CLASH: New Multiple Images Constraining the Inner Mass Profile of MACS J1206.2-0847

Abstract. We present a strong-lensing analysis of the galaxy cluster MACS J1206.2-0847 (z = 0.44) using UV, Optical, and IR, HST/ACS/WFC3 data taken as part of the CLASH multi-cycle treasury program, with VLT/VIMOS spectroscopy for some of the multiply lensed arcs. The CLASH observations, combined with our mass model, allow us to identify 47 new multiply lensed images of 12 distant sources. These images, along with the previously known arc, span the redshift range 1 <~ z <~ 5.5, and thus enable us to derive a detailed mass distribution and to accurately constrain, for the first time, the inner mass profile of this cluster. We find an inner profile slope of dlog Σ/dlog θ ~= -0.55 ± 0.1 (in the range [1'', 53''], or 5 kpc <~ r <~ 300 kpc), as commonly found for relaxed and well-concentrated clusters. Using the many systems uncovered here we derive credible critical curves and Einstein radii for different source redshifts. For a source at zs ~= 2.5, the critical curve encloses a large area with an effective Einstein radius of θ E = 28'' ± 3'', and a projected mass of (1.34 ± 0.15) × 1014 M sun. From the current understanding of structure formation in concordance cosmology, these values are relatively high for clusters at z ~ 0.5, so that detailed studies of the inner mass distribution of clusters such as MACS J1206.2-0847 can provide stringent tests of the ΛCDM paradigm.

Galaxy cluster MACS1206 (z = 0.4385) imaged with HST/ACS/WFC3. North is up and east is left. We number the multiply lensed images used and uncovered in this work. The numbers indicate the 50 lensed images, 47 of which are uncovered here and correspond to (at least) 12 newly identified sources and candidates, and the different colors are used to distinguish between them. Note that candidate systems are marked in “c.” Details on the each system are given in Table 1. The overlaid white critical curve corresponds to system 4 at zs = 2.54, enclosing a critical area with an effective Einstein radius of ≃160 kpc at the redshift of this cluster (28′′). The blue critical curve corresponds to the lower redshift of system 1, the giant arc system at zs = 1.033. The composition of this color image is red = F105W+F110W+F125W+F140W+F160W, green = F606W+F625W+F775W+F814W+F850LP, and blue = F435W+F475W. The bottom left inset shows an enlargement of the central core.