Day 677

Thursday.

1406.2702
A rigorous free-form lens model of Abell 2744 to meet the Hubble frontier fields challenge
Lam, Broadhurst, Diego, Lim, Coe, Ford, Zheng

Deep Hubble Frontier Fields (HFF) imaging of the most powerful lensing clusters provides access to the most magnified distant galaxies.  It is a challenge to construct lens models capable of describing these complex massive, merging clusters so that the intrinsic source properties can be meaningfully derived.  Apply the general free-form lensing method (WSLAP+) to A2744, providing a model independent map of the cluster magnification and geometric distance estimates to multiply-lensed sources.  Solve simultaneously for a smooth cluster component on a pixel grid, together with local deflections by the observed member galaxies.  Solution is sufficiently accurate to securely identify 18 multiply-lensed systems behind A2744 totally 56 images, spanning 1.0<z<7.5.  Model corrects and completes several systems recently claimed using the same data.  The reconstructed mass shows a small enhancement in the direction where significant amount of hot plasma can be seen in X-rays.  Compare photometric redshift estimates with "geometric redshifts", derived from the relative angles between the multiple images, finding tight agreement and consistency with the standard cosmological parameters.  Predicted and observed magnitudes were found to agree with each other in general, but further refinement in the lens model is required such that the magnification can be accurately corrected.  Intriguingly, no multiply-lensed galaxy is detected beyond z=7.5, despite the high magnification and the limiting redshift of z=11.5 permitted by the HFF filters.  With the additional HFF clusters, can better examine the plausibility of any pronounced high-z deficit, averaging over clustering noise, with potentially important implications for the epoch of deionization and the nature of dark matter.

1406.2872
3C 220.3: a radio galaxy lensing a submillimeter galaxy
Haas, ... et al

Herschel Space Observatory photometry and extensive multi wavelength followup have revealed that the powerful radio galaxy 3C 220.3 at z=0.685 acts as a gravitational lens for a background SMG at z=2.221.  At an observed wavelength of 1mm, the SMG is lensed into 3 distinct images.  In the observed near infrared, these images are connected by an arc of 1.8" radius forming an Einstein half-ring centered near the radio galaxy.  In the visible light, only the arc is apparent.  3C 220.3 is the only known instance of strong galaxy-scale lensing by a powerful radio galaxy not located in a galaxy cluster and therefore it offers the potential to probe the DM content of the rail galaxy host.  Lens modeling rejects a single lens, but two lenses centered on the radio galaxy host A and a companion B, separated by 1.5", provide a fit consistent with all data and reveal faint candidates for the predicted fourth and fifth images.  The model does not require an extended common dark halo, consistent with the absence of extended bright X-ray emission on the Chandra image.  The projected DM fractions within the Einstein radii of A(1.02") and B(0.61") are about 0.4pm0.3 and 0.55pm0.3.  The mass to i-band light ratios of A and B, M/L~8pm4 Msun/Lsun, appear comparable to those of radio-quiet lensing galaxies at the same redshift in the CASTLES, LSD, and SL2S samples.  The lensed SMG is extremely bright with observed f(250um)=440mJy owing to a magnification factor mu~10.  The SMG spectrum shows luminous, narrow CIV 154.9nm emission, revealing that the SMG houses a hidden quasar in addition to a violent starburst.  Multicolor image reconstruction of the SMG indicates a bipolar morphology of the emitted UV light suggestive of cones through which UV light escapes a dust-enshrouded nucleus.

1406.2967
Characterizing simulated galaxy stellar mass histories
Cohn, van de Voort

Galaxy formation simulations can now predict many galaxy properties and their evolution through time.  Classify ensembles of simulated stellar mass histories, holding fixed their z=0 stellar mass.  Applied PCA to stellar mass histories from the DM + SAM Millennium sim and the hydrodynamical OverWhelmingly Large Simulations (OWLS) project, finding that a large fraction of the total scatter around the average stellar mass history for each sample is due to only one PCA fluctuation.  This fluctuation differs between some different models sharing the same z=0 stellar mass and between lower (<=3e10 Msun) and higher final stellar mass Millennium samples.  Correlated the PCA characterization with several z=0 galaxy observables (in principle observable in a survey) and galaxy halo history properties.  Also explored separating galaxy stellar mass histories into classes, using the largest PCA contribution, k-means clustering, and simple Gaussian mixture models.  For three component models, these different methods often had significant overlap.  Provide several classification quantities for the Millennium and OWLS stellar mass histories, which can be compared with other simulation histories as well.  These history classification methods provide a succinct and often quick way to characterize changes in histories of a simulated population as physical assumptions are varied, to compare histories of different simulated populations to each other, and to assess the relation of simulated histories to fixed time observations.