legacy Imaging Survey, Chinese astronomers have investigated a globular cluster known as NGC 5634. Results of the new study, June 5 on the arXiv pre-print server, provide more insights into the structural and kinematical properties of this cluster.

Globular clusters (GCs) are collections of tightly gravitationally bound stars, containing hundreds of thousands, and sometimes millions of stars. Studies of GCs could help us advance our knowledge regarding the formation, history and evolution of early-type galaxies, given that the origin of these clusters seems to be closely linked to periods of intense star formation.

NGC 5634 is a globular cluster in the constellation Virgo, located some 82,200 light years away from the Earth. It is a relatively metal-poor and dynamically old GC assumed to originate from the Sagittarius dwarf spheroidal galaxy (Sgr dSph) and its associated stellar stream (Sgr stream).

In order to better understand the origin of NGC 5634, a team of astronomers led by Shouzhi Wang of the Beijing Normal University in China, has combed through the data from the DESI Legacy Imaging Survey to investigate the structure and kinematics of this cluster.

The researchers first redetermined the fundamental parameters of NGC 5634. They found that the cluster is about 12.8 billion years old, has a metallicity at a level of -1.8 dex, and its distance modulus is 17.0 mag.

The study found that NGC 5634 has a tidal radius of 8.35 arcminutes and its core radius is approximately 0.21 arcminutes. It turned out that the cluster has a radial velocity of -16.07 km/s and a relatively high concentration of stars, with a calculated concentration parameter of 1.6.

Furthermore, the researchers conducted a search for potential large-scale extra-tidal structures around NGC 5634. However, they found no evidence of extended extra-tidal features, such as tidal tails or extra-tidal stellar overdensities in this area.

When it comes to the orbit of NGC 5634, the astronomers found that it only briefly intersects with the Sgr stream and diverges significantly over long-term integrations. Therefore, the researchers concluded that there is currently insufficient evidence to support a strong association between NGC 5634 and the Sgr system.

The authors of the paper added that NGC 5634 exhibits a relatively shorter semi-major axis and smaller apocenter and pericenter distances compared to Sgr clusters.

"The Sgr GCs tend to have more distant pericenter and apocenter distributions, often accompanied by extended orbital ranges and relatively stable orbits. (...) These orbital characteristics [of NGC 5634] are more consistent with clusters associated with the Gaia-Sausage-Enceladus (GSE) or the Helmi streams," the scientists concluded.

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