The discovery of a massive supercluster at z = 0.9 in the UKIDSS DXS

We analyse the first publicly released deep field of the UKIDSS Deep eXtragalactic Survey (DXS) to identify candidate galaxy over-densities at z � 1 across �1 sq. degree in the ELAIS-N1 field. Using I K,J K and K 3.6µm colours we identify and spectroscopically follow-up five candidate structures with Gemini/GMOS and confirm they are all true over-densities with between five and nineteen members each. Surprisingly, all five structures lie in a narrow redshift range at z = 0.89 ± 0.01, although they are spread across 30Mpc on the sky. We also find a more distant overdensity at z = 1.09 in one of the spectroscopic survey regions. These five over-dense regions lying in a narrow redshift range indicate the presence of a supercluster in this field and by comparing with mock cluster catalogs from N-body simulations we discuss the likely properties of this structure. Overall, we show that the properties of this supercluster are similar to the well-studied Shapley and Hercules superclusters at lower redshift.