Article
Large Einstein radii: a problem for ΛCDM
Institute for Cosmic Ray Research, University of Tokyo, Kashiwa 2778582, Japan
Monthly Notices of the Royal Astronomical Society (Impact Factor: 5.52). 11/2008; 390(4):1647  1654. DOI: 10.1111/j.13652966.2008.13852.x Source: arXiv

Article: CLASH: The enhanced lensing efficiency of the highly elongated merging cluster MACS J0416.12403
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ABSTRACT: We perform a stronglensing analysis of the merging galaxy cluster MACS J0416.12403 (M0416; z=0.42) in recent CLASH/HST observations. We identify 70 new multiple images and candidates of 23 background sources in the range 0.7<z_{phot}<6.14 including two probable highredshift dropouts, revealing a highly elongated lens with axis ratio ~5:1, and a major axis of ~100\arcsec (z_{s}~2). Compared to other wellstudied clusters, M0416 shows an enhanced lensing efficiency. Although the critical area is not particularly large (~0.6 \square\arcmin; z_{s}~2), the number of multiple images, per critical area, is anomalously high. We calculate that the observed elongation boosts the number of multiple images, \emph{per critical area}, by a factor of ~2.5\times, due to the increased ratio of the caustic area relative to the critical area. Additionally, we find that the observed separation between the two main mass components enlarges the critical area by a factor of ~2. These geometrical effects can account for the high number (density) of multiple images observed. We find in numerical simulations, that only ~4% of the clusters (with M_{vir}>6 x 10^{14} h^{1}M_{\odot}) exhibit as elongated critical curves as M0416.The Astrophysical Journal Letters 11/2012; 762(2). · 6.35 Impact Factor  [Show abstract] [Hide abstract]
ABSTRACT: Lens magnification by galaxy clusters induces characteristic spatial variations in the number counts of background sources, amplifying their observed fluxes and expanding the area of sky, the net effect of which, known as magnification bias, depends on the intrinsic faintend slope of the source luminosity function. The bias is strongly negative for red galaxies, dominated by the geometric area distortion, whereas it is mildly positive for blue galaxies, enhancing the blue counts toward the cluster center. We generalize the Bayesian approach of Umetsu et al. for reconstructing projected cluster mass profiles, by incorporating multiple populations of background sources for magnification bias measurements and combining them with complementary lens distortion measurements, effectively breaking the masssheet degeneracy and improving the statistical precision of cluster mass measurements. The approach can be further extended to include stronglensing projected mass estimates, thus allowing for nonparametric absolute mass determinations in both the weak and strong regimes. We apply this method to our recent CLASH lensing measurements of MACS J1206.20847, and demonstrate how combining multiprobe lensing constraints can improve the reconstruction of cluster mass profiles. This method will also be useful for a stacked lensing analysis, combining all lensingrelated effects in the cluster regime, for a definitive determination of the averaged mass profile.The Astrophysical Journal 02/2013; 769(1). · 6.73 Impact Factor 
Article: Testing phenomenological and theoretical models of dark matter density profiles with galaxy clusters
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ABSTRACT: We use the stacked gravitational lensing mass profile of four highmass (M >~10^{15}Msun) galaxy clusters around z ~ 0.3 from Umetsu et al. to fit density profiles of phenomenological [NavarroFrenkWhite (NFW), Einasto, S\'ersic, Stadel, BaltzMarshallOguri (BMO) and Hernquist] and theoretical (nonsingular Isothermal Sphere, DARKexp and Kang & He) models of the dark matter distribution. We account for largescale structure effects, including a 2halo term in the analysis. We find that the BMO model provides the best fit to the data as measured by the reduced chi^2. It is followed by the Stadel profile, the generalized NFW profile with a free inner slope and by the Einasto profile. The NFW model provides the best fit if we neglect the 2halo term, in agreement with results from Umetsu et al. Among the theoretical profiles, the DARKexp model with a single form parameter has the best performance, very close to that of the BMO profile. This may indicate a connection between this theoretical model and the phenomenology of dark matter halos, shedding light on the dynamical basis of empirical profiles which emerge from numerical simulations.Monthly Notices of the Royal Astronomical Society 01/2013; · 5.52 Impact Factor
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