We studied the final phases of galactic mergers , focusing on interactions between supermassive black holes ( SMBHs ) and the interstellar medium in a central sub-kpc region , using an N-body/hydrodynamics code .
This numerical experiment aims to understand the fate of the gas supplied by mergers of two or more galaxies with SMBHs , whose masses are 10 ^ { 7 } M _ { \odot } .
We observed that the mass accretion rate to one SMBH exceeds the Eddington accretion rate when the distance between two black holes ( BHs ) rapidly decreases .
However , this rapid accretion phase does not last for more than 10 ^ { 7 } yrs , and it drops to \sim 10 % of the Eddington rate in the quasi-steady accretion phase .
The rapid accretion is caused by the angular momentum transfer from the gas to the stellar component , and the moderate accretion in the quasi-steady phase is caused by turbulent viscosity and gravitational torque in the disk .
The second merger event enhances the mass accretion to the BHs ; however , this phase takes place on a similar timescale to the first merger event .
We also found that the AGN feedback and the mass accretion to BHs can coexist in the central region of merged galaxies , if the amount of feedback energy is given as ( 2 \times 10 ^ { -4 } -2 \times 10 ^ { -3 } ) \dot { M } c ^ { 2 } , where \dot { M } is the accretion rate to r = 1 pc .
The accretion rate is suppressed by \sim 1/50 in the quasi-steady accretion phase for 0.02 \dot { M } c ^ { 2 } .
The fraction of the gas that finally falls to each BH is approximately 5–7 % of the supplied total gas mass ( 10 ^ { 8 } M _ { \odot } ) , and 15–20 % of the gas forms a circumnuclear gas inside 100 pc .
This remnant gas heavily obscures the luminous phase of the active galactic nuclei ( AGN ) during merger events , and the moderate AGN feedback does not alter this property .