Study of dynamical and emission properties of dual/binary AGN candidate

Abstract

Galaxy mergers, apart from influencing the morphology of the merging galaxies as a whole, are also responsible for triggering accretion around the central supermassive black holes and influencing the dynamics around central black holes. When galaxies merge, the supermassive black hole which is present at the centre of each galaxy sink to the centre of the merged system. This forms an SMBH pair and may lead to a precessing jet. However, there are other mechanisms (e.g., presence of a tilted accretion disk) that may explain the precession of radio jets as well. This precessing jet model is often invoked to explain the inversion symmetry observed in S- and Z-shaped radio sources. The study of these sources and constraining the involved parameters may give us some important insights into the dynamics involved in the region near the black holes and the process of merging. Here, in our study, we have simulated these precessing jets using PLUTO code by integrat ing a system of magneto-hydrodynamical fluid equations in three-dimensional Cartesian coordinates, using a structured mesh approach to provide the time evolution of the dy namics of these galaxies. We used a simple kinematic model for a precessing jet with an initially toroidal magnetic field in the presence of an ambient medium and simulated it to study the formation and evolution of S-shaped galaxies in three-dimensional space. We have also produced multi-wavelength synthetic emission and spectral index maps by modelling non-thermal emission in these galaxies. We made use of the parameters in ferred from the observations of 2MASX J12032061+1319316, a candidate dual AGN to compare the results of the simulations to the observations. We explored the parameter space to produce the best match of simulated results with the observations. In our simulations, we saw that the density, pressure, and kinetic energy density distri bution in the jet has a helical nature. The synthetic emission maps featured an S-shaped morphology along with two hotspots, similar to the observations, which confirms that precessing jets can produce such morphology. The distance between two hotspots in our simulations came out to be lower than that in the observed images. This can be explained to be the e↵ect of the ambient medium, which is not assumed in the simple, kinematic model we have used to model jet precession. We found that the magnetic field has an ef fect on the dynamics of the jet, and it slows the jet down. It is also crucial in the emission mechanism of these galaxies. We found that these galaxies prefer equipartition between the thermal and magnetic pressure. Further, with the help of various Stokes parameters, we plotted the fractional polarization and the structure of the magnetic field near the jet. We found that these sources have a highly ordered magnetic field with maximum fractional polarization ⇠ 78%. Despite the initially toroidal nature of the magnetic field, the magnetic field lines follow the jet locus at later times. We have also investigated the ‘spectral age problem’ by studying the evolution of the equipartition condition between the energy in the magnetic fields and in radiation from non-thermal particles. We found that the equipartition condition is dynamic, which can explain the mismatch in calculated dynamical and spectral ages. Lastly, from di↵erent simulation setups explored in the study, we found the setup which matches best with the observation of this particular source. Key words: 2MASX J12032061+1319316, galaxy merger, precessing jets, dual AGNs, binary AGNs.