Astronomers from Radboud University in the Netherlands and abroad used the Keck Observatory to undertake spectroscopic investigations of NGC 1569-B, a young massive cluster. The results of the observational effort, which were published on the arXiv pre-print service on September 23, provide vital insights into the chemical makeup of this cluster. Young massive clusters (YMCs) are dense collections of young stars that serve as the basic building blocks of galaxies. The study of their chemical makeup might give vital information on stellar populations.
NGC 1569-B is a YMC in the dwarf irregular galaxy NGC 1569, situated about 6,000 light years distant from Earth. It is estimated to be 15-25 million years old. NGC 1569-B has a mass of around 440,000 solar masses, making it more massive than any of the Milky Way's or Large Magellanic Cloud's young clusters (LMC). Such huge clusters are extremely unusual in our galaxy, and much more so in the Local Group. Anastasia Gvozdenko headed a team of astronomers that used the high-resolution echelle spectrometer (HIRES) on Mauna Kea's Keck I 10-m telescope to explore NGC 1569-B. The primary goal of their research was to conduct a comprehensive chemical abundance analysis of this cluster.
We performed a high-resolution IL [integrated-light] spectrum investigation of the YMC NGC 1569-B, the researchers said in the publication. This is the first extensive abundance investigation of this YMC performed throughout the whole optical wavelength range.
The observations revealed that NGC 1569-B is somewhat metal-poor, with a metallicity of 0.77. It displays the bulk of the iron-peak element abundance ratios found in Milky Way thick disk or LMC bar stars. It is worth noting that the cluster has a relatively high titanium abundance of about 0.49.
The data also show that NGC 1569-B has a significantly high barium-to-iron abundance ratio. This might be due to the input of big stars, although no evidence supporting this notion has been discovered. Scandium to iron was discovered to have an unusually high abundance ratio. Because the authors of the publication are unable to explain this result at this time, more research into the chemical composition of NGC 1569-B is needed to develop a credible theory.
To summarize the findings, the researchers stated that the chemical abundances of NGC 1569-B are similar to those of another YMC that has recently been studied, NGC 1705-1.
According to the researchers, the star populations of NGC 1569-B are similar to those of the YMC NGC 1705-1, which is located in a blue compact dwarf galaxy. Except for Sc and Ba, which are exceptionally super-solar in NGC 1569-B and higher than in any other YMC investigated thus far, the two YMCs agree on alpha elements and the bulk of iron-peak elements.
Journal Information: Anastasia Gvozdenko, Søren S. Larsen, Michael A. Beasley, Jean Brodie, Chemical composition of the young massive cluster NGC 1569-B. arXiv:2209.11779v1 [astro-ph.GA], arxiv.org/abs/2209.11779