Using the Circumgalactic H-alpha Spectrograph (CHαS), astronomers have made spectroscopic observations of a nearby active galaxy called Messier 77. They discovered a very extended structure of ionized gas around this galaxy. The finding was published in a research paper posted on the preprint server on August 22. arXiv and accepted for publication in The Astrophysical Journal.

Messier 77 (or M77 for short, also known as NGC 1068) is a barred spiral galaxy located about 47 million light-years away. It has an active galactic nucleus (AGN) that globally ionizes gas in its disk and halo. Messier 77 is the closest Seyfert galaxy of type 2 and is considered the prototype of this class. The diameter of the galaxy is estimated at 90,000 light-years and its mass is about 1 billion solar masses.

Recently, a team of astronomers led by Nicole Melso of the Steward Observatory in Tucson, Arizona, used CHαS on the Hilter 2.4-m telescope at the MDM Observatory in Arizona to take wide-field spectral photographs of Messier 77. The main goal of their observations was to study the distribution of ionized gas around this galaxy.

“We have performed a large-scale mapping of the ultralow surface brightness hydrogen-alpha emission lines around NGC 1068 using the newly commissioned Circumgalactic Hα Spectrograph (CHαS),” the researchers wrote.

Melso’s team identified extended emission around Messier 77, located beyond previously discovered filamentary structures in this galaxy at the edge of the CHαS field of view. This emission turned out to be in the galactic halo at an angular distance of about 292 arcseconds from the galactic center.

Astronomers named the newly discovered extended structure of ionized gas the “band.” Based on the CHαS observations, the band was determined to have a projected physical radius of about 66,500 light-years.

The collected data indicate that the band gas is not associated with any galactic structure or known tidal forces in the halo of Messier 77. Moreover, unlike filaments closer to the galaxy, the band gas is slightly deviated from the flow axis of the central jet.

The results also suggest that the Ribbon Gas most likely consists of young stars embedded in warm, line-emitting gas that is ionized by a mix of processes. However, further studies of this gas are needed to shed more light on its origin and composition.

“Further observations of the neutral atomic and molecular gas in the filament and band structures will be important to understand the origin of the band gas in the circumgalactic medium of NGC 1068, the amount of gas available for star formation, and the extent of AGN-induced star formation in these regions,” the authors of the article conclude.

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