New star-forming complexes discovered in galaxy NGC 4324

Using the Caucasus Mountain Observatory, Russian astronomers have investigated a nearby lenticular galaxy known as NGC 4324. They detected young star-forming complexes in the inner ring of this galaxy. The findings, presented October 14 on arXiv.org, could work on our insight about the formation and advancement of NGC 4324.

Located some 85 million light years away in the constellation Virgo, NGC 4324 (also known as UGC 07451) is an early-type lenticular galaxy about 66,000 light years in size. It has a stellar mass of some 56 billion solar masses, while its total mass is estimated to be at least 10 times greater.

Previous observations of NGC 4324 have found that it contains a significant amount of gas and have revealed its remarkable structure — a radiant blue ring of star formation implanted in a large-scale stellar disk typical for lenticular galaxies.

A team of astronomers from the Lomonosov Moscow State University in Russia, drove by Irina Proshina, inspected the pattern of star formation in the ring of NGC 4324. For this purpose, they used the 2.5-m telescope at the Caucasus Mountain Observatory. The study was supplemented by archival images from the SDSS, GALEX and WISE surveys.

"We chose to take full images of the galaxy NGC 4324 in narrow photometric bands focused on the Hα and [NII]λ6583 emission lines with the MaNGaL instrument — a mapper with a tunable filter.... The observations were carried out on April 17, 2018, with the 2.5-m telescope at the Caucasus Mountain Observatory," the researchers wrote in the paper.

All in all, the study detected 18 young star-forming complexes (clumps) with a mean size of about 1,600 light years. The largest clumps ended up having estimated stellar masses reaching 10 million solar masses.

https://documenter.getpostman.com/view/24044869/2s84LNUCgp

https://documenter.getpostman.com/view/24044869/2s84LNUY6C

https://documenter.getpostman.com/view/24046873/2s84LNUYF5

https://documenter.getpostman.com/view/24046873/2s84LNUYFA

https://documenter.getpostman.com/view/24046873/2s84LNUYKW

https://documenter.getpostman.com/view/24057197/2s84LRRrNn

https://documenter.getpostman.com/view/24057197/2s84LRSBAw

https://documenter.getpostman.com/view/24057197/2s84LRSBUg

https://documenter.getpostman.com/view/24057962/2s84LRSBnL

https://documenter.getpostman.com/view/24057962/2s84LRSBrh

https://documenter.getpostman.com/view/24057962/2s84LStV3f

https://documenter.getpostman.com/view/24068802/2s8YCYnvMd

https://documenter.getpostman.com/view/24068802/2s8YCYnvWK

https://documenter.getpostman.com/view/24068802/2s8YCYnvWU

The results suggest that the starbursts in these clumps have started as of late — within 10 million years. The astronomers explained that the stars that could be shaped during a previous starburst that occurred about 200 million years ago, cannot contribute now to the far-ultraviolet (FUV) luminosity having already detonated, or their luminosity peak has now shifted to the near-ultraviolet (NUV), leading to the observed dunk in the FUV of the clumps.

According to the research, there is a regularity in the distribution of star-forming complexes in the ring of NGC 4324. This suggests that the physical star formation mechanisms over local scales are the same in spiral and lenticular galaxies.

The researchers reasoned that their findings affirm the hypothesis about the possible feeding of the disk in NGC 4324 with gas through the infall of gas-rich satellite galaxies or giant clouds.

"Clumps are framed in the ring because of the gravitational instability, where star formation ignites. The subsequent star formation triggers in the gaseous ring are probably the shock waves from evolving complexes of massive OB stars — the first shaped clusters of young stars in the gaseous clumps. In addition, the infall of a satellite or a giant gas cloud onto the galactic disk can serve as a trigger of another starburst. Thus, the chain of 'gaseous clumps — star complexes' observed by us is a chain of the propagation of star formation both in space (in the ring) and on schedule," the authors of the paper explained.