Astronomers detect expanse of ionized gas around Messier 77

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

Messier 77 (or M77 for short, also known as NGC 1068) is a barred spiral galaxy located about 47 million light-years away. It harbors an active galactic nucleus (AGN), which is ionizing the gas in its disk and halo. Messier 77 is the nearest type 2 Seyfert galaxy and is considered a prototype of this class. The galaxy is estimated to be 90,000 light-years in diameter and has a mass of 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 2.4-m Hilter telescope at the MDM Observatory in Arizona to perform wide-field spectral imaging of Messier 77. The main goal of their observations was to inspect the distribution of ionized gas around this galaxy.

“We have mapped the wide-field, very low surface brightness hydrogen-alpha emission line around NGC 1068 with the recently commissioned Circumgalactic Hα Spectrograph (CHαS),” the researchers wrote.

Melso’s team identified an extended emission around Messier 77, located beyond the filamentary structures previously detected in this galaxy, towards the edge of CHαS’s 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 have dubbed the new extended structure of ionized gas “the ribbon.” Based on CHαS observations, the ribbon was found to have a projected physical radius of about 66,500 light-years.

The collected data indicate that the ribbon gas is not associated with any galactic structure or tidal features known in the halo of Messier 77. Furthermore, unlike what is observed in filaments closer to the galaxy, the ribbon gas is slightly misaligned with the current axis of the central jet.

The results also suggest that the gas in the ribbon is most likely composed of young stars embedded in hot gas emitting ionized lines by a mixture of processes. However, further research into this gas is needed to better understand its origin and composition.

“Follow-up observations of neutral atomic and molecular gas in filamentary and ribbon structures will be important for understanding the origin of the ribbon gas in the circumgalactic medium of NGC 1068, the amount of gas available for star formation, and the level of AGN-induced star formation occurring in these regions,” the authors of the paper conclude.

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