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Do galaxy mergers drive AGN activity?

To explore the possible connection between galaxy mergers and AGN activity, we identified Black hole systems in Illustris-TNG and looked for enhancements in AGN activity within them.


A few examples of BH systems at various separations. The green circles mark the positions of BHs. The 2D color plots show the gas distributions in their surrounding environment. These represent host galaxies at different stages of mergers. Dark red to bright yellow represents low to high gas densities. The background panel in grayscale shows the large scale dark matter density field.

We find enhanced AGN activity at scales < 0.1, 0.01 Mpc, not at scales of ~1 Mpc. This is a strong signature of Merger-AGN connection. However, the majority of AGNs are not associated with mergers; they are likely driven by secular actovity.


AGN fractions of BH systems as a function of multiplicity. The solid lines show the AGN fractions of true BH systems. Dashed and dotted lines show AGN fractions of random sets of BHs. AGN fractions are enhanced for the true BH pairs and multiples within 0.1,0.01 Mpc/h.


The fraction of AGN which are associated with companion BHs within a BH system as a function of threshold Eddington ratio. The solid lines correspond to true BH systems. Dashed lines are random sets of BHs. The most luminous AGN have enhanced likelihood of having companions within 0.1,0.01 Mpc/h.

For more details, please refer to Bhowmick et al 2020

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