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TOPIC: Largest known lensed images
Blobrana


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MACS galaxy clusters
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Title: Discovery of radio halos and double-relics in distant MACS galaxy clusters: clues to the efficiency of particle acceleration
Authors: A. Bonafede, M Brueggen, R. van Weeren, F. Vazza, G. Giovannini, H. Ebeling, A. C. Edge, M. Hoeft, U. Klein

We have performed 323 MHz observations with the Giant Metrewave Radio Telescope of the most promising candidates selected from the MACS catalogue. The aim of the work is to extend our knowledge of the radio halo and relic populations to z>0.3, the epoch in which massive clusters formed. In MACSJ1149.5+2223 and MACSJ1752.1+4440, we discovered two double-relic systems with a radio halo, and in MACSJ0553.4-3342 we found a radio halo. Archival Very Large Array observations and Westerbork Synthesis Radio Telescope observations have been used to study the polarisation and spectral index properties. The radio halo in MACSJ1149.5+2223 has the steepest spectrum ever found so far in these objects (alpha > 2). The double relics in MACSJ1149.5+2223 are peculiar in their position that is misaligned with the main merger axis. The relics are polarised up to 30% and 40% in MACSJ1149.5+2223 and MACSJ1752.040+44, respectively. In both cases, the magnetic field is roughly aligned with the relics' main axes. The spectra in the relics in MACSJ1752.040+44 steepen towards the cluster centre, in agreement with model expectations. X-ray data on MACSJ0553.4-3342 suggests that this cluster is undergoing a major merger, with the merger axis close to the plane of the sky. The cores of the disrupted clusters have just passed each other, but no radio relic is detected in this system. If turbulence is responsible for the radio emission, we argue that it must develop before the core passage. A comparison of double relic plus halo system with cosmological simulations allows a simultaneous estimate of the acceleration efficiencies at shocks (to produce relics) and of turbulence (to produce the halo).

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Blobrana


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RE: Largest known lensed images
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Title: Metallicity Gradient of a Lensed Face-on Spiral Galaxy at Redshift 1.49
Authors: T.-T. Yuan (1), L. J. Kewley (1), A. M. Swinbank (2), J. Richard (2,3), R. C. Livermore (2) ((1) IfA, Hawaii (2) Durham, UK (3) Dark Cosmology Centre, Niels Bohr Institute)
(Version v2)

 We present the first metallicity gradient measurement for a grand-design face-on spiral galaxy at z~1.5. This galaxy has been magnified by a factor of 22 x by a massive, X-ray luminous galaxy cluster MACS J1149.5+2223 at z=0.544. Using the Laser Guide Star Adaptive Optics aided integral field spectrograph OSIRIS on KECK II, we target the Halpha emission and achieve a spatial resolution of 0.1", corresponding to a source plane resolution of 170 pc. The galaxy has well-developed spiral arms and the nebular emission line dynamics clearly indicate a rotationally supported disk with V rot/sigma ~ 4. The best-fit disk velocity field model yields a maximum rotation of V_{rot} sin{i}=150±15 km s-1, and a dynamical mass of M_{dyn}=1.3±0.2 x 1010cosec2(i) solar masses (within 2.5 kpc), where the inclination angle i=45±10°. Based on the [NII] and Halpha ratios, we measured the radial chemical abundance gradient from the inner hundreds of parsecs out to ~5 kpc. The slope of the gradient is -0.16±0.02 dex kpc-1, significantly steeper than the gradient of late-type or early-type galaxies in the local universe. If representative of disk galaxies at z~1.5, our results support an "inside-out" disk formation scenario in which early infall/collapse in the galaxy center builds a chemically enriched nucleus, followed by slow enrichment of the disk over the next 9 Gyr.

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Blobrana


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Title: Discovery of the largest known lensed images formed by a critically convergent lensing cluster
Authors: Adi Zitrin, Tom Broadhurst

We identify the largest known lensed images of a single spiral galaxy, lying close to the centre of the distant cluster MACS J1149.5+2223 (z=0.544). These images cover a total area of \simeq 150 \Box\arcsec  and are magnified \simeq 200 times. Unusually, there is very little image distortion implying the central mass distribution is almost uniform over a wide area (r\simeq200kpc) with a surface density equal to the critical density for lensing, corresponding to maximal lens magnification. Many fainter multiply-lensed galaxies are also uncovered by our model, outlining a very large tangential critical curve, of radius r\simeq 170kpc, posing a challenge for the standard LCDM-Cosmology. Because of the uniform central mass distribution a particularly clean measurement of the mass of the brightest cluster galaxy is possible here, for which we infer stars contribute most of the mass within a limiting radius of \simeq 30kpc, with a mass-to-light ratio of M/L_{B}\simeq 4.5(M/L)_{\odot}. This cluster with its uniform and central mass distribution acts analogously to a regular magnifying glass, converging light without distorting images, resulting in the most powerful lens yet discovered for accessing the faint high-z Universe.

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