THE XMM CLUSTER SURVEY: GALAXY MORPHOLOGIES AND THE COLOR-MAGNITUDE RELATION IN XMMXCS J2215.9 - 1738 AT z = 1.46
- Astrophysics and Cosmology Research Unit, School of Mathematical Sciences, University of KwaZulu-Natal, Private Bag X54001, Durban 4000 (South Africa)
- University of California, Davis, CA 95616 (United States)
- Astrophysics Research Institute, Liverpool John Moores University, Twelve Quays House, Egerton Wharf, Birkenhead CH41 1LD (United Kingdom)
- Institute of Cosmology and Gravitation, University of Portsmouth, Portsmouth PO1 2EG (United Kingdom)
- Institute of Astronomy, University of Edinburgh, Blackford Hill, Edinburgh EH9 9HJ (United Kingdom)
- Astronomy Centre, University of Sussex, Falmer, Brighton BN1 9QH (United Kingdom)
- University of Manchester, Jodrell Bank Observatory, Macclesfield, Cheshire SK11 9DL (United Kingdom)
- Cerro-Tololo Inter-American Observatory, National Optical Astronomy Observatory, 950 North Cherry Avenue, Tucson, AZ 85719 (United States)
- Departmento de Matematica Aplicada da Faculdade de Ciencias da Universidade do Porto, Rua do Campo Alegre 687, 4169-007 (Portugal)
- European Southern Observatory, Alonso de Cordova 3107, Vitacura, Casilla 19001, Santiago 19 (Chile)
- E. O. Lawrence Berkeley National Laboratory, 1 Cyclotron Road, Berkeley, CA 94720 (United States)
We present a study of the morphological fractions and color-magnitude relation (CMR) in the most distant X-ray selected galaxy cluster currently known, XMMXCS J2215.9 - 1738 at z = 1.46, using a combination of optical imaging data obtained with the Hubble Space Telescope Advanced Camera for Surveys, and infrared data from the Multi-Object Infrared Camera and Spectrograph, mounted on the 8.2 m Subaru telescope. We find that the morphological mix of the cluster galaxy population is similar to clusters at z {approx} 1. Within the central 0.5 Mpc, approximately {approx}62% of the galaxies identified as likely cluster members are ellipticals or S0s; and {approx}38% are spirals or irregulars. Therefore, early-type galaxies were already entrenched as the dominant galaxy population in at least some clusters approximately {approx}4.5 Gyr after the big bang. We measure the CMRs for the early-type galaxies, finding that the slope in the z {sub 850}-J relation is consistent with that measured in the Coma cluster, some {approx}9 Gyr earlier, although the uncertainty is large. In contrast, the measured intrinsic scatter about the CMR is more than three times the value measured in Coma, after conversion to rest-frame U - V. From comparison with stellar population synthesis models, the intrinsic scatter measurements imply mean luminosity-weighted ages for the early-type galaxies in J2215.9 - 1738 of {approx}3 Gyr, corresponding to the major epoch of star formation coming to an end at z{sub f} {approx} 3-5. We find that the cluster exhibits evidence of the 'downsizing' phenomenon: the fraction of faint cluster members on the red sequence expressed using the Dwarf-to-Giant Ratio (DGR) is 0.32 {+-} 0.18 within a radius of 0.5R {sub 200}. This is consistent with extrapolation of the redshift evolution of the DGR seen in cluster samples at z < 1. In contrast to observations of some other z > 1 clusters, we find a lack of very bright galaxies within the cluster.
- OSTI ID:
- 21300587
- Journal Information:
- Astrophysical Journal, Vol. 697, Issue 1; Other Information: DOI: 10.1088/0004-637X/697/1/436; Country of input: International Atomic Energy Agency (IAEA); ISSN 0004-637X
- Country of Publication:
- United States
- Language:
- English
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