Studies of black hole spin and other parameters as a function of redshift provide information about the physical state and merger and accretion histories of the systems .
One way that black hole spin may be estimated is through observations of extended radio sources .
These sources , powered by outflows from an AGN , allow the beam power and total outflow energy to be studied .
In a broad class of models , the beam power of the outflow is related to the spin of the black hole .
This relationship is used to estimate black hole spins for 55 radio sources .
The samples studied include 7 FRII quasars and 19 FRII radio galaxies with redshifts between 0.056 and 1.79 , and 29 radio sources associated with CD galaxies with redshifts between 0.0035 and 0.291 .
The FRII sources studied have estimated spin values of between about 0.2 and 1 ; there is a range of values at a given redshift , and the values tend to increase with increasing redshift .
Results obtained for FRII quasars are very similar to those obtained for FRII galaxies .
A broader range of spin values are obtained for the sample of radio sources associated with CD galaxies studied .
The fraction of the spin energy extracted per outflow event is estimated and ranges from about 0.03 to 0.5 for FRII sources and 0.002 to about 1 for radio sources associated with CD galaxies ; the data are consistent with this fraction being independent of redshift though the uncertainties are large .
The results obtained are consistent with those predicted by numerical simulations that track the merger and accretion history of AGN , supporting the idea that , for AGN with powerful large-scale outflows , beam power is directly related to black hole spin .