Tom Broadhurst

CLASH: three strongly lensed images of a candidate z ≈ 11 galaxy

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.

A magnified young galaxy from about 500 million years after the Big Bang

Re-ionization of the intergalactic medium occurred in the early Universe at redshift z ≈ 6–11, following the formation of the first generation of stars. Those young galaxies (where the bulk of stars formed) at a cosmic age of less than about 500 million years (z ≲ 10) remain largely unexplored because they are at or beyond the sensitivity limits of existing large telescopes. Understanding the properties of these galaxies is critical to identifying the source of the radiation that re-ionized the intergalactic medium. Gravitational lensing by galaxy clusters allows the detection of high-redshift galaxies fainter than what otherwise could be found in the deepest images of the sky. Here we report multiband observations of the cluster MACS J1149+2223 that have revealed (with high probability) a gravitationally magnified galaxy from the early Universe, at a redshift of z = 9.6 ± 0.2 (that is, a cosmic age of 490 ± 15 million years, or 3.6 per cent of the age of the Universe). We estimate that it formed less than 200 million years after the Big Bang (at the 95 per cent confidence level), implying a formation redshift of ≲14. Given the small sky area that our observations cover, faint galaxies seem to be abundant at such a young cosmic age, suggesting that they may be the dominant source for the early re-ionization of the intergalactic medium.Johns Hopkins University, 3701 San Martin Drive, Baltimore , MD 21218, U.S.A. Space Telescope Science Institute Universität Heidelberg University of California, San Diego University of Science and Technology of China University College London Institute de Ciencies de l’Espai Instituto de Astrofı́sica de Andalucı́a Jet Propulsion Laboratory, California Institute of Techno logy Pontificia Universidad Católica de Chile National Optical Astronomical Observatory Universitas Sternwarte, München Leiden Observatory University of Basque Country

Mapping cluster mass distributions via gravitational lensing of background galaxies

We present a new method for measuring the projected mass distributions of galaxy clusters. The gravitational amplification is measured by comparing the joint distribution in redshift and magnitude of galaxies behind the cluster with that of field galaxies. We show that the total amplification is directly related to the surface mass density in the weak field limit, and so it is possible to map the mass distribution of the cluster. The method is shown to be limited by discreteness noise and galaxy clustering behind the lens. Galaxy clustering sets a lower limit to the error along the redshift direction, but a clustering independent lensing signature may be obtained from the magnitude distribution at fixed redshift. Statistical techniques are developed for estimating the surface mass density of the cluster. We extend these methods to account for any obscuration by cluster halo dust, which may be mapped independently of the dark matter. We apply the method to a series of numerical simulations and show the feasibility of the approach. We consider approximate redshift information, and show how the mass estimates are degraded.

Creation of cosmic structure in the complex galaxy cluster merger Abell 2744

We present a detailed strong lensing, weak lensing and X-ray analysis of Abell 2744 (z = 0:308), one of the most actively merging galaxy clusters known. It appears to have unleashed ‘dark’, ‘ghost’, ‘bullet’ and ‘stripped’ substructures, each 10 14 M . The phenomenology is complex and will present a challenge for numerical simulations to reproduce. With new, multiband HST imaging, we identify 34 strongly-lensed images of 11 galaxies around the massive Southern ‘core’. Combining this with weak lensing data from HST, VLT and Subaru, we produce the most detailed mass map of this cluster to date. We also perform an independent analysis of archival Chandra X-ray imaging. Our analyses support a recent claim that the Southern core and Northwestern substructure are post-merger and exhibit morphology similar to the Bullet Cluster viewed from an angle. From the separation between X-ray emitting gas and lensing mass in the Southern core, we derive a new and independent constraint on the self-interaction cross section of dark matter particles =m

A census of star-forming galaxies in the z ∼ 9-10 universe based on hst+spitzer observations over 19 clash clusters: Three candidate z ∼ 9-10 galaxies and improved constraints on the star formation rate density at z

We utilise a two-color Lyman-Break selection criterion to search for z � 9-10 galaxies over the first 19 clusters in the CLASH program. Key to this search are deep observations over our clusters in five near-IR passbands to 1.6µm, allowing us good constraints on the position of the Lyman break to z � 10. A systematic search yields three z � 9-10 candidates in total above a 6� detection limit. While we have already reported the most robust of these candidates, MACS1149-JD, in a previous publication, two additional z � 9 candidates are also revealed in our expanded search. The new candidates have H160-band AB magnitudes of �26.2-26.9 and are located behind MACSJ1115.9+0129 and MACSJ1720.3+3536. The observed H160 Spitzer/IRAC colors for the sources are sufficiently blue to strongly favor redshifts of z � 9 for these sources. A careful assessment of various sources of contamination suggests .1 contaminants for our z � 9-10 selection. To determine the implications of these search results for the LF and SFR density at z � 9, we introduce a new differential approach to deriving these quantities in lensing fields. Our procedure is to derive the evolution by comparing the number of z � 9-10 galaxy candidates found in CLASH with the number of galaxies in a slightly lower redshift sample (after correcting for the differences in selection volumes), here taken to be z � 8. This procedure takes advantage of the fact that the relative selection volumes available for the z � 8 and z � 9-10 selections behind lensing clusters are not greatly dependent on the details of the gravitational lensing models. We find that the normalization of the UV LF at z � 9 is just 0.22 +0.30 −0.15 × that at z � 8, �2 +31× lower than what we would infer extrapolating z � 4-8 LF results. These results therefore suggest a more rapid evolution in the UV LF at z > 8 than seen at lower redshifts (although the current evidence here is weak). Compared to similar evolutionary findings from the HUDF, our result is much more insensitive to large-scale structure uncertainties, given our many independent sightlines on the high-redshift universe. Subject headings: galaxies: evolution — galaxies: high-redshift

CLASH: Weak-lensing Shear-and-magnification Analysis of 20 Galaxy Clusters

We present a joint shear-and-magnification weak-lensing analysis of a sample of 16 X-ray-regular and 4 high-magnification galaxy clusters at 0.19 ≾ z ≾ 0.69 selected from the Cluster Lensing And Supernova survey with Hubble (CLASH). Our analysis uses wide-field multi-color imaging, taken primarily with Suprime-Cam on the Subaru Telescope. From a stacked-shear-only analysis of the X-ray-selected subsample, we detect the ensemble-averaged lensing signal with a total signal-to-noise ratio of ≃ 25 in the radial range of 200-3500 kpc h^(–1), providing integrated constraints on the halo profile shape and concentration-mass relation. The stacked tangential-shear signal is well described by a family of standard density profiles predicted for dark-matter-dominated halos in gravitational equilibrium, namely, the Navarro-Frenk-White (NFW), truncated variants of NFW, and Einasto models. For the NFW model, we measure a mean concentration of c_(200c)=4.01^(+0.35)_(-0.32) at an effective halo mass of M_(200c)=1.34^(+0.10)_(-0.09) x 10^(15)M_☉. We show that this is in excellent agreement with Λ cold dark matter (ΛCDM) predictions when the CLASH X-ray selection function and projection effects are taken into account. The best-fit Einasto shape parameter is ɑ_E=0.191^(+0.071)_(-0.068), which is consistent with the NFW-equivalent Einasto parameter of ~0.18. We reconstruct projected mass density profiles of all CLASH clusters from a joint likelihood analysis of shear-and-magnification data and measure cluster masses at several characteristic radii assuming an NFW density profile. We also derive an ensemble-averaged total projected mass profile of the X-ray-selected subsample by stacking their individual mass profiles. The stacked total mass profile, constrained by the shear+magnification data, is shown to be consistent with our shear-based halo-model predictions, including the effects of surrounding large-scale structure as a two-halo term, establishing further consistency in the context of the ΛCDM model.

Advanced camera for the Hubble Space Telescope

The Advanced Camera for the Hubble Space Telescope has three cameras. The first, the Wide Field Camera, will be a high- throughput, wide field, 4096 X 4096 pixel CCD optical and I-band camera that is half-critically sampled at 500 nm. The second, the High Resolution Camera (HRC), is a 1024 X 1024 pixel CCD camera that is critically sampled at 500 nm. The HRC has a 26 inch X 29 inch field of view and 29 percent throughput at 250 nm. The HRC optical path includes a coronagraph that will improve the HST contrast near bright objects by a factor of approximately 10 at 900 nm. The third camera, the solar-blind camera, is a far-UV, pulse-counting array that has a relatively high throughput over a 26 inch X 29 inch field of view. The advanced camera for surveys will increase HSTs capability for surveys and discovery by a factor of approximately 10 at 800 nm.

Cosmic structure as the quantum interference of a coherent dark wave

A cosmological model treating dark matter as a coherent quantum wave agrees well with conventional dark-matter theory on an astronomical scale. But on smaller scales, the quantum nature of wave-like dark matter can explain dark-matter cores that are observed in dwarf galaxies, which standard theory cannot.

Strong-lensing analysis of a complete sample of 12 MACS clusters at z > 0.5: mass models and Einstein radii

We present the results of a strong-lensing analysis of a complete sample of 12 very luminous X-ray clusters at z > 0:5 using HST/ACS images. Our modelling technique has uncovered some of the largest known critical curves outlined by many accuratelypredicted sets of multiple images. The distribution of Einstein radii has a median value of’ 28 00 (for a source redshift of zs 2), twice as large as other lower-z samples, and extends to 55 00 for MACS J0717.5+3745, with an impressive enclosed Einstein mass of 7:4 10 14 M . We

New Multiply-Lensed Galaxies Identified in ACS/NIC3 Observations of Cl0024+1654, Using an Improved Mass Model

We present an improved strong-lensing analysis of Cl0024+1654 (z = 0.39) using deep Hubble Space Telescope (HST)/Advanced Camera for Surveys (ACS)/NIC3 images, based on 33 multiply-lensed images of 11 background galaxies. These are found with a model that assumes mass approximately traces light, with a low-order expansion to allow for flexibility on large scales. The model is constrained initially by the well-known five-image system (z = 1.675) and refined as new multiply-lensed systems are identified using the model. Photometric redshifts of these new systems are then used to constrain better the mass profile by adopting the standard cosmological relation between redshift and lensing distance. Our model requires only six free parameters to describe well all positional and redshift data. The resulting inner mass profile has a slope of d log M/ dl ogr �− 0.55, consistent with new weak-lensing measurements where the data overlap, at r � 200 kpc/h70. The combined profile is well fitted by a high-concentration Navarro, Frenk & White (NFW) mass profile, Cvir ∼ 8.6 ± 1.6,