We present an in-depth analysis of the Butcher-Oemler cluster A2111 , including new optical spectroscopy plus a deep Very Large Array ( VLA ) radio continuum observation .
These are combined with optical imaging from the Sloan Digital Sky Survey ( SDSS ) to assess the activity and properties of member galaxies .
Prior X-ray studies have suggested A2111 is a head-on cluster merger , a dynamical state which might be connected to the high level of activity inferred from its blue fraction .
We are able to directly assess this claim , using our spectroscopic data to identify 95 cluster members among 196 total galaxy spectra .
These galaxy velocities do not themselves provide significant evidence for the merger interpretation , however they are consistent with it provided the system is viewed near the time of core passage and at a viewing angle \gtrsim 30° different from the merger axis .
The SDSS data allow us to confirm the high blue fraction for A2111 , f _ { b } = 0.15 \pm 0.03 based on photometry alone and f _ { b } = 0.23 \pm 0.03 using spectroscopic data to remove background galaxies .
We are able to detect 175 optical sources from the SDSS in our VLA radio data , of which 35 have redshift information .
We use the SDSS photometry to determine photometric redshifts for the remaining 140 radio-optical sources .
In total we identify up to 26 cluster radio galaxies , 14 of which have spectroscopic redshifts .
The optical spectroscopy and radio data reveal a substantial population of dusty starbursts within the cluster .
The high blue fraction and prevalence of star formation is consistent with the hypothesis that dynamically-active clusters are associated with more active member galaxies than relaxed clusters .