Coalescence of intermediate-mass black holes ( IMBHs ) as a result of the migration toward galactic centers via dynamical friction may contribute to the formation of supermassive BHs .
Here we reinvestigate the gaseous dynamical friction , which was claimed to be inefficient with radiative feedback from BHs in literature , by performing 3D radiation-hydrodynamics simulations that solve the flow structure in the vicinity of BHs .
We consider a 10 ^ { 4 } ~ { } \mathrm { M } _ { \odot } BH moving at the velocity v _ { \mathrm { flow } } through the homogeneous medium with metallicity Z in the range of 0 - 0.1 ~ { } \mathrm { Z } _ { \odot } and density n _ { \infty } .
We show that , if n _ { \infty } \lesssim 10 ^ { 6 } ~ { } \mathrm { cm ^ { -3 } } and v _ { \mathrm { flow } } \lesssim 60 ~ { } \mathrm { km~ { } s ^ { -1 } } , the BH is accelerated forward because of the gravitational pull from a dense shell ahead of an ionized bubble around the BH , regardless of the value of Z .
If n _ { \infty } \gtrsim 10 ^ { 6 } ~ { } \mathrm { cm ^ { -3 } } , however , our simulation shows the opposite result .
The ionized bubble and associating shell temporarily appear , but immediately go downstream with significant ram pressure of the flow .
They eventually converge into a massive downstream wake , which gravitationally drags the BH backward .
The BH decelerates over the timescale of \sim 0.01 Myr , much shorter than the dynamical timescale in galactic disks .
Our results suggest that IMBHs that encounter the dense clouds rapidly migrate toward galactic centers , where they possibly coalescence with others .