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
In this work, we analyze the mass distribution of MACSJ1206.2-0847, particularly focusing on the halo properties of its cluster members. The cluster appears relaxed in its X-ray emission, but has... Show moreIn this work, we analyze the mass distribution of MACSJ1206.2-0847, particularly focusing on the halo properties of its cluster members. The cluster appears relaxed in its X-ray emission, but has a significant amount of intracluster light that is not centrally concentrated, suggesting that galaxy-scale interactions are still ongoing despite the overall relaxed state. The cluster lenses 12 background galaxies into multiple images and one galaxy at z = 1.033 into a giant arc and its counterimage. The multiple image positions and the surface brightness (SFB) distribution of the arc, which is bent around several cluster members, are sensitive to the cluster galaxy halo properties. We model the cluster mass distribution with a Navarro-Frenk-White profile and the galaxy halos with two parameters for the mass normalization and the extent of a reference halo assuming scalings with their observed near-infrared light. We match the multiple image positions at an rms level of 0.''85 and can reconstruct the SFB distribution of the arc in several filters to a remarkable accuracy based on this cluster model. The length scale where the enclosed galaxy halo mass is best constrained is about 5 effective radii{mdash}a scale in between those accessible to dynamical and field strong-lensing mass estimates on the one hand and galaxy-galaxy weak-lensing results on the other hand. The velocity dispersion and halo size of a galaxy with m $_{160W, AB}$ = 19.2 and M $_{B, Vega}$ = -20.7 are {$σ$} = 150 km s$^{-1}$ and r {ap} 26 {plusmn} 6 kpc, respectively, indicating that the halos of the cluster galaxies are tidally stripped. We also reconstruct the unlensed source, which is smaller by a factor of ~{}5.8 in area, demonstrating the increase in morphological information due to lensing. We conclude that this galaxy likely has star-forming spiral arms with a red (older) central component. Show less
Balestra, I.; Vanzella, E.; Rosati, P.; Monna, A.; Grillo, C.; Nonino, M.; ... ; Umetsu, K. 2013
We present VIsible Multi-Object Spectrograph (VIMOS) observations of a galaxy quintuply imaged by the Frontier Fields galaxy cluster RXC J2248.7-4431 . This sub-, high- galaxy has been recently... Show moreWe present VIsible Multi-Object Spectrograph (VIMOS) observations of a galaxy quintuply imaged by the Frontier Fields galaxy cluster RXC J2248.7-4431 . This sub-, high- galaxy has been recently discovered by Monna et al. (2013) using dropout techniques with the 16-band HST photometry acquired as part of the Cluster Lensing And Supernova survey with Hubble (CLASH). Obtained as part of the CLASH-VLT survey, the VIMOS medium-resolution spectra of this source show a very faint continuum between 8700 å and 9300 å and a prominent emission line at 8643 , which can be readily identified with Lyman- at . The emission line exhibits an asymmetric profile, with a more pronounced red wing. The rest-frame equivalent width of the line is , relatively well constrained thanks to the detection of the UV continuum, which is rarely achieved for a sub- galaxy at this redshift. After correcting formagnification, the star formation rate (SFR) estimated from the Ly line is SFRLyyr and that estimated from the UV data is SFRUVyr. We estimate that the effective radius of the source is kpc, which implies a star formation surface mass density yrkpc and, using the Kennicutt-Schmidt relation, a gas surface mass density pc. Our results support the idea that this magnified, distant galaxy is a young and compact object with luminosity at , when the Universe was just 1 Gyr old, with a similar amount of mass in gas and stars. In the spirit of the Frontier Fields initiative, we also publish the redshifts of several multiply imaged sources and other background objects, which will help improving the strong-lensing model of this galaxy cluster. This work is based on data collected at ESO VLT (prog.ID 186.A-0798) and at NASA HST. 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
