Understanding the growth of supermassive black holes (SMBHs) is an important aspect of understanding how the galaxies they live in grow and change over the lifetime of the Universe. Recent work on the general population of actively growing SMBHs (i.e., the active galactic nuclei or AGN) has found at the statistical relationship between the amount of gas obscuring our view towards the SMBH and the rate at which the SMBHs are growing is consistent with a scenario in which the radiation emitted by the AGN regulates and eventually removes the material that is both feeding the AGN and obscuring it.
Luminous and Ultraluminous Infrared Galaxies (U/LIRGs) in the nearby Universe are interacting and merging galaxy systems that show a mix of AGN and enhanced star formation. Curiously, there is some evidence that their SMBHs may be over-massive compared to the SMBHs of non-interacting galaxies of similar masses. When the SMBHs in ULIRGs are active, they also tend to be more heavily obscured. Does this mean the process that regulates the SMBH growth and obscuration is different? In “The Relationship Between Eddington Ratio and Column Density in U/LIRG AGN” (Nagarajan-Swenson+) we compiled the AGN in U/LIRGs with robust SMBH mass measurements and high-quality X-ray determinations of the growth rate and obscuring gas to compare with the general population of AGN described above. Ultimately the sample size of AGN in U/LIRGs was too small to suggest a difference in the growth process, but future studies based on additional SMBH mass measurements could test this.
The article has been published in the Research Notes of the American Astronomical Society (link above) and a preprint is available on arXiv.org.
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