Artist’s conception of an active galaxy, with the black hole and accretion disk (central region). Around them is a gas and dust toroid, a typical structure of active nuclei. Credit: NASA / CXC / M.Weiss.
The active nuclei of galaxies are among the most energetic objects in the universe, and can continuously emit more than a hundred times the energy of all the stars in a galaxy like ours. Its brilliance is attributed to the existence of a supermassive black hole surrounded by a disk of matter that feeds it, but the phenomenon of nuclear activity still raises many questions. The instrument MEGARA, designed to solve hitherto unapproachable scientific problems, has just revealed new structures in the regions close to the active nucleus of NGC 7469.
NGC 7469, located about 200 million light years away – relatively close to astronomical scales -, it shows a high rate of star formation, which is attributed to a past interaction with its companion galaxy. It is a seyfert galaxy, a type of active galaxy that shows a very bright nucleus, product of the fall of material towards the supermassive black hole, which in this case has an estimated mass of about twelve million suns. For a black hole to be active there must be material to feed it and an efficient mechanism to transport the material to the core. Among these mechanisms are the discs, flattened structures that revolve around the black hole and whose material spirals towards the center, the bars, elongated structures that extend to both sides of the nucleus and that channel the gas from the arms of the spiral galaxies to the nucleus, or winds, very rapid flows of gas and dust capable of displacing large masses of material.
“Thanks to MEGARA we have been able to study the central region of NGC7469 with unprecedented resolution. We found that the ionized gas traces three components, two corresponding to disks that rotate simultaneously in the same plane, one finer than the other, and another that does not show rotation and is probably associated with the presence of winds, “he points out. Sara Cazzoli, researcher at the Institute of Astrophysics of Andalusia (IAA-CSIC) who heads the job.
“One of the big questions regarding active galaxies lies in the very origin of the activity. We know that almost all galaxies with masses similar to that of the Milky Way or larger have supermassive black holes in their nucleus, but some are in a state of torpor, such as SgrA *, the central black hole of our galaxy – he points out Isabel Márquez, researcher on IAA-CSIC who participates in the result. Studies with such high kinematic resolution are necessary to understand the phenomena related to the feeding and feedback of active galaxies, as well as the role that the different components play ”.
Galaxy NGC 7469 (above) and its companion, observed with the Hubble Space Telescope. Credit: NASA, ESA, the Hubble Heritage (STScI / AURA) -ESA / Hubble Collaboration, and A. Evans.
Knowing what happens in the central regions of active galaxies, or how gas moves in the different components, requires a state-of-the-art technological capacity.
The instrument MEGARA, designed by a consortium headed by the Complutense University of Madrid, in which the Institute of Astrophysics of Andalusia, It uses IFS technology –acronym in English of «integral field spectroscopy» -, which allows taking a thousand spectra per galaxy and obtaining a full 3D panoramic view of them. “Due to the brightness of the nuclear regions of the active galaxies, smaller telescopes were normally used for their study – he points out Armando Gil de Paz, researcher at the Complutense University of Madrid who participates in the work.
However, much of the information is found in gas clouds that differ from the rest: they move at high speeds and, due to these movements, they have their weak localized emission at frequencies different from the one that produces most of the gas in galaxies. . It is what are known as wings. Observing these wings requires the use of large telescopes and highly efficient instruments such as the Gran Telescopio Canarias and MEGARA, respectively ».
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