Central supermassive black holes ( SMBHs ) are a ubiquitous feature of locally-observed galaxies , and ample evidence suggests that the growth of SMBHs and their host galaxies is closely linked .
However , in the event of a merger , gravitational-wave ( GW ) recoil may displace a SMBH from its galactic center , or eject it entirely .
To explore the consequences of this phenomenon , we use hydrodynamic simulations of gaseous galaxy mergers that include a range of BH recoil velocities .
We have generated a suite of over 200 simulations with more than 60 merger models , enabling us to identify systematic trends in the behavior of recoiling BHs – specifically ( i ) their dynamics , ( ii ) their observable signatures , and ( iii ) their effects on BH/galaxy co-evolution .
( i ) Recoiling BH trajectories depend heavily on the gas content of the host galaxy ; maximal BH displacements from the center may vary by up to an order of magnitude between gas-rich and gas-poor mergers .
In some cases , recoil trajectories also depend on the timing of the BH merger relative to the formation of the galaxy merger remnant .
( ii ) Recoiling BHs may be observable as offset active galactic nuclei ( AGN ) via either kinematic offsets ( v > 800 km s ^ { -1 } ) or spatial offsets ( R > 1 kpc ) for lifetimes of about 1 - 100 Myr .
In addition , recoil events affect the total AGN lifetime .
GW recoil generally reduces the lifetimes of bright AGN , but may extend lower-luminosity AGN lifetimes .
( iii ) Rapidly-recoiling BHs may be up to about 5 times less massive than their stationary counterparts .
These mass deficits lower the normalization of the M - \sigma relation and contribute to both intrinsic and overall scatter .
Furthermore , recoil events displace AGN feedback from the galactic center , which enhances central star formation rates .
This results in longer starburst phases and higher central stellar densities in merger remnants .