We present a candidate for the most distant galaxy known to date with a photometric redshift of z = 10.7$^{+0.6}$ $_{-0.4}$ (95% confidence limits; with z {lt} 9.5 galaxies of known types ruled... Show moreWe present a candidate for the most distant galaxy known to date with a photometric redshift of z = 10.7$^{+0.6}$ $_{-0.4}$ (95% confidence limits; with z {lt} 9.5 galaxies of known types ruled out at 7.2{$σ$}). This J-dropout Lyman break galaxy, named MACS0647-JD, was discovered as part of the Cluster Lensing and Supernova survey with Hubble (CLASH). We observe three magnified images of this galaxy due to strong gravitational lensing by the galaxy cluster MACSJ0647.7+7015 at z = 0.591. The images are magnified by factors of ~{}80, 7, and 2, with the brighter two observed at ~{}26th magnitude AB (~{}0.15 {$μ$}Jy) in the WFC3/IR F160W filter (~{}1.4-1.7 {$μ$}m) where they are detected at gsim12{$σ$}. All three images are also confidently detected at gsim6{$σ$} in F140W (~{}1.2-1.6 {$μ$}m), dropping out of detection from 15 lower wavelength Hubble Space Telescope filters (~{}0.2-1.4 {$μ$}m), and lacking bright detections in Spitzer/IRAC 3.6 {$μ$}m and 4.5 {$μ$}m imaging (~{}3.2-5.0 {$μ$}m). We rule out a broad range of possible lower redshift interlopers, including some previously published as high-redshift candidates. Our high-redshift conclusion is more conservative than if we had neglected a Bayesian photometric redshift prior. Given CLASH observations of 17 high-mass clusters to date, our discoveries of MACS0647-JD at z ~{} 10.8 and MACS1149-JD at z ~{} 9.6 are consistent with a lensed luminosity function extrapolated from lower redshifts. This would suggest that low-luminosity galaxies could have reionized the universe. However, given the significant uncertainties based on only two galaxies, we cannot yet rule out the sharp drop-off in number counts at z {gt}~{} 10 suggested by field searches. Show less
Lemze, D.; Postman, M.; Genel, S.; Ford, H.; Balestra, I.; Donahue, M.; ... ; Seitz, S. 2013
We provide a new observational test for a key prediction of the ΛCDM cosmological model: the contributions of mergers with different halo-to-main-cluster mass ratios to cluster-sized halo growth.... Show moreWe provide a new observational test for a key prediction of the ΛCDM cosmological model: the contributions of mergers with different halo-to-main-cluster mass ratios to cluster-sized halo growth. We perform this test by dynamically analyzing 7 galaxy clusters, spanning the redshift range 0.13 < z c < 0.45 and caustic mass range 0.4-1.5 $10^{15}, h_{0.73}^{-1}$ M ☉, with an average of 293 spectroscopically confirmed bound galaxies to each cluster. The large radial coverage (a few virial radii), which covers the whole infall region, with a high number of spectroscopically identified galaxies enables this new study. For each cluster, we identify bound galaxies. Out of these galaxies, we identify infalling and accreted halos and estimate their masses and their dynamical states. Using the estimated masses, we derive the contribution of different mass ratios to cluster-sized halo growth. For mass ratios between ~0.2 and ~0.7, we find a ~1σ agreement with ΛCDM expectations based on the Millennium simulations I and II. At low mass ratios, lesssim 0.2, our derived contribution is underestimated since the detection efficiency decreases at low masses, ~2 × 1014 $h_{0.73}^{-1}$ M ☉. At large mass ratios, gsim 0.7, we do not detect halos probably because our sample, which was chosen to be quite X-ray relaxed, is biased against large mass ratios. Therefore, at large mass ratios, the derived contribution is also underestimated. Show less
Medezinski, E.; Umetsu, K.; Nonino, M.; Merten, J.; Zitrin, A.; Broadhurst, T.; ... ; Zheng, W. 2013
The galaxy cluster MACS J0717.5+3745 (z = 0.55) is the largest known cosmic lens, with complex internal structures seen in deep X-ray, Sunyaev-Zel'dovich effect, and dynamical observations. We... Show moreThe galaxy cluster MACS J0717.5+3745 (z = 0.55) is the largest known cosmic lens, with complex internal structures seen in deep X-ray, Sunyaev-Zel'dovich effect, and dynamical observations. We perform a combined weak- and strong-lensing analysis with wide-field BVR $_c$ i'z' Subaru/Suprime-Cam observations and 16-band Hubble Space Telescope observations taken as part of the Cluster Lensing And Supernova survey with Hubble. We find consistent weak distortion and magnification measurements of background galaxies and combine these signals to construct an optimally estimated radial mass profile of the cluster and its surrounding large-scale structure out to 5 Mpc h $^{–1}$. We find consistency between strong-lensing and weak-lensing in the region where these independent data overlap, {lt}500 kpc h $^{–1}$. The two-dimensional weak-lensing map reveals a clear filamentary structure traced by distinct mass halos. We model the lensing shear field with nine halos, including the main cluster, corresponding to mass peaks detected above 2.5{$σ$}$_{κ}$. The total mass of the cluster as determined by the different methods is M $_{vir}$ {ap} (2.8 {plusmn} 0.4) { imes} 10$^{15}$ M $_{☉}$. Although this is the most massive cluster known at z {gt} 0.5, in terms of extreme value statistics, we conclude that the mass of MACS J0717.5+3745 by itself is not in serious tension with {$Lambda$}CDM, representing only a ~{}2{$σ$} departure above the maximum simulated halo mass at this redshift. Based in part on data collected at the Subaru Telescope, which is operated by the National Astronomical Society of Japan. Show less
