Adi Zitrin, Felipe Menanteau, John P. Hughes, Dan Coe, L. Felipe Barrientos, Leopoldo Infante, Rachel Mandelbaum
We present the first strong-lensing (SL) analysis of the galaxy cluster ACT-CL J0102-4915 (El Gordo), in recent HST/ACS images, revealing a prominent strong lens at a redshift of $z=0.87$. This finding adds to the already-established unique properties of El Gordo: it is the most massive, hot, X-ray luminous, and bright Sunyaev-Zeldovich effect cluster at $z\gtrsim0.6$, and the only `bullet'-like merging cluster known at these redshifts. The lens consists of two merging massive clumps, where for a source redshift of $z_{s}\sim2$ each clump exhibits only a small, separate critical area, with a total area of $0.69\pm0.11\sq\arcmin$ over the two clumps. For a higher source redshift, $z_{s}\sim4$, the critical curves of the two clumps merge together into one bigger and very elongated lens (axis ratio $\simeq5.5$), enclosing an effective area of $1.44\pm0.22\sq\arcmin$. The critical curves continue expanding with increasing redshift so that for high-redshift sources ($z_{s}\gtrsim9$) they enclose an area of $\sim1.91\pm0.30\sq\arcmin$ (effective $\theta_{e}\simeq46.8\pm3.7\arcsec$) and a mass of $6.25\pm1.06\times10^{14}M_{\odot}$. According to our model, the area of high magnification ($\mu>10$) for such high redshift sources is $\simeq0.95\sq\arcmin$, and the area with $\mu>5$ is $\simeq1.92\sq\arcmin$, making El Gordo a compelling target for studying the high-redshift Universe. We obtain a strong lower limit on the total mass of El Gordo, $\gtrsim1.7\times10^{15}M_{\odot}$ from the SL regime alone, suggesting a total mass of, roughly, $M_{200}\sim2.3\times10^{15}M_{\odot}$. The presented mass model could be improved with future HST imaging.
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http://arxiv.org/abs/1304.0455
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