Title: GMOS Spectroscopy of z>1 Galaxy Clusters from the SpARCS Survey
Authors: Yee, H.K.C., Muzzin, A., & Wilson, G.

Abstract:

  The Spitzer Adaptation of the Red-sequence Cluster Survey combines deep 
z'-band ground-based and 3.6um Spitzer SWIRE images to find z>1 galaxy 
clusters using the cluster red-sequence method.  The 41.9 deg^2 area of 
the survey makes it the largest z>1 cluster survey.  We are conducting a 
large multiobject spectroscopy program using the node-&-shuffle mode on 
GMOS as part of a large multi-wavelength campaign to study in detail a 
sample of 10 rich clusters at 1<z<1.5.  We use the band-shuffle mode which 
populates the middle third of the GMOS field with microslits and shuffles 
the charges to the top and bottom third of the chips.  Because of the high 
density of galaxies over a small angular region in cores of high-redshift 
clusters, the band-shuffle mode makes Gemini plus GMOS arguable the most 
efficient combination for obtaining member redshifts in high-redshift clusters.  
We present spectroscopy of the first three rich SpARCS clusters observed in 
our program.  We obtained 17 and 28 confirmed members in two clusters at z~1.2 
using 3 and 4 masks on GMOS-N of 3hr integration each, and 9 members of a 
z=1.335 cluster using a single mask of 10hr exposure on GMOS-S.  We derived 
velocity dispersions of 650 to 1050 km/s, corresponding to cluster masses of 
1-9x10^14 M_sun, showing the efficiency of our program of finding and confirming 
massive clusters at z>1.  We also present preliminary results on galaxy 
population properties based on the spectroscopic and photometry data.
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