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Two candidates for dual AGN in dwarf-dwarf galaxy mergers

Presentation #106A.02 in the session Active Galactic Nuclei I.

Published onJul 01, 2023
Two candidates for dual AGN in dwarf-dwarf galaxy mergers

One approach to study the earliest stages of the evolution of black holes and galaxies is to detect local analogs. This can be accomplished by studying local dwarf-dwarf galaxy mergers since simulations and observations of the UV luminosity function suggest that dwarf galaxies are the most common type of galaxies at high redshifts. Therefore, local mergers of dwarf galaxies and their central black holes would accurately mimic the earliest stages of growth of cosmic structures. We report the discovery of two candidates for dual AGN in dwarf-dwarf mergers, the first examples of their kind. The first object is an Abell 133 (z=0.05) dwarf galaxy and it exhibits tidal debris in the form of a long, clumpy tidal tail and a smaller countertail. These tails were only revealed after we applied adaptive smoothing on optical images, they are not visible in any other large survey, and would have stayed undetected otherwise. The galaxy and the first clump of the tidal tail harbor luminous X-ray sources, and WISE detected an infrared counterpart to the X-ray source in the tail with AGN-consistent colors. We interpret the longer tail to be a remnant of an even smaller dwarf galaxy that got tidally disrupted by forces from its more massive neighbor, implying that we are observing a late-stage merger. The second object consists of two dwarf galaxies, likely members of the Abell 1758S cluster (z=0.27), connected by a tidal bridge. These galaxies are in the early stages of merging, and the more massive one is stripping material from its smaller companion. The tidal bridge was revealed upon applying adaptive smoothing on optical images and is invisible otherwise. Also, the smaller galaxy does not exist in any catalog and was first observed in our work thanks to the adaptive smoothing procedure. Both galaxies have luminous X-ray sources, and the smaller galaxy has a WISE-detected infrared counterpart with AGN-consistent colors. In this talk I will discuss the nature of these galaxies and present evidence for their dwarf nature, I will discuss alternative explanations for the nature of X-ray sources and argue that the AGN scenario is the most likely one, and I will discuss the adaptive smoothing technique that allowed detection of previously unknown galaxy mergers.

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