Active supermassive black holes discovered in merging galaxies
A team of astronomers have found at least one supermassive black holes (SMBH) almost always becomes active and luminous by accreting a large amount of material in luminous, gas-rich, merging galaxies.
A team of astronomers at the National Astronomical Observatory of Japan (NAOJ), led by Dr. Masatoshi Imanishi, used Subaru Telescope's Infrared Camera and Spectrograph (IRCS) and its adaptive optics system to observe infrared luminous merging galaxies at the infrared K-band (a wavelength of 2.2 micrometers) and L'-band (a wavelength of 3.8 micrometers).
They used imaging data at these wavelengths to establish a method to differentiate the activities of deeply buried, active SMBHs from those of star formation. The radiative energy-generation efficiency from active, mass-accreting SMBHs is much higher than that of the nuclear fusion reactions inside stars.
An active SMBH generates a large amount of hot dust (several 100 Kelvins), which produces strong infrared L'-band radiation; the relative strengths of the infrared K- and L'-band emission distinguish the active SMBH from star-forming activity. Since dust extinction effects are small at these infrared wavelengths, the method can detect even deeply buried, active SMBHs, which are elusive in optical wavelengths.
Subaru Telescope's adaptive optics system enabled the team to obtain high spatial resolution images that allowed them to effectively investigate emission that originates in active SMBHs in the nuclear regions of galaxies by minimizing emission contamination from galaxy-wide, star-forming activity.
The team observed 29 infrared luminous gas-rich merging galaxies. Based on the relative strength of the infrared K- and L'-band emission at galaxy nuclei, they confirmed that at least one active SMBH occurs in every galaxy but one . This indicates that in gas-rich, merging galaxies, a large amount of material can accrete onto SMBHs, and many such SMBHs can show AGN activity.
(Posted on 29-01-2014)