Astronomers used the Atacama Large Millimeter/submillimeter Array (ALMA) to study NGC 602, a young open cluster in the Small Magellanic Cloud (SMC). The findings of the study, which were published on the arXiv pre-print server on August 29, provide important insights into the properties of this cluster, revealing that it underwent a sequential star formation process.
Open clusters (OCs) are groups of stars that are gravitationally bound to each other and formed from the same giant molecular cloud. More than 1,000 of them have been discovered so far in the Milky Way, and scientists are still looking for more in the hope of discovering a variety of these stellar groupings. Extending the list of known galactic open clusters and studying them in depth could be critical for improving our understanding of our galaxy’s formation and evolution.
NGC 602 is a young, bright, low-metallicity OC in SMC located 196,000 light years away. It is located in the “Wing” of the SMC, along with its associated HII region N90, which contains clouds of ionised atomic hydrogen. Because of their close proximity, NGC 602 and N90 provide an excellent opportunity to investigate star formation scenarios under conditions vastly different from the solar neighbourhood.
So, a team of astronomers led by Theo J. O’Neill of the University of Virginia used ALMA to investigate NGC 602/N90, focusing on the nature of dense gas in N90 and the evolution of the region.
The researchers wrote in their paper, “We present results from ALMA observations of molecular gas in the low-metallicity star-forming region NGC 602/N90.”
Over 100 molecular clumps were identified using carbon monoxide (CO) emission. The clumps are arranged around the rim of the region. The astronomers estimated the total molecular gas mass in N90 at 16,600 solar masses after studying the properties of these clumps.
The study discovered that clumps in N90 do not generally agree with expected trends in the size-linewidth-surface density space. Furthermore, they had larger velocity dispersions and lower surface densities than predicted by Galactic cloud relationships.
Furthermore, the findings indicate that intermediate-mass star formation has most likely occurred in the N90 region over the last one to two million years. In general, the recent star formation rate for NGC 602/N90 was calculated to be around 130 solar masses per year, and no strong evidence was found that NGC 602 has directly triggered star formation along the rim of N90.
The astronomers concluded that the properties of clumps in N90 revealed the region’s sequential star formation history. The results also show that star formation in N90 is not more efficient than star formation in higher-density, similarly massive solar-metallicity environments.