The redshift evolution of major merger triggering of luminous AGN: a slight enhancement at z$\sim$2

Abstract

Active galactic nuclei (AGN), particularly the most luminous AGN, are commonly assumed to be triggered through major mergers, however observational evidence for this scenario is mixed. To investigate any influence of galaxy mergers on AGN triggering and luminosities through cosmic time, we present a sample of 106 luminous X-ray selected type 1 AGN from the COSMOS survey. These AGN occupy a large redshift range (0.5 < z < 2.2) and two orders of magnitude in X-ray luminosity ($\sim$10${}^{43}$ - 10${}^{45}$ erg s${}^{-1}$). AGN hosts are carefully mass and redshift matched to 486 control galaxies. A novel technique for identifying and quantifying merger features in galaxies is developed, subtracting GALFIT galaxy models and quantifying the residuals. Comparison to visual classification confirms this measure reliably picks out disturbance features in galaxies. No enhancement of merger features with increasing AGN luminosity is found with this metric, or by visual inspection. We analyse the redshift evolution of AGN associated with galaxy mergers and find no merger enhancement in lower redshift bins. Contrarily, in the highest redshift bin (z$\sim$2) AGN are $\sim$4 times more likely to be in galaxies exhibiting evidence of morphological disturbance compared to control galaxies, at 99% confidence level ($\sim$2.4$\sigma$) from visual inspection. Since only $\sim$15% of these AGN are found to be in morphologically disturbed galaxies, it is implied that major mergers at high redshift make a noticeable but subdominant contribution to AGN fuelling. At low redshifts other processes dominate and mergers become a less significant triggering mechanism.

17 pages, 15 figures

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• The radio loudness of SDSS quasars from the LOFAR Two-metre Sky Survey: ubiquitous jet activity and constraints on star formation
• Interacting galaxies in the IllustrisTNG simulations -- IV: Enhanced Supermassive Black Hole Accretion Rates in Post-Merger Galaxies
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• Hydrodynamical Simulations of the Triggering of Nuclear Activities by Minor Mergers of Galaxies
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• Using Machine Learning to Determine Morphologies of $z<1$ AGN Host Galaxies in the Hyper Suprime-Cam Wide Survey
• Merging history of massive galaxies at 3<z<6
• An ALMA Band 7 survey of SDSS/Herschel quasars in Stripe 82: I. The properties of the 870 micron counterparts
• Interactions among intermediate redshift galaxies. The case of SDSSJ134420.86+663717.8
• The major merger-active galactic nucleus connection up to the cosmic noon
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