The Largest Gravitational Lens: MACS J0717.5+3745 (z=0.546)

Adi Zitrin; Tom Broadhurst; Yoel Rephaeli; Sharon Sadeh

doi:10.1088/0004-637X/707/1/L102

paper

The Largest Gravitational Lens: MACS J0717.5+3745 (z=0.546)

arXiv:0907.4232 · doi:10.1088/0004-637X/707/1/L102

Abstract

We identify 13 sets of multiply-lensed galaxies around MACS J0717.5+3745 ( $z = 0.546$ ), outlining a very large tangential critical curve of major axis $\sim2.8\arcmin$, filling the field of HST/ACS. The equivalent circular Einstein radius is $θ_{e}= 55 \pm 3\arcsec$ (at an estimated source redshift of $z_{s} \sim 2.5$ ), corresponding to $r_{e} ≃ 350 \pm 20 k p c$ at the cluster redshift, nearly three times greater than that of A1689 ( $r_{e} ≃ 140 k p c$ for $z_{s} = 2.5$ ). The mass enclosed by this critical curve is very large, $7.4 \pm 0.5 \times 1 0^{14} M_{⊙}$ and only weakly model dependent, with a relatively shallow mass profile within $r < 250 k p c$ , reflecting the unrelaxed appearance of this cluster. This shallow profile generates a much higher level of magnification than the well known relaxed lensing clusters of higher concentration, so that the area of sky exceeding a magnification of $> 10 \times$ , is $\simeq 3.5\sq\arcmin$ for sources with $z ≃ 8$ , making MACS J0717.5+3745 a compelling target for accessing faint objects at high redshift. We calculate that only one such cluster, with $θ_{e}\ge 55\arcsec$, is predicted within $\sim 1 0^{7}$ Universes with $z \geq 0.55$ , corresponding to a virial mass $\geq 3 \times 1 0^{15} M_{⊙}$ , for the standard $Λ C D M$ (WMAP5 parameters with $2 σ$ uncertainties).

5 pages, 5 figures, accepted to the ApJ Letters; title modified; minor changes

The Largest Gravitational Lens: MACS J0717.5+3745 (z=0.546)

Abstract

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