Near-Infrared Imaging of a Group or Cluster of Galaxies at a Redshift of 2.39

Abstract

At z=2.39, the cluster around 53W002 is one of the most distant groups or clusters of galaxies known to date. At this redshift the 4000A-break falls between the J and H bands, thus our infrared observations are designed to identify cluster members by a red J-H colour. Out of the 42 objects we have detected in the field, we find ten galaxies with J-H>1.0 and K>18.8, redder and fainter than the radio galaxy, and consistent with the presence of a 4000A-break at the cluster redshift. Two of these reddest galaxies have been confirmed spectroscopically. The colours, sizes and location of these infrared-selected galaxies suggest a cluster much more similar to those nearby than revealed by Hubble Space Telescope observations alone.