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arXiv · 1908.01732

A Triple AGN in a Mid-Infrared Selected Late Stage Galaxy Merger

Ryan W. Pfeifle·Shobita Satyapal·Christina Manzano-King·Jenna Cann·Remington O. Sexton·Barry Rothberg·Gabriela Canalizo·Claudio Ricci·Laura Blecha·Sara L. Ellison·Mario Gliozzi·Nathan J. Secrest·Anca Constantin·Jenna B. Harvey
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Abstract

The co-evolution of galaxies and the supermassive black holes (SMBHs) at their centers via hierarchical galaxy mergers is a key prediction of $\Lambda$CDM cosmology. As gas and dust are funneled to the SMBHs during the merger, the SMBHs light up as active galactic nuclei (AGNs). In some cases, a merger of two galaxies can encounter a third galaxy, leading to a triple merger, which would manifest as a triple AGN if all three SMBHs are simultaneously accreting. Using high-spatial resolution X-ray, near-IR, and optical spectroscopic diagnostics, we report here a compelling case of an AGN triplet with mutual separations < 10 kpc in the advanced merger SDSS J084905.51+111447.2 at z = 0.077. The system exhibits three nuclear X-ray sources, optical spectroscopic line ratios consistent with AGN in each nucleus, a high excitation near-IR coronal line in one nucleus, and broad Pa$\alpha$ detections in two nuclei. Hard X-ray spectral fitting reveals a high column density along the line of sight, consistent with the picture of late-stage mergers hosting heavily absorbed AGNs. Our multiwavelength diagnostics support a triple AGN scenario, and we rule out alternative explanations such as star formation activity, shock-driven emission, and emission from fewer than three AGN. The dynamics of gravitationally bound triple SMBH systems can dramatically reduce binary SMBH inspiral timescales, providing a possible means to surmount the "Final Parsec Problem." AGN triplets in advanced mergers are the only observational forerunner to bound triple SMBH systems and thus offer a glimpse of the accretion activity and environments of the AGNs prior to the gravitationally-bound triple phase.

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Ryan W. Pfeifle, Shobita Satyapal, Christina Manzano-King, Jenna Cann, Remington O. Sexton, Barry Rothberg, Gabriela Canalizo, Claudio Ricci, Laura Blecha, Sara L. Ellison, Mario Gliozzi, Nathan J. Secrest, Anca Constantin, Jenna B. Harvey. 2019-08-05. A Triple AGN in a Mid-Infrared Selected Late Stage Galaxy Merger. https://doi.org/10.3847/1538-4357/ab3a9b

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