Are the most luminous supermassive black holes hidden in heavily obscured environments?

Artist’s illustration of the thick dust torus thought to surround supermassive black holes and their accretion disks. [ESA / V. Beckmann (NASA-GSFC)]

Active Galactic Nuclei (AGN) are galaxies with a rapidly growing supermassive black hole (SMBH) at their centre. A recent study, using both ground and space observations, suggests that many of the brightest SMBHs may be escaping our detection due to their heavily obscured environments. This draws a completely different picture compared to our current understanding of luminous AGN.

X-ray observations have shown that most obscured AGN become rarer with increasing luminosity. Based on the current paradigm, this is because luminous AGN erode the obscuring material, named dusty torus, that surrounds the SMBH, thus reducing its covering factor. Therefore, higher luminosity AGN should be rarely hidden from our view. A group of astronomers, used data from the Herschel Telescope and the XMM-Newton observatory and models that reproduce the geometrical covering factor of the dusty torus for 200 X-ray selected AGN. Their analysis revealed that obscured AGN are increasingly numerous at higher AGN luminosities. According to Dr. Silvia Mateos, who led the study, this result indicates that the impact of the enormous AGN accretion power on the geometry of the material surrounding the SMBH is not as strong as we thought. A large fraction of luminous, rapidly growing SMBHs are so deeply embedded that they are escaping X-ray detection.

If the result is confirmed the implications for the evolution of galaxies may be significant!



Publication: Mateos et al. 2017

Source: XMM-Newton