We report the discovery of a ring-like cluster complex in the starburst galaxy NGC 2146 .
The Ruby Ring , so named due to its appearance , shows a clear ring-like distribution of star clusters around a central object .
It is located in one of the tidal streams which surround the galaxy .
NGC 2146 is part of the Snapshot Hubble U -band Cluster Survey ( SHUCS ) .
The WFC3/F336W data has added critical information to the available archival Hubble Space Telescope imaging set of NGC 2146 , allowing us to determine ages , masses , and extinctions of the clusters in the Ruby Ring .
These properties have then been used to investigate the formation of this extraordinary system .
We find evidence of a spatial and temporal correlation between the central cluster and the clusters in the ring .
The latter are about 4 Myr younger than the central cluster , which has an age of 7 Myr .
This result is supported by the H \alpha emission which is strongly coincident with the ring , and weaker at the position of the central cluster .
From the derived total H \alpha luminosity of the system we constrain the star formation rate density to be quite high ( \Sigma _ { \textnormal { SFR } } = 0.47 M _ { \odot } /yr/kpc ^ { 2 } ) .
The Ruby Ring is the product of an intense and localised burst of star formation , similar to the extended cluster complexes observed in M 51 and the Antennae , but more impressive because is quite isolated .
The central cluster contains only 5 % of the total stellar mass in the clusters that are determined within the complex .
The ring-like morphology , the age spread , and the mass ratio support a triggering formation scenario for this complex .
We discuss the formation of the Ruby Ring in a ” collect & collapse ” framework .
The predictions made by this model agree quite well with the estimated bubble radius and expansion velocity produced by the feedback from the central cluster , making the Ruby Ring an interesting case of triggered star formation .