TY - JOUR
T1 - The XMM Cluster Survey
T2 - Galaxy morphologies and the color-magnitude relation in J2215.9 – 1738 AT z = 1.46
AU - Hilton, Matt
AU - Stanford, S. Adam
AU - Stott, John P.
AU - Collins, Chris A.
AU - Hoyle, Ben
AU - Davidson, Michael
AU - Hosmer, Mark
AU - Kay, Scott T.
AU - Liddle, Andrew R.
AU - Lloyd-davies, Ed
AU - Mann, Robert G.
AU - Mehrtens, Nicola
AU - Miller, Christopher J.
AU - Nichol, Robert C.
AU - Romer, A. Kathy
AU - Sabirli, Kivanc
AU - Sahlen, Martin
AU - Viana, Pedro T. P.
AU - West, Michael J.
AU - Barbary, Kyle
AU - Dawson, Kyle S.
AU - Meyers, Joshua
AU - Perlmutter, Saul
AU - Rubin, David
AU - Suzuki, Nao
PY - 2009/5/20
Y1 - 2009/5/20
N2 - 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 ~ 1. Within the central 0.5 Mpc, approximately ~62% of the galaxies identified as likely cluster members are ellipticals or S0s; and ~38% are spirals or irregulars. Therefore, early-type galaxies were already entrenched as the dominant galaxy population in at least some clusters approximately ~4.5 Gyr after the big bang. We measure the CMRs for the early-type galaxies, finding that the slope in the z 850-J relation is consistent with that measured in the Coma cluster, some ~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 ≈3 Gyr, corresponding to the major epoch of star formation coming to an end at zf ≈ 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 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.
AB - 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 ~ 1. Within the central 0.5 Mpc, approximately ~62% of the galaxies identified as likely cluster members are ellipticals or S0s; and ~38% are spirals or irregulars. Therefore, early-type galaxies were already entrenched as the dominant galaxy population in at least some clusters approximately ~4.5 Gyr after the big bang. We measure the CMRs for the early-type galaxies, finding that the slope in the z 850-J relation is consistent with that measured in the Coma cluster, some ~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 ≈3 Gyr, corresponding to the major epoch of star formation coming to an end at zf ≈ 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 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.
U2 - 10.1088/0004-637X/697/1/436
DO - 10.1088/0004-637X/697/1/436
M3 - Article
SN - 0004-637X
VL - 697
SP - 436
EP - 451
JO - The Astrophysical Journal
JF - The Astrophysical Journal
IS - 1
ER -