Using the 6-meter telescope of the Special Astrophysical Observatory (SAO) and the 2.5-meter telescope of the Caucasus Mountains Observatory (CMO), Russian astronomers have observed a giant galaxy known as NGC 2655. Observation campaign results, presented January 12 on the arXiv Preprint server, sheds more light on the kinetics and origin of ionized gas in this galaxy.
At a distance of about 79.5 million light yearsNGC 2655 is a giant disk galaxy in the constellation Camelopardalis. NGC 2655’s disk has a diameter of about 195,000 light-years, while the galaxy’s star mass is estimated to be about 200 billion solar masses.
NGC 2655 is the brightest member of the NGC 2655 group of seven galaxies brighter than −15 mag, all of the delayed type. This indicates that the entire gas content of NGC 2655 may result from accretion of dwarfs surrounding the central galaxy.
The gas content of NGC 2655 caught the attention of a team of astronomers led by Olga Silchenko of Lomonosov Moscow State University in Russia. They searched this galaxy using SAO and CMO.
“NGC 2655 is a test case for a very steep rotation of gas in the absence of any star formation in the gas-rich S0, which is of particular interest to us…. We have made some additional observations and are now ready to dig into the details of how and when the gas reached NGC 2,655,” the researchers wrote in the paper.
Observations found that NGC 2655 has two exponential disks. These discs have different scale lengths and also different orientations of the equal major axis. Overall, the results indicate that the inner and outer rotation axes of NGC 2655’s stellar disk are tilted to each other. Therefore, astronomers have concluded that NGC 2655 is a multiple rotating galaxy.
Moreover, the study found that the orientations of the massive disk of neutral hydrogen and the outer stellar disk in NGC 2655 match each other spatially and kinematically. The astronomers added that the outer gaseous disk is located inside the outer stellar disk, and even the current star formation is happening somewhere in it.
According to the paper, the data obtained confirm that a minor merger has occurred in NGC 2655, which previous studies have suggested. The researchers hypothesize that a small satellite galaxy struck the central part of NGC 2655 almost vertically about 10 million years ago.
“Apparently, a companion fell on the galaxy almost perpendicularly, and now, two kilometers from the center, we observe the remnants of a destroyed companion in the form of a circular ring – the image is very similar to the sagittal dwarf torn apart by the Milky Way,” the authors explain.
However, they point out that in the case of NGC 2655, there was a lot of gas in the compact companion. In an attempt to explain the origin of ionized gas in NGC 2655, scientists have concluded that vertically falling galactic companion gas hit the gaseous disk of the galaxy in a state of uniform rotation. This collision created a shock wave that stirred gas in the polar ring and ran outward through the large galactic disk of gas.
Olga K. Sil’chenko et al, Kinematics and Origin of Gas in the Disk Galaxy NGC 2655, arXiv (2023). doi: 10.48550/arxiv.2301.05326
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