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München, Germany

Coe D.,US Space Telescope Science Institute | Zitrin A.,Institute For Theoretische Astrophysik | Carrasco M.,Institute For Theoretische Astrophysik | Carrasco M.,University of Santiago de Chile | And 24 more authors.
Astrophysical Journal | Year: 2013

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 < 9.5 galaxies of known types ruled out at 7.2σ). 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 μJy) in the WFC3/IR F160W filter (∼1.4-1.7 μm) where they are detected at ≳12σ. All three images are also confidently detected at ≳6σ in F140W (∼1.2-1.6 μm), dropping out of detection from 15 lower wavelength Hubble Space Telescope filters (∼0.2-1.4 μm), and lacking bright detections in Spitzer/IRAC 3.6 μm and 4.5 μm imaging (∼3.2-5.0 μm). 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 ≳ 10 suggested by field searches. © 2013. The American Astronomical Society. All rights reserved.

Lemze D.,Johns Hopkins University | Postman M.,US Space Telescope Science Institute | Genel S.,Harvard - Smithsonian Center for Astrophysics | Ford H.C.,Johns Hopkins University | And 42 more authors.
Astrophysical Journal | Year: 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. 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 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, ≲ 0.2, our derived contribution is underestimated since the detection efficiency decreases at low masses, ∼2 × 1014 M ⊙. At large mass ratios, ≳ 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. © 2013. The American Astronomical Society. All rights reserved.

Zitrin A.,Tel Aviv University | Broadhurst T.,University of the Basque Country | Broadhurst T.,Ikerbasque | Coe D.,US Space Telescope Science Institute | And 40 more authors.
Astrophysical Journal | Year: 2011

We examine the inner mass distribution of the relaxed galaxy cluster A383 (z = 0.189), in deep 16band Hubble Space Telescope/ACS+WFC3 imaging taken as part of the Cluster Lensing And Supernova survey with Hubble (CLASH) multi-cycle treasury program. Our program is designed to study the dark matter distribution in 25 massive clusters, and balances depth with a wide wavelength coverage, 2000-16000 Å, to better identify lensed systems and generate precise photometric redshifts. This photometric information together with the predictive strength of our strong-lensing analysis method identifies 13 new multiply lensed images and candidates, so that a total of 27 multiple images of nine systems are used to tightly constrain the inner mass profile gradient, dlog Σ/dlog r ≃ -0.6 0.1 (r < 160kpc). We find consistency with the standard distance-redshift relation for the full range spanned by the lensed images, 1.01 < z < 6.03, with the higher-redshift sources deflected through larger angles as expected. The inner mass profile derived here is consistent with the results of our independent weak-lensing analysis of wide-field Subaru images, with good agreement in the region of overlap (0.7-1 arcmin). Combining weak and strong lensing, the overall mass profile is well fitted by a Navarro-Frenk-White profile with M vir = (5.37 +0.70 - 0.63± 0.26) × 1014 M ⊙ h -1 and a relatively high concentration, c vir = 8.77+0.44 - 0.42± 0.23, which lies above the standard c-M relation similar to other well-studied clusters. The critical radius of A383 is modest by the standards of other lensing clusters, rE ≃ 16 2″ (for zs = 2.55), so the relatively large number of lensed images uncovered here with precise photometric redshifts validates our imaging strategy for the CLASH survey. In total we aim to provide similarly high-quality lensing data for 25 clusters, 20 of which are X-ray-selected relaxed clusters, enabling a precise determination of the representative mass profile free from lensing bias. © 2011. The American Astronomical Society. All rights reserved.

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