Strong Lensing Analysis of the Powerful Lensing Cluster MACS J2135.2-0102 (zz=0.33)

We present a light-traces-mass (LTM) strong-lensing model of the massive lensing cluster MACS J2135.2-0102 ($z$=0.33; hereafter MACS2135), known in part for hosting the Cosmic Eye galaxy lens. MACS2135 is also known to multiply-lens a $z=$2.3 sub-mm galaxy near the Brightest Cluster Galaxy (BCG), as well as a prominent, triply-imaged system at a large radius of $\sim$37" south of the BCG. We use the latest available Hubble imaging to construct an accurate lensing model for this cluster, identifying six new multiply-imaged systems with the guidance of our LTM method, so that we have roughly quadrupled the number of lensing constraints. We determine that MACS2135 is amongst the top lensing clusters known, comparable in size to the Hubble Frontier Fields. For a source at $z_{s}=2.32$, we find an effective Einstein radius of $\theta_{e}=27\pm3$", enclosing $1.12 \pm0.16 \times10^{14}$ $M_{\odot}$. We make our lens model, including mass and magnification maps, publicly available, in anticipation of searches for high-$z$ galaxies with the James Webb Space Telescope for which this cluster is a compelling target.Comment: 7 pages, 2 figures (3 subfigures in total), 1 table; Published in ApJ; V2: accepted versio

Strong Lensing Analysis of the Galaxy Cluster MACS J1319.9+7003 and the Discovery of a Shell Galaxy

We present the first strong-lensing analysis of the massive galaxy cluster MACS J1319.9+7003 (z = 0:33, also known as Abell 1722), as part of our ongoing effort to analyze massive clusters with archival Hubble Space Telescope imaging. We identified and spectroscopically measured with Keck/MOSFIRE two galaxies multiply-imaged by the cluster. Our lensing analysis reveals a modest lens, with an effective Einstein radius of θe(z = 2) = 12"1, enclosing 2.1±0.3 x 10^(13) M_☉. We brie y discuss the strong-lensing properties of the cluster, using two different modeling techniques, and make the mass models publicly-availablea. Independently, we identifieed a noteworthy, young Shell Galaxy system forming around two likely interacting cluster members, 2000 north of the Brightest Cluster Galaxy (BCG), with the smaller companion only 0.66" (~3 kpc in projection) from the host galaxy's core. Shell galaxies are rare in galaxy clusters, and indeed, a simple estimate yields that they are only expected in roughly one in several dozen, to several hundred, massive galaxy clusters (the estimate can easily change by an order-of-magnitude within a reasonable range of characteristic values relevant for the calculation). While we assume the shell galaxy is in the cluster as is also evident from its colors, we also acknowledge that spectroscopic redshifts might be needed to further secure the nature of the system. Taking advantage of our lens model best-fit, mass-to-light scaling relation for cluster members, we infer that the total mass of the shell galaxy system is 1.3 x 10^(11) M_☉, with a host-to-companion mass ratio of about 10:1. Despite being rare in high density environments, the shell galaxy constitutes an example to how stars of cluster galaxies are being efficiently redistributed to the Intra Cluster Medium. Dedicated numerical simulations for the observed shell configuration, perhaps aided by the mass model, might cast interesting insight on the interaction history and properties of the two galaxies. An archival HST search in galaxy cluster images might reveal more such systems, whose rate would be interesting to compare to our estimate

Frontier Fields: High-Redshift Predictions and Early Results

The Frontier Fields program is obtaining deep Hubble and Spitzer Space Telescope images of new "blank" fields and nearby fields gravitationally lensed by massive galaxy clusters. The Hubble images of the lensed fields are revealing nJy sources (AB mag > 31), the faintest galaxies yet observed. In this paper, we present high-redshift (z > 6) number count predictions for the full program and candidates in three of the first Hubble Frontier Fields images. The full program will transform our understanding of galaxy evolution in the first 600 million years (z > 9). Where previous programs yielded perhaps a dozen z > 9 candidates, the Frontier Fields may yield ~70 (~6 per field). We base this estimate on an extrapolation of luminosity functions observed between 4 < z < 8 and gravitational lensing models submitted by the community. However, in the first two deep infrared Hubble images obtained to date, we find z ~ 8 candidates but no strong candidates at z > 9. This might suggest a deficit of faint z > 9 galaxies as also reported in the Ultra Deep Field (even while excesses of brighter z > 9 galaxies were reported in shallower fields). At these redshifts, cosmic variance (field-to-field variation) is expected to be significant (greater than +/-50%) and include clustering of early galaxies formed in overdensities. The full Frontier Fields program will significantly mitigate this uncertainty by observing six independent sightlines each with a lensing cluster and nearby blank field.Comment: Submitted for publication in the Astrophysical Journal. 15 pages, 17 figure

"Refsdal" meets Popper: comparing predictions of the re-appearance of the multiply imaged supernova behind MACSJ1149.5+2223

Supernova "Refsdal," multiply imaged by cluster MACS1149.5+2223, represents a rare opportunity to make a true blind test of model predictions in extragalactic astronomy, on a timescale that is short compared to a human lifetime. In order to take advantage of this event, we produced seven gravitational lens models with five independent methods, based on Hubble Space Telescope (HST) Hubble Frontier Field images, along with extensive spectroscopic follow-up observations by HST, the Very Large and the Keck Telescopes. We compare the model predictions and show that they agree reasonably well with the measured time delays and magnification ratios between the known images, even though these quantities were not used as input. This agreement is encouraging, considering that the models only provide statistical uncertainties, and do not include additional sources of uncertainties such as structure along the line of sight, cosmology, and the mass sheet degeneracy. We then present the model predictions for the other appearances of supernova "Refsdal." A future image will reach its peak in the first half of 2016, while another image appeared between 1994 and 2004. The past image would have been too faint to be detected in existing archival images. The future image should be approximately one-third as bright as the brightest known image (i.e., H_(AB) ≈ 25.7 mag at peak and H_(AB) ≈ 26.7 mag six months before peak), and thus detectable in single-orbit HST images. We will find out soon whether our predictions are correct

CLASH: z ∼ 6 young galaxy candidate quintuply lensed by the frontier field cluster RXC J2248.7−4431

We present a quintuply lensed z ∼ 6 candidate discovered in the field of the galaxy cluster RXC J2248.7−4431 (z ∼ 0.348) targeted within the Cluster Lensing and Supernova survey with Hubble (CLASH) and selected in the deep Hubble Space Telescope (HST) frontier fields survey. Thanks to the CLASH 16-band HST imaging, we identify the quintuply lensed z ∼ 6 candidate as an optical dropout in the inner region of the cluster, the brightest image having mag_(AB) = 24.8 ± 0.1 in the f105w filter. We perform a detailed photometric analysis to verify its high-z and lensed nature. We get as photometric redshift z_(ph) ∼ 5.9, and given the extended nature and NIR colours of the lensed images, we rule out low-z early-type and galactic star contaminants. We perform a strong lensing analysis of the cluster, using 13 families of multiple lensed images identified in the HST images. Our final best model predicts the high-z quintuply lensed system with a position accuracy of 0.8 arcsec. The magnifications of the five images are between 2.2 and 8.3, which leads to a delensed UV luminosity of L_(1600)∼0.5L^∗_(1600) at z = 6. We also estimate the UV slope from the observed NIR colours, finding a steep β = −2.89 ± 0.38. We use singular and composite stellar population SEDs to fit the photometry of the high-z candidate, and we conclude that it is a young (age <300 Myr) galaxy with mass of M ∼ 10^8 M_⊙, subsolar metallicity (Z < 0.2 Z_⊙) and low dust content (A_V ∼ 0.2–0.4)

Triaxial strong-lensing analysis of the z > 0.5 MACS clusters: the mass-concentration relation

The high concentrations derived for several strong-lensing clusters present a major inconsistency between theoretical LambdaCDM expectations and measurements. Triaxiality and orientation biases might be at the origin of this disagreement, as clusters elongated along the line-of-sight would have a relatively higher projected mass density, boosting the resulting lensing properties. Analyses of statistical samples can probe further these effects and crucially reduce biases. In this work we perform a fully triaxial strong-lensing analysis of the 12 MACS clusters at z > 0.5, a complete X-ray selected sample, and fully account for the impact of the intrinsic 3D shapes on their strong lensing properties. We first construct strong-lensing mass models for each cluster based on multiple-images, and fit projected ellipsoidal Navarro-Frenk-White halos with arbitrary orientations to each mass distribution. We then invert the measured surface mass densities using Bayesian statistics. Although the Einstein radii of this sample are significantly larger than predicted by LambdaCDM, here we find that the mass-concentration relation is in full agreement with results from N-body simulations. The z > 0.5 MACS clusters suffer from a moderate form of orientation bias as may be expected for X-ray selected samples. Being mostly unrelaxed, at a relatively high redshift, with high X-ray luminosity and noticeable substructures, these clusters may lie outside the standard concentration-Einstein radius relation. Our results remark the importance of triaxiality and properly selected samples for understanding galaxy clusters properties, and suggest that higher-z, unrelaxed low-concentration clusters form a different class of prominent strong gravitational lenses. Arc redshift confirmation and weak lensing data in the outer region are needed to further refine our analysis.Comment: 12 pages, 12 figures; in press on MNRA