A recent image from the DESI Legacy Imaging Survey shows a mysterious globular cluster Whiting 1 in the Galactichalo. So who is Whiting 1 and why do we care?

Whiting 1 is a faint and young globular cluster embedded in the Sagittarius stream. It was originally reported as a globular cluster formed in situ within the galactic halo, however, its young age and moderately rich metallicity run counter to our common sense regarding typical galactic globular clusters.

An age-metallicity relationship as well as a kinematics comparable to those of the Sagittarius stream make Whiting 1 a member of a rare class of objects. Astronomers are more inclined to believe that Whiting 1 is a child of the Sagittarius dwarf galaxy.

In recent years, the fact that the Sagittarius dwarf galaxy can host globular clusters and contribute to the formation of the Galactichalo is firmly accepted. As for Whiting 1, it may have been a cluster born in the Sagittarius Dwarf Galaxy and immigrated to our Galaxy along the Sagittarius Stream by galactic accretion. It’s a good origin story, but the speculation needs to be confirmed.

The best way to explore the origin of Whiting 1 is to find a relationship between the cluster and the Sagittarius dwarf galaxy. In the past, studies were mainly devoted to comparing the parameters of the cluster to the Sagittarius dwarf galaxy, however, due to the lack of more in-depth data, there was no further progress for a long time.

Different from traditional studies, a recent study by Dr. NIE Jundan and his colleagues from the National Astronomical Observatories of the Chinese Academy of Sciences (NAOC) uses a new approach to explore the origin of Whiting 1: They start with the morphology of the cluster.

This result was published in The Astrophysical Journal.

“If Whiting 1 is indeed associated with the Sagittarius dwarf galaxy, its morphology should show a tentative spatial connection to its ancestor. But this requires extensive data because the cluster is very far from us,” said Dr NIE, first author of the study.

This research leverages the depth of DESI Legacy Imaging Survey data to explore potential connections. DESI Legacy Survey is one of the most in-depth image surveys of our new century. It can go deep enough to reach Whiting 1.

“With DESI, we can travel directly to the homeland of Whiting 1. This way, more members of a common bloodline can be discovered. With enough member stars, we can uncover the true face of this cluster,” said Dr NIE.

The search uses DESI data to filter out all possible Whiting 1 members and take a no-makeup family photo for them. The two tidal tails on both sides of the cluster are particularly eye-catching. Its shape and extent are direct evidence of Whiting 1’s association with the Sagittarius dwarf galaxy. This echoes the fact that Whiting 1 was a pre-existing globular cluster in the dwarf galaxy of Sagittarius, and later immigrated to our galactic halo with its parents.

The intriguing origin of Whiting 1 makes it a perfect example for studying galactic cluster formation, and this work provides further evidence that the dwarf galaxy can host globular clusters and help build the galactic halo.

“With data from future DESI spectra, we can better understand how all the children in Whiting 1 are playing in their backyards,” said co-author Dr. ZOU Hu, who is also a member of DESI. “We believe that at this time DESI can explore more than what we have now.”