The violent heart of galaxies exposed
The most massive black holes in our universe are encircled by thick discs of dust and gas. This torus-shaped material feeds and nourishes the growing black holes hidden inside that could not be seen through. Until recently, telescopes were not able to penetrate some of these tori. However, with the 10.4-m Great Canary Telescope (GCT), astronomers were able to observe light from such dense dust clouds. Within the EU-funded project FEEDING & HIDING AGN (Feeding and hiding the monster: Triggering and obscuring the central engine of active galaxies), they pinpointed and resolved the sources of infrared emission. Specifically, astronomers used both mid- and far-infrared data obtained with the instrument CanariCam. The FEEDING & HIDING AGN survey peered deep into more than 100 active galactic nuclei (AGN) and covered a broad range of activity levels and luminosities. The astronomers then combined GCT data with observations from the Herschel Space Observatory to confirm that AGN of different luminosities are triggered by different mechanisms. Luminous AGN were found to underlie galaxy interactions, while disc instabilities fed low-luminosity AGN. Unveiling AGN hidden behind ultra-thick tori did more than just resolve the long-standing issue of AGN-related outflow in dense molecular gas. It provided a rare opportunity to see how nearby faint galaxies could bombard them with material, helping drive their high star formation rates. FEEDING & HIDING AGN results offer support to the AGN unified model, according to which they are powered by centrally located supermassive black holes. Variations observed in the AGN properties are thought to be related to the line of sight astronomers have into the heart of galaxies.
Keywords
Galaxies, black holes, Great Canary Telescope, FEEDING & HIDING AGN, active galactic nuclei
