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How do the brightest AGN cluster at small scales ?

 Measurements of quasar clustering at small scales open up a  new arena for testing our galaxy formation. We compared predictions from MassiveBlack II against observations


Example of a binary quasar system in MassiveBlack II simulation. The white crosses show the positions of the two quasars living at the centers of  two distinct galaxies (blue and green histograms). Both the galaxies live within a parent dark matter halo (grey histogram) 

We find that our predictions of binary quasar clustering do not conflict with observations, marking a significant success of galaxy formation in explaining these extremely rare manifestations of non-linear structure. 


Quasar luminosity functions (left) and small scale quasar clustering (right) for the MassiveBlack II simulation vs observational measurements. We can construct a halo occupation distribution (conditional luminosity function / CLF) model that is able to self-consistently explain both simulations and observations.

Simulations indicate that these pairs likely correspond to extremely luminous quasars in satellite galaxies which are triggered by galaxy mergers. Multiple sequence of such galaxy mergers can also lead to formation quasar triples and quadruples. Several detections of such exotic systems have been made in the recent past. These systems are also formed in the Massive Black II simulation. 

triples and quadruples
triples and quadruples

For more details, please refer to Bhowmick et al 2019, Bhowmick et al 2020

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