2001/04/16 by P. G. van Dokkum, S. A. Stanford, B. P. Holden +3 · 11 citations
Physics and Astronomy · #Astronomy and Astrophysical Research #Galaxies: Formation, Evolution, Phenomena #Stellar, planetary, and galactic studies #astro-ph
paper · pdf · doi:10.1086/320335
Accepted for publication in The Astrophysical Journal Letters
arxiv created 2001/04/16 · openalex publication_date 2001/05/10 · arxiv updated 2009/12/01 · openalex created_date 2019/06/27 · openalex updated_date 2026/07/31
We present a study of the galaxy population in the IR-selected cluster RX J0848+4453 at z = 1.27, using deep Hubble Space Telescope ( HST ) NICMOS H F160W and WFPC2 I F814W images of the cluster core. We morphologically classify all galaxies to K s = 20.6 that are covered by the HST imaging and determine photometric redshifts using deep ground-based BRIzJK s photometry. Of 22 likely cluster members with morphological classifications, 11 (50%) are classified as early-type galaxies, nine (41%) as spiral galaxies, and two (9%) as "merger/peculiar." At HST resolution, the second brightest cluster galaxy is resolved into a spectacular merger between three red galaxies of similar luminosity, separated from each other by ≈6 h kpc, with an integrated magnitude K = 17.6 (~3 L * at z = 1.27). The two most luminous early-type galaxies also show evidence for recent or ongoing interactions. Mergers and interactions between galaxies are possible because RX J0848+4453 is not yet relaxed. The fraction of early-type galaxies in our sample is similar to that in clusters at 0.5 < z < 1 and consistent with a gradual decrease of the number of early-type galaxies in clusters from z = 0 to z ≈ 1.3. We find evidence that the color-magnitude relation of the early-type galaxies is less steep than in the nearby Coma Cluster. This may indicate that the brightest early-type galaxies have young stellar populations at z = 1.27 but is also consistent with predictions of single-age "monolithic" models with a galactic wind. The scatter in the color-magnitude relation is ≈0.04 in rest-frame U - V , similar to that in clusters at 0 < z < 1. Taken together, these results show that luminous early-type galaxies exist in clusters at z ≈ 1.3 but that their number density may be smaller than in the local universe. Additional observations are needed to determine whether the brightest early-type galaxies harbor young stellar populations.